OUTLINES   OF   INDUSTKIAL   CHEMISTEY 


THE  MACMILLAN  COMPANY 

NEW  YORK   •    BOSTON   •    CHICAGO   •    DALLAS 
ATLANTA   •    SAN   FRANCISCO 

MACMILLAN  &  CO.,  LIMITED 

LONDON    •    BOMBAY   •    CALCUTTA 
MELBOURNE 

THE  MACMILLAN  CO.  OF  CANADA,  L 

TORONTO 


OUTLINES 


OF 


INDUSTRIAL  CHEMISTRY 

A  TEXT-BOOK  FOR  STUDENTS 

BY 

FRANK   HALL   THORP,   PH.D. 


WITH    ASSISTANCE   IN    REVISION    FROM 

WARREN   K.    LEWIS,   PH.D. 

PROFESSOR   OF   CHEMICAL   ENGINEERING    IN    THE   MASSACHUSETTS 
INSTITUTE   OF   TECHNOLOGY 


THIRD  REVISED  AND  ENLARGED  EDITION 


THE   MACMILLAN   COMPANY 

LONDON:  MACMILLAN  &  CO.,  LTD. 
1916 

All  rights  reserved 


COPYRIGHT,  1898,  1905,  AND  1916, 
BY  THE  MACMILLAN  COMPANY. 


Set  up  and  electrotyped.  Published  November,  1898.  Reprinted, 
with  corrections,  November,  1899. 

New  edition,  corrected  and  enlarged,  May,  1905;  April,  1907; 
January,  October,  1908;  August,  1909;  April,  1911;  September, 
1912;  August,  1913;  September,  1914. 

Third  edition,  revised,  May,  1916.  Reprinted  November,  1916. 


Norfaootr 

J.  8.  Gushing  Co.  —  Berwick  &  Smith  Co. 
Norwood,  Mass.,  U.S.A. 


3E0  tfje  fHemxjrjj  ot 
LEWIS   MILLS   NORTON 

DURING    NINE    YEARS    PROFESSOR    OF    INDUSTRIAL   CHEMISTRY 
IN    THE   MASSACHUSETTS    INSTITUTE    OF    TECHNOLOGY 

<Tf)ts  Book  is  DrttratetJ 

IN   TOKEN   OF   WARM   PERSONAL   REGARD   FOR   THE   KINDLY   MAN 

AND   GRATEFUL   APPRECIATION   OF 
THE   HELPFULNESS   AND   INSPIRATION   OF   HIS   TEACHING 

THE  AUTHOR 


346430 


PREFACE   TO   THE  FIRST  EDITION 

THE  object  of  this  book  is  to  furnish,  an  elementary  course  in 
Industrial  Chemistry,  which  may  serve  as  the  ground  work  for 
a  more  extended  course  of  lectures,  if  desired.  The  writer  has 
endeavored  to  describe  briefly,  within  the  limits  of  one  moderate- 
sized  volume,  the  more  important  industrial  chemical  processes,  but 
omitting  matters  of  detail  which  properly  belong  in  the  larger  hand- 
books. Numerous  references  are  made  in  the  text  to  periodicals 
and  journals,  and  to  the  standard  handbooks  and  encyclopaedias 
and  many  special  works,  where  details,  lacking  in  this  book,  may 
be  found.  The  bibliographical  lists  following  each  section  are  not 
complete,  but  only  include  those  works  which  will  usually  be  found 
in  most  chemical  libraries ;  the  references  to  the  journal  literature 
are  merely  those  articles  to  which  the  author's  attention  has  been 
drawn  in  the  preparation  of  class-room  exercises.  The  diagrams 
illustrating  the  text  have,  in  most  cases,  been  drawn  as  simply  as 
possible,  purposely  showing  only  the  essential  features. 

In  the  selection  and  order  of  arrangement  of  the  several  sub- 
jects, the  author  has  necessarily  been  influenced  by  his  work  in  this 
Institute  and  the  requirements  of  his  own  class,  but  it  is  believed 
that  the  book  as  a  whole  will  be  found  applicable  to  the  work  in 
most  institutions  of  learning  where  industrial  chemistry  is  taught. 
The  subject  of  Metallurgy  has  been  entirely  omitted,  since  there  are 
already  several  excellent  brief  text-books  dealing  with  it  alone,  and 
instruction  in  it  is  generally  given  independently  of  that  relating  to 
technical  chemistry.  Likewise  the  important  subject  of  the  coal-tar 
colors  has  been  condensed  into  the  briefest  possible  outline,  because 
this  is  nearly  always  included  in  courses  in  organic  chemistry,  and 
there  are  several  small  manuals  treating  of  it.  Analytical  processes 
have  also  been  omitted  as  foreign  to  the  intended  scope  and  purpose 
of  the  book. 

It  is  assumed  that  students  taking  this  course  are  familiar  with 
the  elements  of  general  chemistry,  both  inorganic  and  organic,  and 
with  the  elements  of  physics. 

In  the  compilation  of  this  work,  free  use  has  been  made  of  many 

vii 


viii  PREFACE 

of  the  standard  English,  German,  and  French  hand-books  and  ency- 
clopaedias, particularly  of  Professor  T.  E.  Thorpe's  Dictionary  of 
Applied  Chemistry,  the  works  of  Professor  Lunge  on  Sulphuric 
Acid  and  Alkali,  and  Coal-tar  and  Ammonia,  Ost's  Technischen 
Chemie,  and  Dainmer's  Handbuch  der  chemischen  Technologic. 

The  following  business  firms  have  courteously  loaned  cuts  and 
drawings  for  the  illustrations  :  Curtis  Davis  &  Co.,  Cambridgeport, 
Mass.,  slabbing  machine  and  soap  kettle  ;  William  Campbell  &  Sons, 
Cambridgeport,  Mass.,  rendering  tank ;  The  De  La  Vergne  Refriger- 
ating  Machine  Co.,  New  York,  refrigerating  machine  ;  H.  L.  Dixon, 
Pittsburg,  Pa.,  tank  furnace  for  glass;  United  Gas  Improvement 
Co.,  Philadelphia,  water  gas  plant ;  John  Johnson  &  Co.,  New  York, 
filter  press ;  Sernet-Solvay  Company,  Syracuse,  N.Y.,  coke  oven ; 
R.  D.  Wood  &  Co.,  Philadelphia,  Pa.,  Taylor  gas  producer. 

The  writer  wishes  to  acknowledge  his  indebtedness  to  the  fol- 
lowing friends  for  assistance  and  advice  in  the  revision  of  those 
portions  of  the  work  treating  of  their  specialties :  C.  D.  Jenkins, 
State  Gas  Inspector  of  Massachusetts,  Illuminating  Gas ;  A.  D. 
Little,  Consulting  Chemist,  Wood  Pulp  and  Paper  ;  J.  W.  Loveland, 
Superintendent  Curtis  Davis  &  Co.,  Soap  Manufacturers,  Soap, 
Candles,  and  Glycerine;  F.  G.  Stantial,  Superintendent  Cochrane 
Chemical  Co.,  Sulphuric,  Hydrochloric,  and  Nitric  Acids ;  the  fol- 
lowing members  of  the  instructing  staff  of  the  Massachusetts  Insti- 
tute of  Technology :  Professor  A.  H.  Gill,  Fuels  and  Oils ;  G.  W. 
Rolfe,  Starch,  Glucose,  and  Sugar;  S.  C.  Prescott,  Fermentation 
Industries ;  J.  W.  Smith,  Textile  Industries. 

Special  thanks  are  due  to  Dr.  W.  R.  Whitney,  of  the  Institute  of 
Technology,  for  much  assistance  in  the  proof-reading,  and  also  to 
Dr.  B.  L.  Robinson,  Curator  of  the  Gray  Herbarium,  Harvard  Uni- 
versity, for  his  painstaking  revision  of  the  botanical  nomenclature. 

In  the  labor  of  preparation  of  the  book,  the  author  has  also  had 
much  help  from  his  wife,  who  copied  the  entire  manuscript  and  has 
assisted  in  the  reading  of  all  of  the  proof. 

FRANK   H.    THORP. 
BOSTON,  MASS.,  October,  1898. 

In  this  new  edition,  such  errors  as  have  been  brought  to  the 
writer's  notice  have  been  corrected,  but  material  changes  have  not 
been  generally  attempted,  owing  to  press  of  other  work.  The  author 
wishes  to  express  his  indebtedness  to  those  who  have  called  attention 
to  weak  parts  in  the  book,  and  heartily  invites  further  criticism. 

F.  H.  T. 

BOSTON,  MASS.,  October,  1899. 


PREFACE   TO  THE   SECOND   EDITION 

THE  important  advances  made  in  the  chemical  industries  since 
the  appearance  of  the  first  edition,  and  the  establishment  of  several 
successful  manufactures  which  at  that  time  were  not  beyond  the 
experimental  stage,  have  necessitated  giving  the  text  considerable 
revision,  with  material  additions  and  corrections.  Such  errors  of 
statement  or  of  proof-reading  as  have  been  noted  have  been  cor- 
rected, and  further  criticism  by  instructors  and  others  interested 
in  the  subject  is  invited. 

It  appeared  desirable  that  a  short  outline-  of  elementary  metal- 
lurgy should  be  included,  in  order  that  the  book  might  better  meet 
the  requirements  of  the  courses  of  study  of  certain  colleges  and 
technical  schools.  With  the  exception  of  the  paragraphs  upon 
bismuth,  cadmium,  and  magnesium,  this  has  been  prepared  by  Mr. 
Chas.  D.  Demond,  and  is  now  included  as  Part  III  of  the  new 
edition. 

In  connection  with  the  material  introduced,  the  writer  wishes 
to  express  here  his  obligations  to  the  following  firms  for  permission 
to  make  abstracts  and  copy  illustrations  from  their  publications 
and  catalogues :  The  Allis-Chalmers  Co.,  Chicago ;  The  Engineering 
and  Mining  Journal,  New  York ;  The  Sugar  Apparatus  Manufactur- 
ing Co.,  Philadelphia. 

F.  H.  T. 

BOSTON,  April,  1905. 


ix 


PREFACE   TO   THE   THIRD   EDITION 

THE  great  progress  which  has  been  made  in  Chemical  Industry 
since  the  publication  of  the  second  edition  of  this  work  in  1905  has 
necessitated  entire  rewriting  of  many  sections  of  the  book,  with 
elimination  of  much  obsolete  matter  and  the  introduction  of  much 
new  material.  While  the  general  plan  of  the  former  editions  has 
been  retained,  in  treating  the  various  subjects  use  has  been  made  of 
the  modern  concepts  and  theories  of  chemistry  wherever  these 
promised  to  make  clearer  the  phenomena  involved.  Extended  math- 
ematical or  theoretical  discussion  of  the  processes  has  been  avoided 
as  beyond  the  scope  of  the  book.  It  is  not  supposed  that  the  expert 
will  find  this  book  a  guide  in  his  own  particular  field,  for  its  purpose 
is  to  impart  to  students  and  others  not  already  familiar  with  the 
processes  of  chemical  industry,  some  knowledge  of  the  plant  and 
methods  employed  in  the  more  important  manufacturing  operations 
based  upon  chemical  changes. 

F.  H.  T. 

W.  K.  L. 
BOSTON,  March,  1916. 


TABLE   OF   CONTENTS 
PART  I 


INORGANIC   INDUSTRIES 


INTRODUCTION 

Objects  of  Industrial  Chem- 
istry     

Lixiviation 

Levigation 

Evaporation 

Spontaneous  .... 
By  direct  heat  .  .  .  , 
By  steam  heat  .... 

In  vacuum 

Vacuum  pans     .     .     . 
Multiple  effect  systems 
Yaryan  evaporator  . 
Kestner  evaporator 
Lillie  evaporator 

Distillation 

Fractional  condensation 
Dephlegmation     .... 
Coupler's  still    .... 
French  column  apparatus 

Coffey  still 

Sublimation 

Filtration 

Bag  niters 

Suction  filtration  .... 
Pressure  filtration,  with  the 
filter  press     .     .     .  ':-._• 
By  use  of  leaf  filter     ... 
Centrifugal  filtration     .     . 
Sand  filters       .     ...     «, 

Crystallization 

Calcination 

•Reverberatory  furnace  .  . 
Revolving  furnace  .  .  . 
Muffle  furnace  .... 
Shaft  furnace  or  kiln  . 


1 

2 

2 

3 

3 

4 

5 

5 

5 

6 

6 

7 

8 

9 

10 

11 

12 

12 

12 

14 

14 

15 

15 

15 
17 

18 
19 
19 
20 
21 
21 
22 
22 


Refrigeration 23 

Compression  machines  .     .23 

Absorption  machines     .     .  23 

Chilling  by  compressed  air  25 

Specific  Gravity  .....  25 

Hydrometers 25 

Pyknometer 27 

Westphal's  balance   .     .     .  28 

Surface      Phenomena      and 

Colloids 28 

Disperse  systems  ....  28 

Colloids 30 

FUELS 

Solid  fuels 32 

Wood,  peat,  lignite,  brown 
coal,  bituminous  coal, 
anthracite,  charcoal, 

coke 32-37 

Beehive  coke  oven     .     .  35 

By-product  coke  ovens    .  36 

Liquid  fuels 38 

Crude    petroleum   and   oil 

residues 38 

Gaseous  fuels 38 

Natural  gas      ....'.  38 

Coal  gas 39 

Water  gas 39 

Producer  gas 41, 

Siemens'  gas  producer    .  42 

Taylor's  gas  producer      .  42 

Mond's  gas  process     .     .  43 

Blast  furnace  gas      ...  43 

WATER 

Sources  of  natural  waters       .  46 

Impurities  of  natural  waters  .  46 


XI 


Xll 


TABLE   OF   CONTENTS 


PAGE 

Hard,  soft,  saline,  alkaline  .  47 
Purification  by  chemical  pre- 
cipitation       48 

Boiler  scale 50 

Classification      of      boiler 

waters  for  locomotives     .  52 
Water  for  various  special  in- 
dustries    52 

SULPHUR 

Extraction  from  its  ores    .     .  55 

Recovered  sulphur  ....  57 

Sulphur  derivatives      .     .    58-61 

Sulphur  dioxide    ....  58 

Sodium  bisulphite     ...  59 

Calcium  bisulphite    ...  60 

Hydrosulphurous  acid  ...  60 

Sodium  hydrosulphite   .     .  60 

Sodium  thiosulphate      .     .  61 

SULPHURIC  ACID 

Commercial  grades  of  acid      .  62 
Theories  of  the  formation  of 

the  acid  in  chamber  process  63 
Materials  for  manufacture  of 

the  acid 66 

Brimstone 66 

Pyrites    . 66 

Pyrites  burners  for  lump 

ore 67 

Pyrites       burners       for 

''fines" 68 

Glover  tower 70 

Lead  chambers     ....  70 
Gay-Lussac  tower     .     .     .71 

Acid  egg      . 73 

Kestner's  elevator     .     .     .  73 

Air-lift  elevator  for  acid     .  74 

Concentration  of  acid    .     .  74 
Porcelain  and  fused  silica 

vessels 74 

Glass  and  platinum  stills  75 

Cast-iron  stills  ....  76 

Kessler's  apparatus    .     .  76 

Lunge's  plate  tower  ...  77 

Barbier's  tower  system  .     .  78 

Catalytic  processes  for  acid 

making 79 


Purification  of  gases  for 

contact  process  ...     81 
Fuming  sulphuric  acid  .     .     82 

SALT 

Sources  of  salt 83 

Preparation  of  salt  by  various 
processes 84-87 

HYDROCHLORIC   ACID    AND   SODIUM 
SULPHATE 

Salt-cake  furnaces    ....  88 

Open  roaster 88 

Muffle  roaster 89 

Coke  tower  for  acid  absorp- 
tion      90 

Bombonnes  or  tourills  for  acid 

condensation    .....  90 

Hargreaves-Robinson  process 

for  sodium  sulphate  ...  92 

Sodium  sulphate  or  salt-cake  92 

SODA  INDUSTRY 

Leblanc  process 94 

Black-ash   or   balling   fur- 
nace      95 

Lixiviation  of  black-ash      .     97 
Carbonation,    purification, 
and  evaporation  of  tank 

liquor 98 

Thelan's  pan 100 

Soda  crystals  or  sal  soda      .  100 

Caustic  soda 101 

Loewig's  process    .     .     .  102 

Tank  waste 103 

Methods  of  treating  tank 

waste    ....     104-107 
Ammonia  soda  process      .     .  107 
Carbonating  tower    .     .     .  108 
Parnell-Simpson   modifica- 
tion of  this  process     .     .111 
Frasch    process    for    caustic 

soda HI 

Cryolite  soda  process    .     .     .113 

CHLORINE  INDUSTRY 

Processes    using    manganese 

oxides 115-118 

Dunlop's  method      .     .     .117 
Weldon's  process .     .     .     .117 


TABLE   OF   CONTENTS 


Xlll 


Deacon's  process  with  copper 
salts 118 

Processes  employing  nitric 
acid 121 

Magnesia  processes  for  chlo- 
rine      122 

Weldon-Pechiney  process  .  123 

Processes  for  recovering 
chlorine  from  ammonia- 
soda  waste  liquor  .  .  .  123 

Electrolytic      Processes     for 
chlorine      and      caustic 

soda 124 

Le  Sueur's  process  .  .  .126 
Carmichael's  apparatus  .  126 
Hargreaves-Bird  apparatus  126 

Townsend  cell 127 

Griesheim-Elektron  process  127 
Castner's  process  .  .  .128 

Whiting's  cell 128 

Bell's  apparatus  ....  129 
Rhodin's  apparatus  .  .  .  129 
Gravity  cell  .  .  .  .;  .  129 
Acker  process 130 

Hypochlorites      T    .     .     .     .  131 
Bleaching      powder      and 
bleach  liquors   .     .     131-132 

Chlorates    .     .     .     .     .     ."     .'135 

Perchlorates    .     .     .,.     .     .  135 

Persulphates  .     .  „.     .     .     .136 

NITRIC  ACID 

Methods  of  manufacture   .     .  137 
Cylindrical  iron  retorts  for 

nitric  acid 138 

Guttmann's  apparatus  .     .  138 

Hart's  apparatus  ....  139 

Valentiner's  process  .     .     .140 

Rhenania  process      .     .     .140 

Fuming  nitric  acid  ....  141 

Nitric  acid  from  the  nitrogen 

of  the  air 142 

Bradley      and      Lovejoy's 

process 142 

Birkeland        and        Eyde 

process 142 

Schoenherr  process    .     .     .  143 

Pauling  process     ....  144 

Commercial  nitrates          145-149 


PAGE 

AMMONIA 

Sources  of  ammonia     .     .     .  150 

Synthetic  preparation  of  am- 
monia       150 

Frank  and  Caro  process  .  150 
Haber's  process  ....  150 
Serpek's  process  ....  151 

Ammonia  from  gas  liquor  .  .  151 
Feldmann's  apparatus  .  .152 
Griineberg-Blum  apparatus  152 

Ammonia  from  distillation  of 
waste  animal  matter      .     .153 

Distillation  of  peat  as  source 
of  ammonia      .     .     .     .     .  153 

Ammonium    salts    of    com- 
merce           154-155 

POTASH  INDUSTRY 

Sources  of  potassium  salts  .  156 
Potash  from  wood  ashes  .  156 
Potash  from  beet  sugar 

molasses 157 

Potash  from  wool  scourings  157 
Potash  from  sea- weeds  .     .158 
Stassfurt  deposit  of  potas- 
sium salts 158 

Potassium  salts  of  commerce  162 

FERTILIZERS 

Requisites  of  a  fertilizer     .     .  164 

Waste  materials  as  sources  of 

fertilizer  products .     .     .  165 
Blood,      bones,      garbage, 
"tankage,"  etc.      .     165-166 

Peruvian      and      fossil      gua- 
nos          166-167 

Phosphate  rocks 167 

Apatite 167 

Phosphorites    .'  *  •'*.     .     .  168 

Superphosphates  .,  ".  »  .  169 
Reverted  phosphate .  .  .170 

Phosphatic  slag   .     .     .     ,     .171 

Gypsum     or     "plaster"     as 
fertilizer 173 

Sewage  as  fertilizer       .     .     .173 

LIME,    CEMENT,    AND    PLASTER   OP 
PARIS 

Lime 175 

Properties  of  Lime    .     .     .175 


XIV 


TABLE  OF  CONTENTS 


PAGE 

Lime  burning 175 

Limekilns    .     .     .     175-177 
Hydraulic  lime     .     .     .     .178 

Mortar 179 

Sand-lime  bricks  ....  180 

Cements 181 

Manufacture  of  cement  182-189 
Kilns    for     burning     ce- 
ment    ....     185-187 
Mills  for  cement  grind- 
ing       187-189 

Constitution    of    Portland 

cement 190 

Hardening  of  cement     .     .190 

Testing  of  cement     .     .     .191 

Plaster  of  Paris 193 

GLASS 

Properties    and    composition 

of  glass 196 

Lime  and  lead  glass  .  .  .197 
Materials  for  glass  making  197 
Glass  furnaces  .  .  199-201 
Glass  pots,  open  and  closed  201 
General  process  of  glass 
making  ....  202-203 

Plate  glass 204 

Window  glass  and  glass  blow- 
ing       205 

Crown  glass 206 

Cut  glass  and  pressed  ware   .  206 

Tempered  glass 207 

Compound  glass  .....  207 
Colored  glass  ....     207-209 

Enamel . 209 

Iridescent  glass 209 

Mirrors 209 

CERAMIC  INDUSTRIES 

Kaolin  or  china  clay     .     .     .212 
Fire-clay,  pipe-  or  ball-clays  213 
Empirical    and   rational   an- 
alyses of  clays     .     .     .     .214 

Ceramics 215 

Non-porous  ware       .     .     .215 

Porcelains 215 

Stoneware 216 

Kilns  .  .     .  217 


PAGE 

Porous  ware 217 

Faience     and     common 

pottery 217 

Tiles .  218 

Vitrified,        encaustic, 

and  glazed  tiles    .     .  218 
Glazes 219 

Crazing  of  glaze      .     .219 

Terra  cotta 220 

Bricks 220 

Fire-brick      ....  221 

PIGMENTS 

White  pigments  .     .     .     223-231 

White  lead 223 

Dutch  process  ....  223 

Chamber  process  .     .     .  225 

Carter's  process     .     .     .  226 

Thenard's  process       .     .  226 

Electrolytic  processes      .  227 

Liickow  process      .     .  228 

Substitutes  for  white  lead  229 

Sublimed  white  lead    .  229 

Lead  sulphite     .     .     .  229 

Pattinson's  white  lead    229 

White     zinc     or     Chinese 

white  .     .    ' 229 

.Lithopone 230 

'Barytes 230 

Gypsum,  terra  alba  .     .     .231 
Whiting  or  Paris  white  .     .231 

China  clay 231 

Blue  pigments     .     .     .     231-235 

Ultramarine 231 

Prussian  or  Berlin  blue      .  233 

Smalt 234 

Cobalt  blue 235 

Copper  blues 235 

Indigo 235 

Green  pigments  .  .  .  236-238 
Ultramarine  green  .  .  .  236 
Brunswick  green  ....  236 
Chrome  greens  ....  236 
Guignet's  green  .  .  .  .237 
Copper  greens,  malachite 

and  verdigris     ....  237 
Copper-arsenic  greens    .     .  238 
Scheele's       and       Paris 
greens  .     .     .     .     .     .  238 


TABLE   OF  CONTENTS 


XV 


PAGE 

Terra  verde 238 

Yellow  pigments  .  .  238-241 
Chrome  yellows  ....  238 
Yellow  ochre  and  siennas  .  240 
Cadmium  yellow  ....  240 
Orpiment  or  royal  yellow  .  240 

Litharge 241 

Gamboge 241 

Indian  yellow  or  purree  .     .241 

Orange  pigments  ....  241 
Orange  mineral  .  .  .  .241 
Antimony  orange  .  .  .  242 

Red  pigments      .     .     .     242-246 

Red  lead 242 

Chrome  red   or  American 

vermilion 243 

Red  ochre,  Indian  red,  light 

red 243 

Iron    reds,    Venetian    red,, 
rouge,  colcothar     .     .     .  243 

Vermilion 244 

Realgar  and  antimony  reds  245 
Carmine  and  "  lakes  "     .     .  245 

Brown  pigments 246 

Umbers,  Vandyke  brown   .  246 
Sepia 247 

Black  pigments   .     .     .     247-248 

BROMINE 

Sources,  and  methods  of  ex- 
traction from  them  .     .     .  249 
Bromides 251 

IODINE 

Extraction  from  kelp  and 
varec 252 

Recovery  from  mother- 
liquors  of  sodium  nitrate 
industry .  253 

Iodides  .     .     .     .  '  .     .     .     .254 

PHOSPHORUS 

Preparation  from  bone-ash     .  256 
Preparation     from     mineral 

phosphates 256 

Readman's  electric  furnace 

process  for  reduction  .     .  257 
Matches  .  258 


BORIC  ACID 

Sources  and  preparation   .     .  260 

Borax 261 

Perborates 263 

ELECTRIC  FURNACE  PRODUCTS 

Carborundum 264 

Artificial  graphite     .     .     .     .265 

Calcium  carbide 266 

Calcium  cyanamide      .     .     .  267 

Alundum .  267 

Barium  hydroxide    ....  268 
Cyanides 268 

ARSENIC  COMPOUNDS 

Arsenious  acid,  white  arsenic  269 

Arsenic  acid 269 

Arsenates,  sodium  and  lead  270 
Arsenites,  sodium      .     .     .  270 

WATER-GLASS  .  271 


PEROXIDES 

Barium  peroxide 
Hydrogen  peroxide 
Sodium  peroxide 


272 
272 
273 


OXYGEN 

Preparation  from  potassium 

chlorate 275 

Boussingault-Brin  process  of 

preparation 275 

Deville's  process .  .  .  .  .  276 
Tessie  du  Motay  process  .  .  276 
Linde  refrigeration  process  .  277 
By  electrolysis  of  water  .  .  277 

SULPHATES 

Ferrous   sulphate,  green  vit- 
riol, copperas 279 

Copper  sulphate,  blue  vitriol, 

bluestone 280 

Zinc  sulphate,  white  vitriol  .  281 
Aluminum  sulphate,  from 

clay  and  from  bauxite      .  282 
Bayer's    process   for    pure 

alumina 283 

Aluminum      sulphate      from 

cryolite 284 

Alum 285 

Preparation  fromalunite    .  286 


XVI 


TABLE   OF   CONTENTS 


Preparation     from     alum 

shales  or  slate   ....  286 
"Neutral  alum"  ....  287 

Sodium  alum 287 

Iron    alums    and    chrome 
alum 288 

CYANIDES 

Preparation  from  ammonia 
and  carbon  at  high  tem- 
peratures   289 

Recovery    of    cyanide    from 

coal  gas  by  Bueb's  process  289 
Bunsen-Playfair    process    of 

preparation 290 

Raschen's  process     ....  290 
Ammonium       sulphocyanide 
from    carbon    disulphide 
and  ammonia  by  Gelis 
process 290 


PAGE 

Recovery  from  spent  iron 

oxide  of  gas  purifiers  .     .291 
Potassium    ferrocyanide,    re- 
covery from  spent  iron 

oxide 291 

Preparation     from     waste 

nitrogenous  matter     .     .  292 
Potassium    ferricyanide,    red 

prussiate  of  potash    .     .     .  293 

Potassium  cyanide  ....  294 

Beilby's  process    ....  295 

Castner's  process       .     .     .  295 

CARBON  BISULPHIDE  .  .  297 


CARBON  TETRACHLORIDE 


.  298 


MANGANATES  AND  PERMANGA- 
NATES    ...  .  299 


PART  II 


ORGANIC  INDUSTRIES 


DESTRUCTIVE      DISTILLATION      OF 

WOOD 

Pyroligneous  acid     .     .     .     .301 
Kilns  and  retorts  for   wood 

distillation 302 

Methyl  alcohol  or  wood  spirit  305 

Acetone 305 

Acetic  acid 306 

Acetates 308 

Wood-tar 309 

Creosote  oil 310 

Stockholm  tar       ....  310 

DESTRUCTIVE      DISTILLATION      OF 
BONES 

Bone  oil 311 

Bone-black 311 

ILLUMINATING  GAS 

Carburetted  water-gas      .     .  312 

Coal-gas 314 

Plant  for  distilling  coal  for 
gas 315 


Purification  of  gas     .     .     .  320 
Feld  process  of  purifica- 
tion       321 

Recovery      of      cyanide 
from  coal-gas     .     .     .  322 

Oil  gas 323 

Blau  gas 324 

Acetylene 324 

Air  gas 325 

COAL-TAR 

Properties  of  tar 327 

Distillation  of  tar     .     .     .     .  327 

First  runnings 330 

Light  oil 330 

Naphtha 330 

Carbolic  oil 331 

Creosote  oil      .....  332 

Naphthalene 332 

Anthracene  oil      ....  332 

Pitch 333 

Yields  of  crude  and  pure 

products  from  tar  .     .     .  333 


TABLE   OF  CONTENTS 


XVll 


MINERAL  OILS 

Petroleum  industry       .     .     .  334 
Distribution  and  origin  of 

petroleum 334 

Oil-well  drilling     .     .     .     .336 

Crude  petroleum  ....  338 

Refining  of  petroleum    .     .  339 

' '  Cracking ' '  of  heavy  oils    .  340 

Purification  of  distillates     .  341 

Burning  oils      ....  342 

Paraffine  oils     ....  342 

"Neutral  oils"       ...  342 

Spindle   oils,    machinery 

oils,  cylinder  oils      .     .  343 
Reduced  oils     .     .     .     .343 

Vaseline 343 

Russian  petroleums  .     .     .  343 
Oil  testing  .     .     .     .     .     .344 

Shale  oil  industry     ....  345 

Ozokerite 346 

Asphalt 347 

VEGETABLE  AND  ANIMAL  OILS,  FATS 

AND  WAXES 

Properties  of  the  fatty  oils  .  349 
Hydrolysis  of  fats  .  .  .  .351 
Occurrence  and  extraction  of 

the  vegetable  oils      .     .     .  352 
Occurrence  and  extraction  of 

the  animal  oils  .  ,.  .  .  354 
Testing  of  fatty  oils  .  .  .355 
Classification  of  oils  .  .  .  356 
Vegetable  drying  oils  .  .  357 
Vegetable  semi-drying  oils  359 
Vegetable  non-drying  oils  .  362 
Marine  animal  oils  .  .  .  363 
Terrestrial  animal  oils  .  .  365 
Solid  vegetable  fats  .  .  .  366 
Solid  animal  fats  ....  367 

Waxes 368 

Liquid  waxes 368 

Solid  animal  waxes   .     .     .  369 
Solid  vegetable  wax  .     .     .  370 

SOAP 

Saponification 372 

Soap  kettles 374 

Cold  process  soap  ....  374 
Boiled  soaps 375 


Yellow  (rosin)  soaps 
"Boiled  down  soaps" 
Toilet  soaps     .     .     . 
Milled  soaps      .     . 
Remelted  soaps 
Transparent  soaps 
Scouring  soaps      .     . 
Soap  powder    . 


PAGE 

.  375 
.  377 

.  378 
.  378 
.  378 
.  378 
.  379 
.  379 


CANDLES 

Dipped,  poured,  and  moulded 

candles 380 

Saponification  of  fats  for 
candle  stock 381 

GLYCERINE 

Van  Ruymbeke  process  for 
recovery  of  glycerine  from 
spent  soap  lyes  ....  384 

Glycerine  from  candle  stock   .  385 

Glatz  process  for  glycerine 
from  soap  lyes  ....  385 

Properties  and  uses  of  glyc- 
erine   386 

ESSENTIAL  OILS 

Properties,   and   methods   of 

extraction, 387 

Characteristics  of  the  in- 
dividual essential  oils  388-392 

RESINS  AND  GUMS 

Resins 393-396 

Varnishes,  spirit,  turpen- 
tine, and  linseed  oil  var- 
nish   397 

Oleo-resins 398 

Balsams 398 

Gum-resins,  properties  of  the 
individual  gum-resins  398-399 

Gums,  properties  of  the  in- 
dividual gums .  .  .  399-400 

STARCH,  DEXTRIN,  AND  GLUCOSE 
Occurrence  and  properties  of 

starch.     .     .     ,v    .     .     .  401 

Corn  starch 402 

Wheat  starch 407 

Potato  starch 408 

Rice  starch       .     .     .     .     .409 
.  410 


XV111 


TABLE   OF   CONTENTS 


PAGE 

Arrowroot 410 

Cassava 411 

Dextrin 412 

Manufacture  of  dextrin  and 
British  gum       ....  412 

Glucose 412 

Dextrose,     levulose,     and 

commercial  glucose     .  413 

1    Conversion 414 

Neutralization  ....  415 
Bone-char  nitration    .     .  416 

CANE  SUGAR 

Occurrence  and  properties  of 

cane  sugar 420 

Manufacture  of  raw  sugar 

from  sugar  cane     .     .     .421 
Manufacture  of  raw  sugar 

from  sugar  beets    .     .     .  425 
Sugar  refining 428 

FERMENTATION  INDUSTRIES 

Fermentation 435 

Organized  ferments,  mould 
growths,  bacteria,  yeast     435 

Wine 440 

Composition  of  grape  juice  440 
Extraction  of  the  must .     .  440 
Fermentation  of  the  must  .  441 
Clarification  and  preserva- 
tion of  the  wine     .     .     .  442 
"Improving"  of   the   new 
wine    .     ....     .     .  443 

Champagne      .....  443 

Other  wines 444 

Brewing 444 

Malting 445 

Steeping,   couching,  and 

flooring 446 

Pneumatic  malting     .     .  447 

Mashing 448 

Infusion  method    .     .     .  449 

Decoction  method      .     .  450 

Boiling  of  the  wort   .     .     .  451 

Hops 451 

Cooling  of  the  hot  wort      .  452 
Fermenting  of  the  wort  .     .  452 
' '  Vacuum    process ' '     of 
fermentation      .          .  454 


PAGE 

Extract  in  beer     ....  454 

Bottling  or  barrelling     .     .  454 

Brewed  liquors      ....  455 

Distilled  liquors 456 

Manufacture  of  alcohol      .  456 
Distillation    of    the    fer- 
mented mash     .     .     .  458 
Purification    and    recti- 
fication of  raw  spirit     .  459 
Revenue  restrictions 

upon  the  industry   .     .  459 
Denatured  alcohol, 

"  methylated  spirit  "  .  460 

Fusel  oil 461 

Whiskey 461 

Gin 462 

Brandy 462 

Rum  . 463 

Liqueurs,  cordials,  arrack, 

absinthe 463 

Vinegar 463 

Orleans  process  of  manu- 
facture       464 

"  Quick  "  vinegar  proces^    .  465 
Cider,     wine,     malt,     and 

spirit  vinegars  ....  466 
Lactic      fermentation      and 

lactic  acid 467 

EXPLOSIVES 

Characteristic    properties    of 

explosives 470 

Gunpowder 471 

Pebble     and     prismatic 

powders 474 

Brown  or  cocoa  powder  .  475 

Mining  powders     .     .     .  475 

Nitrocellulose  or  guncotton  475 

Pyroxyline    .....  479 

Nitroglycerine       ....  479 

Dynamite     .     .     ..     .     .481 

Explosives  with  an  active 

"dope" 482 

Forcite 483 

Blasting     gelatine     and 

gelatine  dynamite  .     .  483 

Smokeless  powders     .     .  483 

Picrates  and  picric  acid  .     .  484 


TABLE   OF  CONTENTS 


XIX 


Fulminates    and    fulminic 
acid 484 

Azides  of  heavy  metals  as 
detonators 484 

Sprengel  explosives   .     .     .  485 

Military  explosives   .     .     .  485 
Melinite,     lyddite,     shi- 
mose,  trinitrotoluol     .  485 

TEXTILE  INDUSTRIES 

Fibres .487 

Vegetable  fibres    .     .     .     .487 

Cotton  fibre 487 

Mercerized  cotton  .     .  489 
Alkali  cellulose,   "vis- 
cose"      490 

Linen 490 

Hemp 491 

Jute 491 

China  grass  (ramie]    .     .  492 

Esparto 492 

Manila,  sisal,  and  sunn 

hemp 492 

Cocoanut  fibre  ....  492 

Animal  fibres 492 

Silk 492 

Artificial  silk      .     .     .496 

Wool 497 

Wool  scouring  and  re- 
covery      of       wool 

grease 499 

Carbonizing    of    vege- 
table fibre  in  wool  501 

Bleaching 501 

Cotton  bleaching       .     .     .501 
Madder  bleach  for  calico 

print  cloth     ....  503 
Turkey-red    bleach    for 
cotton  to  be  dyed  with 

alizarins 506 

Market  bleach  for  com- 
mercial white  goods    .  506 
Mather-Thompson    pro- 
cess for  bleaching  .     .  507 
Hermite  bleaching   pro- 
cess   508 

Hydrogen  peroxide  and 
permanganates  as  cot- 
ton bleaches  .  .  508 


Linen  bleaching    ....  508 
Irish  process      ....  508 
Jute  bleaching      ....  509 
Hemp  bleaching   ....  509 
Wool  bleaching     .     .     .     .510 
Stretching   of   yarn   be- 
fore      scouring      and 

bleaching 510 

"Crabbing"     of     union 

goods 510 

Stoving 511 

Hydrogen  peroxide 

bleach 512 

Silk  bleaching 512 

Mordants 512 

Metallic  mordants  .  .  .  513 
Organic  mordants,  .  .  .  518 

Tannins 518 

Coloring  matters      .     .     .     .521 
Natural  dyestuffs      .     .     .521 
Artificial  dyestuffs     .     .     .  526 
Relation  of  color  to  con- 
stitution     527 

Dyeing .528 

Theories     of     the     dyeing 

process 529 

Methods  of  dyeing  textiles  530 
Grouping     of    commercial 
dyes      according      to 
method  of  application 
to  the  fibre    .     .     .     .531 

Direct  dyes 532 

Basic  dyes 533 

Acid  dyes 535 

Mordant  dyes  ....  536 
Acid-mordant  dyes  .  .  539 
Sulphide  dyes  ....  540 

Vat  dyes 541 

Ingrain  colors   ....  543 

Textile  printing 546 

Block  printing  ....  546 
Machine  printing  .  .  .  547 
Color  mixing  .  .  .  .  .  548 

Styles 549 

Pigment  style   ....  549 

Steam  style 549 

Madder  style  ....  550 
Oxidation  style  .  .  .  550 


XX 


TABLE  OF  CONTENTS 


PAGE 

Discharge  style      .     .     .  550 

Resist  style 551 

Wool  printing 551 

Silk  printing 551 

PAPER 

Materials  for  paper       .     .     .  554 

Wood  pulp  .     .     .  •  .     .     .  554 

Mechanical  pulp    .     .     .  554 

Chemical  pulp       .     .     .  555 

Soda  process       .     .     .  555 

Sulphite  process      .     .  555 

Sulphate  process     .     .  558 

Rags 561 

Esparto 561 

Jute 562 

Bleaching  of  paper  pulp    .     .  562 
Paper  making  process  .     .     .  562 

Furnishing        563 

Sizing 563 

Hand-made  paper     .     .     .  564 

Cylinder  machine      .     .     .  564 

Fourdrinier  machine      .     .  564 

Printing  paper       .     .     .  565 

Wrapping  paper    .     .     .  565 

Writing  paper  ....  565 

Blotting       and       tissue 

papers 565 

Parchment  paper  .  .  .  565 
Willesden  paper  .  .  .  566 
Vulcanized  fibre  .  .  .  566 

GLUE 

Colloidal    characteristics    of 

glue 568 

Sources  of  glue 568 

Preparation  of  glue  .     .     .  568 

Hide  glue 568 

Bone  glue 570 

Fish  glue 570 

Liquid  glue 570 

Gelatine 570 

Isinglass 571 

Vegetable  gelatine  (agar  agar)  571 

LEATHER 

Structure  of  the  skin      .     .     .  572 
Hide  substance  considered 
as  a  gel 573 


Classification  of  pelts   .     .     .  573 

^reparation  of  the  skins    .     .  574 

Depilation  processes      .     .  575 

Liming 575 

Sweating 575 

Beaming 576 

Bating 576 

Tanning  processes    ....  577 
With     tannins     (vegetable 

tannage) 577 

Sole  leather 578 

Upper  leather   ....  578 

Currying 579 

Colored  leathers    .     .     .  579 

Split  leathers  (skivers)     .  579 

Tawing  (mineral  tannage)  580 

Chrome  tannage    .     .     .  580 
Combination       tannage 

(dongola  process)    .     .  580 
Tanning  with  oils      .     .     .581 

Degras 581 

Sod-oil 581 

Morocco  leather       ....  582 

Russia  leather 582 

Patent  leather 582 

Parchment  and  vellum       .     .  582 

Artificial  leather 583 

Theory  of  tanning    ....  583 

PLASTICS 

Celluloid 584 

Cellulose  acetate  ....  585 

Bakelite    .  .     .  , 585 

Galalith 586 

Caoutchouc  or  India  rubber  .  586 
Sources  of  crude  rubbers    .  586 
Synthetic  rubber  ....  587 
Preparation  of  crude  rub- 
bers for  manufacturing    .  587 
Preparation       of       rubber 
"compound"    ....  588 

Vulcanizing 588 

Reclaimed,    recovered,    or 

devulcanized  rubber  .     .  589 

Rubber  substitutes  ....  589 

Rubber  cement 591 

Ebonite,  hard  rubber,  or  vul- 
canite        591 

Gutta-percha 591 


TABLE   OF   CONTENTS 


XXI 


PART  III 

METALLURGY 


METALLURGICAL  PROCESSES 

Ore  dressing 593 

Wet  processes 593 

Dry  processes 593 

ROASTING 

Oxidizing  roast    .....  594 

Sulphatizing  roast    ....  594 

Chloridizing  roast     ....  594 

Reverberatory  furnace  .     .  595 

Ropp  furnace 596 

McDougal  furnace    .     .     .  597 

Howell-White  furnace         .  598 

Shaft  furnace 599 

Heap  roasting 599 

StaU  roasting .599 

Dwight-Lloyd  sintering  ma- 
chine .     t ; » /  * .    .     .     .     .  600 

IRON  AND  STEEL 

Ores  of  iron     ."V    .  •  V-. .     .  601 
Blast  furnace  for  iron  .     .     .601 
Chemistry    of    the    blast- 
furnace process      .     .     .  602 
Pig  iron      .  '.  ;.     .     ,     .     .  604 
Wrought  iron   :.../.,.     .  604 
Steel       .     .     .  -,     ....  605 
Bessemer  process ....  605 
Acid  process      ....  606 
Basic  process    ....  607 
Open  hearth  process      .     .  607 
Campbell  furnace  .     .     .  608 
Monell  process       .     .     .  609 
Crucible  process   ....  609 
Cementation  process      .     .  609 

Special  steels 610 

Electrical  methods  for  steel 
making 610 

COPPER 

Ores  of  copper 611 

Reverberatory  smelting      .  611 
Blast-furnace  smelting  .     .  613 
Comparison     of     rever- 
beratory     and     blast- 
furnace .615 


Copper  converting    .     .     .  615 
Leaching  processes  for  cop- 
per   616 

Longmaid  process  .  .  617 
Copper  refining  .  .  .  .617 
Properties  and  uses  of 

copper      .     .     .     .     .     .  618 

LEAD 

Ores  of  lead 618 

Blast-furnace    smelting    of     , 
lead 619 

Reverberatory  smelting  of 
lead 620 

Ore  hearth  for  lead  smelt- 
ing   620 

Refining  of  lead  .  .  .  .620 
Parkes'  process  .  .  .621 
Pattinson's  process  .  .  622 
Cupellation  .  .  .  .  .622 

Properties  and  uses  of  lead  .  622 

ZINC 

Ores  of  zinc 623 

Reduction  of  zinc  in  clay 

retorts 623 

Refining  of  crude  zinc    .     .  624 
Properties  and  uses  of  zinc  .  625 

CADMIUM 

Occurrence     and     extraction 

from  its  ores      .     .    ' .     . 

Properties     and     uses     of 

cadmium  .     . 


625 
625 

626 
626 
627 


TIN 

Occurrence  of  tin  ore  . 
Smelting  of  tin  .  . 
Refining  of  crude  tin 

SILVER 

Ores  of  silver 628 

Direct  extraction  of  silver 

from  its  ore  ....  628 
Cyanide  process  .  .  .  628 
Amalgamation  .  .  .  628 
Patio  process  ....  628 


XX11 


TABLE   OF  CONTENTS 


Washoe  process 
Reese  River  process 
Leaching  processes 


PAGE 

629 
629 
629 


GOLD 

Ores  of  gold 630 

Extraction  of  gold  from  its 

ores 630 

Placer  working       .     .     .  630 
Amalgamation  ....  630 
Cyanide  process     .     .     .631 
Precipitation    of    gold 
from   cyanide   solu- 
tion with  zinc      .     .  632 
Siemens-Halske     elec- 
trical    method     of 
precipitation  .     .     .  633 
Betty-Carter     process 

of  precipitation  .     .  633 
Chlorination   process   of 

extraction      ....  633 
Parting  of  gold  and  silver 

by  use  of  acids  .  .  .  634 
Miller  process  of  parting  635 
Wohlwill  electrical 

method  of  parting  .  .  635 
Moebius  electrical  pro- 

.  636 


PLATINUM 

Occurrence      and      ores     of 

platinum 636 

Extraction  and  refining  .     .  636 
Properties     and     uses     of 
platinum 637 

MERCURY 

Ore  and  extraction  of  mer- 
cury   637 

ALUMINUM 

Production  by  use  of  the 
electric  furnace  ....  638 

Bauxite  as  a  source  of  alu- 
minum   639 

Properties  and  uses  of  alu- 
minum   639 

Alloys  of  aluminum  ....  639 


NICKEL 

Ores  of  nickel 640 

Extraction  of  nickel  from 

its  ores 640 

Orford  process  ....  640 
Mond  process    ....  640 
Browne  electrolytic  pro- 
cess   641 

Blast-furnace      smelting 

of  garnierite  ....  642 
Properties     and     uses     of 
nickel 642 

SODIUM 

Production  by  electrolysis  of 
fused  caustic  soda  .  .  .  643 

ARSENIC 

Occurrence  and  extraction 
from  its  ores 643 

ANTIMONY 

Occurrence  and  extraction     .  644 

BISMUTH 

Occurrence  and  ores  of  bis- 
muth       .     .  645 

Extraction  and  refining  of 

the  metal 645 

Properties  and  uses  of  bis- 
muth   645 

MAGNESIUM 

Production  by  electrolysis 
from  carnallite  ....  646 

Properties  and  uses  of  mag- 
nesium   646 

Magnalium 646 

ALLOYS 

Properties    and    constitution 

of  alloys 646 

Preparation  of  alloys     .     .  647 

Brass 647 

Bronze 647 

Bearing  metal  or  Babbitt 

metal 647 

Solders 648 

Type  metal 648 

Fusible  alloys    .     .     .     .648 
Coins  .  .  648 


GENERAL  REFERENCES   ON  INDUSTRIAL 
CHEMISTRY 


Chimie  Industrielle.     A.  Payen.     Paris,  1867. 

Grundriss  der  chemischeri  Technologie.     H.  Post. 

Abriss  der  chemischen  Technologie.    C.  Heinzerling.   Berlin,  1888.    (T.  Fischer.) 

Trait^  de  Chimie  applique"e  a  1'Industrie.    Adolphe  Renard.     Paris,  1890. 

Handbuch  der  chemischen  Technologie.     Dr.  0.  Dammer.     5  Vols.     Vol.  I, 

1895.     Vol.  II,  1895.     Vol.  Ill,  1896.     Stuttgart.     (F.  Enke.) 
Chemical  Technology.     R.Wagner.     Translated  by  Wm.  Crookes.     New  York, 

1897.     (D.  Appleton  and  Co.) 
Encyclopaedisches    Handbuch   der   technischen   Chemie.      F.    Stohmann  und 

Bruno  Kerl.     Vol.  I,  1888.     Vol.  II,  1889.     Vol.  Ill,  1891.     Vol.  IV,  1893. 

Vol.   V,    1896.     Vol.    VI,    1898.      Vol.    VII,    1900.     Braunschweig.     (F. 

Vieweg.) 
Chemical    Technology.       Edited    by    C.    E.    Groves    and    William    Thorp. 

Vol.  I,  Fuel,  1889.     Vol.  II,  Lighting,  1895.     Vol.  Ill,  Gas  Lighting,  1900. 

Vol.  IV,  Electric  Lighting,  1903. 
Handbuch   der   chemischen   Technologie.     Dr.    Ferdinand   Fischer.     2   Vols. 

Vol.  I,  1900.     Vol.  II,  1902.     Leipzig.     (O.  Wigarid.) 

Lehrbuch  der  chemischen  Technologie.     Dr.  Ferdinand  Fischer.     Leipzig,  1903. 
Handbook  of  Chemical   Engineering.     G.  E.  Davis.     2d  ed.    2  Vols.     Man- 
chester, 1905. 

Trait6  Chimie  Applique"e.    C.  Chabrie.    2  Vols.    Paris,  1905.     (Masson  et  Cie.) 
Chemische  Technologie  der  Neuzeit.    Edited  by  O.  Dammer.    3  Vols.     Stuttgart, 

1910.     (Enke.) 
Chemistry   for   Engineers  and   Manufacturers.      Bertram  Blount  and  A.    G. 

Bloxam.     2  Vols.     London,  1905.     (Griffin  and  Co.) 
Modern  Industrial  Chemistry.     H.  Bluecher.     Translated  by  J.  P.  Millington. 

New  York,  1911.     (Stechert  &  Co.) 
Handbook   of  Industrial   Organic   Chemistry.     S.    P.    Sadtler.     Philadelphia. 

4th  ed.     1912.     (J.  B.  Lippincott.) 
A  Dictionary  of  Applied  Chemistry.    T.  E.  Thorpe.     2d  ed.     5  Vols.    London, 

1912-13.     (Longmans,  Green  and  Co.) 
Vorlesungen    iiber    Chemische   Technologie.      Dr.    H.  Wichelhaus.     3tc   Auf. 

Dresden,  1912.     (Steinkopff . ) 
Lehrbuch  der  Chemischen  Technologie  und  Metallurgie.    Edit,  by  B.  Neumann. 

Leipzig,  1912.     (S.  Hirzel.) 
General  and  Industrial  Chemistry.     E.  Molinari.     2  Vols.    Translated  by  E. 

Feilmann.     Philadelphia,  1912.     (Blakiston's  Sons  Co.) 

Lehrbuch  der  technischen  Chemie.     H.  Ost.     8th  ed.    Leipzig,  1914.    (Janecke.) 
Industrial  Chemistry.     Chapters  by  Specialists.     Edited  by  A.  Rogers  and  A.  B. 

Aubert.     New  York.     2d  ed.     1915.     ( Van  Nostrand  Co. ) 

xxiii 


ABBREVIATIONS  OF  THE  NAMES  OF  JOURNALS 

FREQUENTLY    OCCURRING    IN    THE    LITERATURE    OF    INDUSTRIAL   CHEMISTRY 

A.  or  Ann.  =  Annalen  der  Chemie  und  Pharmacie,  by  Liebig  and  others,  1832  -f . 

Ann.  chim.  phys.  =  Annales  de  Chimie  et  de  Physique.     Paris,  7  series,  1789  +  . 

Ber.  =  Berichte  der  deutschen  chemischen  Gesellschaf t.     Berlin,  1868  + . 

Bull.  Soc.  Chim.  =  Bulletin  des  Seances  de  la  Socie'te'  chimique  de  Paris, 
2  series,  1864  + . 

Chem.  Centralb.  =  Cheinisches  Centralblatt.    4  series,  1829  +. 

Chem.  Ind.  =  Zeitschrift  fur  die  chemische  Industrie.     1878  +  . 

C.  N.  or  Chem.  N.  =  Chemical  News.     1860  + . 

C.  R.  or  Compt.  rend.  =  Coinptes-rendus  hebdornadaires  des  Seances  de  1' Acade- 
mic des  Sciences.  Paris,  1835  +. 

Chem.  Zeit.  =  Chemiker-Zeitung.     1877  +. 

Dingl.  J.  =  Dingler's  poly technisches  Journal.     1820  +  . 

Electrochem.  Ind.  =  Electrochemical  Industry.     1902  -f  1909. 

Eng.  Min.  Jour.  =  Engineering  and  Mining  Journal.     1866  +. 

Jahresb.  =  Jahresbericht  tiber  die  Fortschritt  der  Chemie,  u.  s.  w. 

J.  Am.  Chem.  Soc.  =  Journal  of  the  American  Chemical  Society.  New  York, 
1879  +. 

J.  Chem.  Soc.  =  Journal  of  the  Chemical  Society  of  London.     1849  +  . 

J.  Ind.  Eng.  Chem.  =  Journal  of  Industrial  and  Engineering  Chemistry.    1909  -f. 

J.  Soc.  Chem.  Ind.  =  Journal  of  the  Society  of  Chemical  Industry.  London, 
1882  +. 

Met.  Chem.  Eng.  =  Metallurgical  and  Chemical  Engineering.     1909  +. 

Trans.  Am.  Inst.  Chem.  Eng.  =  Transactions  of  the  American  Institute  of 
Chemical  Engineers.  1908  + . 

Trans.  Am.  Inst.  Elect.  Eng.  =  Transactions  of  the  American  Institute  of  Elec- 
trical Engineers.  1884  +• 

Trans.  Am.  Inst.  Min.  Eng.  =  Transactions  of  the  American  Institute  of  Mining 
Engineers.  1871  +. 

Trans.  Am.  Electrochem.  Soc.  =  Transactions  of  the  American  Electrochemical 
Society.  1902  +. 

W.  J.  =  Wagner's  Jahresbericht  der  chemischen  Technologie.     1855  +. 

Zeitschr.  angew.  Chem.  =  Zeitschrift  fur  angewandte  Chemie.     Berlin,  1887  +. 

Zeitschr.  anorg.  Chem.  =  Zeitschrift  fur  anorganische  Chemie.     1892  +. 

Zeitschr.  Chem.  Ind.  =  Zeitschrift  fur  die  chemische  Industrie.     1887  +. 

Zeitschr.  Elektrochem.  =  Zeitschrift  fur  Elektrochemie.     1894  +. 

Zeit.  physikal.  Chem.  =Zeitschrift  fur  physikalische  Chemie.     1887  +. 


xxiv 


RELATION   BETWEEN  WEIGHTS   AND 
MEASURES 


1  linear  inch 

2.54 

centimeters. 

1  linear  foot 

=          .3048 

meter 

1  linear  yard 

=          .914 

meter 

1  linear  mile 

=  1609. 

meters 

FREQUENTLY    OCCURRING    IN    THE    LITERATURE    OF    INDUSTRIAL    CHEMISTRY 


=  30.48  centimeters. 
=  91.44  centimeters. 
=  1.609  kilometers. 


1  cubic  inch  =      16.387        cubic  centimeters. 

1  cubic  foot  =        7.48         gallons  =  28.315. 

1  cubic  foot  of  water  at  16.5°  C.  weighs  62.355  pounds. 

1  fluid  ounce  =      29.574       cubic  centimeters. 

1  quart  =    946.6  cubic  centimeters. 

1  gallon  U.S.  =    231.  cubic  inches  =  3.7854  liters. 

1  gallon,  U.S.,  of  water  at  16.5°  C.,  weighs  8.3356  pounds. 


1  grain 

1  ounce  Avd. 

1  pound  Avd. 

1  ounce  Apoth.  = 

1  centimeter  = 

1  meter  = 

1  kilometer  = 

1  liter 

1  hektoliter  = 

1  gram  = 

1  kilogram  = 

1  cubic  centimeter  = 

In  solutions, 

1  grain  per  gallon  = 

1  grain  per  gallon  x 

1  gram  per  liter  = 

1  gram  per  liter  = 


.064799  gram. 
28.3495      grams. 
7000.  grains  =  453.593       grams. 
31. 103       grams. 


.39370 
39.37 
.621 


inch. 

inches. 

mile. 


1.057  quarts  =  61.023  cubic  inches. 

26.425  gallons. 

15.432  grains. 

2.2046  pounds  Avd.  =  35.274  ounces. 


.034 


fluid  ounce      =      .272  dram. 


.017118  gram  per  liter. 
17.1  =  parts  per  million. 

.008345  pound  per  gallon  =  68.42  grains  per  gallon. 
.06242    pound  per  cubic  foot. 


xxv 


OUTLINES  OF  INDUSTRIAL  CHEMISTRY 


PART  I 
INORGANIC  INDUSTRIES 


INTRODUCTION 

INDUSTRIAL  chemistry  deals  with  the  preparation  of  products  from 
raw  materials,  through  the  agency  of  chemical  change.  But  there  is 
an  occasional  exception  to  this  definition ;  for  a  few  industries,  de- 
pending on  strictly  mechanical  changes,  are  classed  among  the  chemical 
industries.  Since  a  sharp  line  cannot  be  drawn  between  chemical 
and  mechanical  technology,  a  study  of  the  former  necessarily  involves 
some  consideration  of  the  mechanical  appliances  and  apparatus,  by 
means  of  which  the  chemical  reactions  are  carried  ou.t. 

The  products  of  chemical  industry  are  exceedingly  numerous  and 
varied  in  character,  but  comparatively  few  come  into  the  hands  of 
the  mass  of  the  people  for  direct  consumption.  Many  of  them  are 
used  only  in  making  other  substances,  for  it  is  often  the  case  that 
the  finished  product,  by-product,  or  waste  from  one  industry  be- 
comes the  raw  material  for  another,  and  it  rarely  happens  that  one 
manufacturer,  starting  with  the  raw  materials  found  in  nature,  pro- 
duces from  them  articles  for  popular  use.  Thus  the  chemical  industries 
become  a  network  of  interlacing  processes,  and  in  considering  one 
it  is  often  difficult  to  separate  it  from  others  which  have  a  more  or 
less  direct  bearing  upon  it.  Furthermore,  as  competition  has  become 
very  close  in  many  lines,  the  use  which  may  be  made  of  by-products 
and  waste  is  so  important,  that  processes  are  often  carried  out  with  the 
view  of  obtaining  larger  yields  or  better  quality  of  the  by-products, 


2  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

which  may  have  become  a  source  of  considerable  profit.  In  a  few 
instances,  it  might  be  said  that  what  were  originally  the  by-products 
are  now  the  chief  products  and  main  support  of  these  particular 
industries.  This  is  especially  true  in  the  case  of  the  Leblanc  Soda 
Industry,  which  would  long  since  have  been  abandoned  were  it  not 
for  its  production  of  hydrochloric  acid.  The  utilization  of  waste 
materials  furnishes  an  almost  inexhaustible  subject  for  investiga- 
tion by  the  industrial  chemist. 

The  manipulations  of  most  frequent  occurrence  in  the  various 
processes  are  here  defined  and  explained  for  the  sake  of  brevity  in 
the  text. 

LIXIVIATION 

Lixiviation  is  the  process  of  separating  soluble  from  insoluble 
substances  by  dissolving  the  former  in  water  or  some  other  solvent. 
The  mixture  of  substances  is  put  into  a  suitable  vessel,  the  solvent 
poured  over  it,  and  the  whole  allowed  to  stand  until  a  strong  solu- 
tion is  obtained,  which  is  then  drawn  off  from  the  residue.  This 
process  is  repeated  as  often  as  necessary,  until  the  desired  amount 
of  soluble  matter  has  been  removed.  Sometimes  the  mixture  is  put 
into  baskets,  or  on  gratings,  which  are  suspended  in  tanks  of  water. 
The  solution  being  denser  than  the  solvent  sinks  to  the  bottom  as  it 
forms,  and  water  comparatively  free  from  dissolved  material  is  thus 
constantly  brought  into  contact  with  the  substance  to  be  lixiviated. 
The  insoluble  substance  remains  on  the  grating  or  in  the  baskets. 
When  desired,  the  soluble  material  may  be  recovered  from  the  solu- 
tion by  evaporation  or  precipitation.  Extraction  is  the  term  usually 
employed  when  some  solvent  other  than  water  is  used  in  lixiviating. 
Thus  we  speak  of  extraction  by  steam,  alcohol,  carbon  disulphide,  etc. 

LEVIGATION 

Levigation  is  the  process  of  grinding  an  insoluble  substance  to  a 
fine  powder,  while  wet.  The  material  is  introduced  into  the  mill 
together  with  water,  in  which  the  powdered  substance  remains  sus- 
pended, and  flows  from  the  mill  as  a  turbid  liquid  or  thin  paste, 
according  to  the  amount  of  water  employed.  There  is  no  loss  of 
material  as  dust,  nor  injury  or  annoyance  to  the  workmen.  Further, 
any  soluble  impurities  in  the  substance  are  dissolved,  and  the  prod- 
uct thereby  purified.  The  greatest  advantage  of  this  process  is  the 
facility  it  affords  for  the  subsequent  separation  of  the  product  into 


INTRODUCTION  3 

various  grades  of  fineness,  because  of  the  slower  subsidence  of  the  finer 
particles  from  suspension.  The  turbid  liquid  flows  into  the  first  of 
a  series  of  tanks,  and  is  allowed  to  stand  for  a  certain  time.  The 
coarsest  and  heaviest  particles  quickly  subside,  leaving  the  finer 
material  suspended  in  the  water,  which  is  drawn  from  above  the 
sediment  into  the  next  tank.  The  liquid  is  passed  from  tank  to 
tank,  remaining  in  each  longer  than  it  remained  in  the  preceding, 
since  the  finer  and  lighter  the  particles,  the  more  time  is  necessary 
for  their  deposition.  In  some  cases  a  dozen  or  more  tanks  may  be 
used,  and  the  process  then  becomes  exceedingly  slow,  as  very  fine 
slimes  or  muds  may  require  several  weeks  for  the  final  settling.  But 
as  a  rule,  from  three  to  five  days  is  sufficient. 

The  term  "  levigation  "  is  now  often  applied  to  mere  sedimenta- 
tion, a  substance  being  simply  stirred  up  in  water,  without  previous 
wet-grinding,  in  order  to  separate  the  finer  from  the  coarser  parti- 
cles, as  above. 

EVAPORATION 

Evaporation,  in  a  technical  sense,  denotes  the  conversion  of  a 
liquid  into  a  vapor  for  the  purpose  of  separating  it  from  another 
liquid  of  higher  boiling  point,  or  from  a  solid  which  is  dissolved  in 
it.  In  the  great  majority  of  cases,  the  liquid  evaporated  is  water. 
If  the  liquid  evaporated  is  to  be  recovered,  the  vapors  are  condensed, 
and  the  process  then  becomes  one  of  Distillation  (see  p.  9). 

There  are  four  general  methods  of  evaporation  :  — 

1.  Spontaneous  evaporation  in  the  open  air. 

2.  Evaporation  by  application  of  heat  directly  from  a  fire  to 
the  vessel  containing  the  liquid. 

3.  Evaporation  by  indirect  application  of  heat  from  the  fire,  as  ^ 
by  means  of  steam,  with  or  without  pressure. 

4.  Evaporation  under  reduced  pressure. 

The  first  method,  by  spontaneous  evaporation  in  the  open  air,  is 
comparatively  slow,  and  requires  exposure  of  very  large  surfaces  of 
liquid.  The  time  necessary  depends  Upon  the  temperature  and 
humidity  of  the  air,  and  the  completeness  with  which  the  vapors 
are  removed  from  the  surface  of  the  liquid;  hot,  dry  weather,  es- 
pecially if  a  brisk  wind  is  blowing,  evaporates  water  quite  rapidly. 
This  process  is  only  used  for  the  manufacture  of  salt  from  sea  water, 
or  from  natural  brines.  In  certain  warm  countries  considerable 
quantities  of  salt  are  thus  prepared,  and  in  this  country  some  is  made 
from  a  brine  found  near  Syracuse,  N.Y.  Sometimes  weak  brines 


FIG.  1. 


4  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

are  allowed  to  trickle  in  fine  streams  over  tall  piles  or  "  ricks  "  of 
brushwood  in  the  open  air.  The  liquid  being  so  exposed  in  thin 
layers,  to  the  air  and  wind,  is  concentrated  to  such  a  degree  that  it 
will  pay  to  complete  the  evaporation  by  artificial  heat. 

The  second  method,*  by  direct  application  of  heat  from  a  fire,  is 
very  largely  used  in  the  arts.  This  may  be  done  in  two  general 
ways :  — 

(a)  The  flames,  or  hot  gases  from  the  fire,  are  generally  allowed 
to  play  directly  on  the  bottom  of  the  vessel  containing  the  liquid; 

or  they  may  pass  through 
flues  or  pipes,  set  into  the 
vessel,  so  that  the  liquid 
surrounds  them  on  all  sides 
(Fig.  1).  Such  pans  are 
often  several  yards  in 
length,  and  may  contain 

one  large  flue,  or  several  small  ones,  according  to  the  work  desired; 

but  this  form  of  apparatus  is  expensive  to  build,  and  difficult  to  keep 

in  repair. 

(b)  The  flames  and  hot  gases  may  be  conducted  over  the  surface 
of  the  liquid  to  be  evaporated.     This  mode  is  only  used  for  coarse 
and  common  products,  or  in  the  concentration  or  recovery  of  waste 
materials.     But  it  has  the  advantage  that  the  bottom  of  the  pan  is 
less  liable  to  be  injured  by  the  crusting  of  a  precipitate  upon  it. 
Another  point  often  in  favor  of  surface  heating  is  that  the  liquid  is 
evaporated  in  a  reducing  atmosphere.     But  as  flue  dust  and  ashes 
are  liable  to  fall  into  the  pans,  the  product  is  usually  impure.     Large 
shallow  pans  are  used,  which  are  generally  arched  over  with  brick, 
in  order  that  the  heat  may  be  better  utilized,  through  radiation  from 
the  brick  walls.     There  are 

various  ways  of  setting  the 
pans  for  this  process ;  a  simple 
method  is  shown  in  Fig.  2.  A 
modification  of  this  method  is 
the  use  of  a  long  cylinder,  set 
at  a  slight  incline,  and  revolv- 
ing about  its  longitudinal  axis  (Fig.  3).  The  lower  end  is  open  for 
the  entrance  of  the  flames  and  gases  from  the  grate  (A),  which  pass 
through  the  cylinder  (B),  on  their  way  to  the  chimney  (D).  The  hot 


FIG.  -2. 


*  To  save  expense,  the  waste  heat  from  calcination  or  furn-acing  operations  is 
frequently  utilized. 


INTRODUCTION  5 

gases  are  often  passed  through  the  flues  of  a  boiler  (C),  to  utilize  the 
waste  heat.  The  solution  to  be  evaporated  is  fed  into  the  cylinder 
at  the  upper  end  in  a  small  stream,  and  comes  in  direct  contact  with 
the  flame.  The  water  is  evaporated,  and  the  solid  matter  is  deliv- 
ered into  the  pit  or  wagon  (E)  at  the  lower  end  of  the  furnace,  in  a 


FIG.  3. 

dry  and  calcined  state.  Such  furnaces  are  frequently  used  for  evapo- 
rating waste  liquors  to  recover  the  salts  which  they  contain ;  and  for 
the  treatment  of  sewage  and  other  liquid  refuse. 

The  third  method  of  evaporation,  by  the  use  of  steam  heat,  is 
very  often  employed  where  there  is  danger  of  injury  to  the  product 
by  overheating. 

(a)  Jacketed  pans  or  kettles  may  be  used.  These  are  simply 
double-walled  vessels,  the  steam  being  admitted  between  the  walls. 

(6)  The  steam  may  be  allowed  to  circulate  through  coils  of  pipe, 
placed  inside  the  vessel,  which  is  sometimes  made  of  wood.  The 
temperature  of  the  liquid  depends  on  the  steam  pressure ;  very  often 
exhaust  steam  is  employed. 

The  fourth  method,  evaporation  in  vacua,  is  merely  a  modifica- 
tion of  either  the  second  or  third  method,  but  is  considered  sepa- 
rately for  convenience.  The  boiling  point  of  a  liquid  may  be  very 
materially  lowered  by  reducing  the  pressure  within  the  vessel.  Hence, 
solutions  containing  substances  which  would  be  injured  by  the  heat 
necessary  to  boil  them  under  the  atmospheric  pressure,  or  liquids 
boiling  at  very  high  temperatures,  are  evaporated  in  vacuum  pans. 

The  different  forms  of  apparatus  used  for  vacuum  evaporation 
vary  much  in  their  details,  but  all  depend  on  the  principle  of  re- 
duced pressure.  The  essential  parts  of  the  plant  are  the  vacuum 
pan  or  still,  the  pump  for  exhausting  the  air  and  steam  from  the 
pan  and  sending  them  to  the  condenser,  and  the  heating  apparatus. 
The  vacuum  pan  is  usually  a  globular  copper  or  iron  vessel,  pro- 
vided with  a  manhole,  a  pressure  gauge,  and  a  discharging  valve. 
Very  often  a  piece  of  heavy  plate  glass  is  set  in  the  side  to  afford  a 


6  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

view  of  the  interior  during  evaporation.  On  the  top  of  the  pan  is 
a  dome  or  short  tower,  from  which  a  pipe  leads  to  a  receptacle,  called 
the  "  catch-all,"  that  retains  any  liquid  which  may  escape  from  the 
pan.  A  small  pipe  returns  this  liquid  to  the  pan,  and  a  larger  one 
connects  the  "  catch-all  "  with  the  vacuum  pump,  which  is  an  ordi- 
nary double-cylinder  air  pump  of  large  size,  driven  by  an  engine. 
An  injector  pump,  which  condenses  the  steam  directly,  may  be  used. 
The  pan  is  generally  heated  by  steam  coils  within  it,  or  by  a  steam 
jacket,  or  by  both. 

A  very  efficient  method  of  vacuum  evaporation  is  that  obtained 
by  the  use  of  Multiple  Effect  Systems.  In  these  greater  economy  of 
fuel  for  heating  is  secured.  The  apparatus  consists  usually  of  two 
or  more  simple  vacuum  pans,  so  joined  together  that  the  steam  from 
the  boiling  liquid  in  the  first  pan  is  made  to  pass  through  the  coils 
and  jacket  of  the  second  pan,  and  the  steam  generated  in  the  second 
pan  goes  through  the  coils  and  jacket  of  the  third,  and  so  on  through 
the  system.  The  vacuum  maintained  in  each  pan  of  the  series  is 
greater  than  in  the  one  preceding.  Hence,  notwithstanding  its 
increased  concentration,  the  boiling  point  of  the  Uquid  in  the  second 
pan  is  so  low,  that  the  steam  from  the  first  pan  is  sufficiently  hot  to 
boil  it.  Similarly  the  steam  from  the  second  pan  is  made  to  boil 
the  liquid  in  the  third,  in  which  there  is  still  less  pressure,  and  so  on 
to  the  last  pan,  in  which  the  highest  vacuum  is  maintained.  As  a 
rule  only  four  pans  are  used,  for  it  is  very  difficult  to  sustain  the 
vacuum  sufficiently  to  work  another  pan  in  the  series.  In  many  plants 
only  three  pans  (triple  effects)  are  used. 

An  effective  modification  of  this  method  is  the  apparatus  known 
as  the  Yaryan  evaporator  (Fig.  4).  It  is  made  in  triple  and  quad- 
ruple effects,  and  each  pan  is  exactly  like  its  neighbors.  It  consists 
of  an  outside  shell  of  iron,  within  which  is  a  system  of  small  tubes 
(A,  A),  joined  together  in  groups  of  five  or  six,  each  group  constitut- 
ing a  section  or  unit.  The  tubes  in  each  unit  are  so  connected  at 
the  ends  as  to  form  one  continuous  coil.  The  liquor  to  be  evaporated 
is  run  through  the  several  coils  thus  constructed  in  each  pan.  The 
tubes  in  the  first  pan  are  heated  by  steam,  introduced  into  the  shell 
directly  from  a  boiler.  As  the  liquid  flows  through  the  tubes,  it  is 
brought  to  boiling,  and  the  steam  generated  mingles  with  it,  convert- 
ing the  whole  mass  into  foam,  which  runs  through  the  coil  and  spurts 
against  a  baffle  plate  in  the  "  separator  "  (B,  B),  which  is  an  enlarged 
chamber  at  the  end  of  the  shell.  The  steam  and  liquid  are  separated, 
the  liquid  falling  to  the  bottom  and  running  off  into  the  receiver  (C), 


INTRODUCTION  7 

to  be  passed  through  the  tubes  of  the  next  pan.  The  steam  rises, 
passing  through  the  steam  dome  and  "catch-all  "  (D),  and  into  the 
shell  of  the  next  "  effect,"  through  the  coils  of  which  the  liquid  is 
passing  under  still  greater  vacuum,  and  so  on  through  the  system. 
The  apparatus  is  very  economical  in  its  use  of  fuel,  and  as  the  liquid 
is  exposed  in  thin  films  to  the  heat,  the  evaporation  is  rapid;  hence 
the  liquid  is  subjected  to  a  high  temperature  for  only  a  short  time. 


FIG.  4. 


The  apparatus  is  nearly  automatic  in  its  action,  and  needs  little  atten- 
tion. It  can  be  stopped  and  started  quickly,  since  it  contains  only 
a  small  quantity  of  liquid  at  one  time,  and  it  occupies  but  little  floor 
space  when  the  several  "  effects  "  are  placed  one  over  the  other. 

The  ordinary  form  of  vacuum  pan  evaporates  about  8j  Ibs.  of 
water  per  pound  of  coal,  but  it  is  said  that  the  best  forms  of  Yaryan 
apparatus  evaporate  from  23 J  to  25  Ibs.  of  water  per  pound  of  coal 
in  a  triple  effect,  and  30J  Ibs.  in  a  quadruple  effect.* 

The  Kestner  evaporator  utilizes  the  "  climbing  film  "  principle, 
by  which  the  liquid  to  be  evaporated  is  automatically  distributed 
over  the  heating  surface,  without  the  use  of  pumps.  The  apparatus 
is  built  in  multiple  effect  and  each  pan  (Fig.  5)  consists  of  a  narrow 
vertical  shell  (M)  containing  a  number  of  small  tubes  (R)  through 
which  the  liquor  passes  upward  from  the  bottom.  The  tubes  are 
tightly  fixed  into  plates  at  top  and  bottom  and  are  entirely  surrounded 
and  heated  by  steam  in  the  shell  (M).  The  tubes  are  about  twenty- 
three  feet  long  and  are  open  at  top  and  bottom.  Liquor  is  fed  in 
through  the  valve  (V)  and  the  supply  so  limited  that  a  relatively 

*  J.  Soc.  Chem.  Ind.,  1895,  112. 


8 


OUTLINES  OF  INDUSTRIAL  CHEMISTRY 


small  quantity  enters  each  tube,   where  it  at  once  begins  to  boil: 

the  vapor  evolved  rushes  up  the  tube,  carrying  some  of  the  liquor 
along  and  distributing  it  in  a  thin  film  on  the 
hot  tube  wall.  Emerging  from  the  top  of  the 
tubes  the  foaming  mixture  of  vapor  and  liquor 
is  discharged  against  the  vanes  of  a  centrifugal 
separator  (D)  by  which  the  concentrated  liquor 
is  whirled  against  the  walls  of  the  enlarged 
vapor  space  (S).  The  liquid  flows  down  the 
walls  and  passes  out  at  (L),  while  the  vapor 
rises  through  (B)  and  passes  to  the  shell  of  the 
next  effect,  or  to  the  condenser.  The  separa- 
tion of  vapor  and  liquor  is  claimed  to  be  so 
complete,  that  practically  no  entrainment  re- 
sults :  only  a  small  quantity  of  liquid  is  in  the 
apparatus  and  the  time  of  heating  is  short; 
only  about  two  minutes  being  required  for  the 
passage  through  the  tubes.  The  drop  in  tem- 
perature between  any  two  pans  of  the  series  is 
small,  ranging  from  8°  to  12°  C.  Thus  four  and 
five  effects  are  often  used  in  series.  The  appa- 
ratus occupies  little  floor  space,  gives  little 
trouble  from  scaling  of  the  tubes,  and  is  easily 
washed  out. 

The  Lillie  evaporator  is  a  very  efficient  type 
of  multiple  effect  (Fig.  6).     Slightly  inclined 

straight  tubes  (A)  tightly  fastened  at 

one  end  in  the  thick  plate  (C)  open 

into  the  steam  space  (B).    The  other 

ends  of  the  tubes  are  closed,  except 

for  a  small  air  vent,  and  are  unsup- 
ported. Thus  they  expand  and  con- 
tract freely,  preventing  strains  and 

resulting  leaks.    In  the  upper  part  of 

the  effect  is   a  row  of  distributing 

pipes  (D),  each  having  a  longitudinal 

slot  on  its  upper  side.     These  pipes 

are   closed   at   one   end ;   the   other 

opens  into  a  distributing   box   (E). 

The  liquor  to  be  evaporated  enters 

through   (G),  passes   into  (D),  and  FIG.  6. 


FIG.  5. 


INTRODUCTION  9 

flowing  from  the  slots  in  thin  films,  is  showered  uniformly  over  the  hot 
tubes  (A),  from  whose  outer  surface  the  evaporation  takes  place.  The 
liquor  drips  from  tube  to  tube,  collecting  in  the  float  box  (F),  from 
which  the  suction  pipe  of  the  centrifugal  pump  (H)  draws  it,  to  again 
pass  over  the  tubes.  The  float  in  the  box  (F)  operates  a  valve  which 
allows  fresh  liquor  to  enter  the  effect  just  fast  enough  to  replace  that 
vaporized  and  what  passes  from  the  discharge  pipe  (J)  as  concentrated 
liquor.  On  (J)  is  a  regulating  valve  governing  the  level  of  the  liquor 
in  (F)  and  thus  controlling  the  rate  of  feed ;  the  slower  the  discharge, 
the  greater  the  concentration.  The  float  completely  closes  the  feed 
valve  when  the  liquor  rises  to  a  definite  height  in  (F) ;  the  discharge 
valve  in  the  last  effect  thus  automatically  controls  the  flow  of  the 
liquor  from  effect  to  effect,  by  influencing  the  action  of  the  feed 
valves.  The  tubes  (A)  are  heated  by  live  or  exhaust  steam,  or  by 
vapor  from  the  preceding  effect,  which  enters  the  steam  chamber  (B) ; 
the  hot  water  condensed  in  (A)  collects  in  the  bottom  of  (B),  and  pass- 
ing the  steam  trap  goes  to  the  steam  space  of  the  next  effect;  thus 
being  under  great  vacuum,  it  gives  up  part  of  its  heat  as  steam,  which 
assists  in  the  heating  of  this  effect.  The  vapor  from  each  effect  also 
enters  the  steam  space  (B)  of  the  next. 

DISTILLATION 

Distillation  is  the  process  of  vaporizing  a  liquid  and  recovering  it 
by  condensing  the  vapors.  The  liquid  formed  by  this  condensation 
is  called  the  distillate.  Distillation  is  chiefly  employed  to  separate 
a  liquid  from  non- volatile  matter  dissolved  or  suspended  in  it ;  or  to 
separate  one  liquid  from  a  mixture  of  liquids  of  different  boiling 
points;  that  one  having  the  lowest  boiling  point  being  the  first  to 
begin  to  pass  off  as  vapor. 

The  separation  of  two  miscible  liquids  by  distillation  depends  on 
the  difference  between  the  composition  of  the  vapor  and  of  the  boil- 
ing liquid  from  which  it  comes ;  *  and  while  never  perfect  is  more 
complete  the  greater  the  difference  in  composition.  Most  liquid 
mixtures  evolve  a  vapor  containing  more  of  the  low-boiling  constituent 
than  does  the  liquid  itself;  but  in  some  cases  the  reverse  is  true  be- 
tween certain  limits  of  composition,  and  such  liquids  always  give 

*  The  vapor  pressures  of  the  pure  liquids,  or  what  is  practically  the  same  thing, 
their  boiling  points,  are  not  the  essential  factors ;  thus  both  glycerine  and  water, 
and  hydrochloric  acid  and  water,  differ  widely  in  vapor  pressures  and  boiling  points, 
but  glycerine  and  water  are  easily  separated  by  distillation  while  the  separation  of 
hydrochloric  acid  and  water  by  this  means  is  impossible. 


10  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

mixtures  of  maximum  or  minimum  boiling  point,  which  cannot  be 
separated  by  distillation  as  the  vapor  and  liquid  compositions  are  in 
these  cases  the  same.* 

During  a  distillation  the  boiling  point  gradually  rises,  and  at  the 
end  there  remains  in  the  still  a  relatively  small  amount  of  the  high- 
boiling  liquid  very  free  from  the  other  component,  or  else  a  mixture 
of  maximum  boiling  point.  While  the  distillate  has  been  enriched 
in  the  low-boiling  constituent,  it  is  far  from  pure,  but  repetition  of 
the  distillation  improves  the  separation.  In  general  it  is  easier  to 
secure  the  high-boiling  liquid  free  from  the  other  than  the  reverse. 

If  a  mixed  vapor  be  slowly  cooled,  the  liquid  to  condense  is  that  in 
equilibrium  with  the  vapor;  thus  it  is  largely  the  less  volatile  com- 
ponent which  separates  first.  By  abstracting  only  enough  heat  to 
condense  a  part  of  the  vapor,  the  remainder  is  greatly  enriched  in  the 
volatile  constituent ;  this  fractional  condensation  is  attained  by  using 
a  condenser  with  relatively  hot  cooling  medium,  the  uncondensed 
vapors  passing  to  a  cold  condenser  for  complete  condensation.  From 
the  fractional  or  partial  condenser,  the  condensate  returns  to  the  still 
for  reboiling,  to  remove  the  remainder  of  the  volatile  component. 
Fractional  condensation  is  equivalent  to  a  redistillation,  without  the 
consumption  of  additional  heat. 

The  chief  parts  of  every  distilling  apparatus  are  the  boiler  or  still 
and  the  condenser.  The  still  is  usually  iron  or  copper,  and  may  be 
heated  directly  by  a  furnace,  or  by  a  steam-jacket,  or  a  coil.  The 
condenser  is  a  coil  of  pipe,  or  a  system  of  tubes,  or  a  double-walled 
chamber,  submerged  in  a  tank  of  cold  water.  Condensers  are  usually 
made  of  iron  or  copper,  but  lead,  silver,  earthenware,  or  glass  tubes 
are  sometimes  used.  The  fractional  condensation  apparatus  is 
placed  between  the  still  and  the  final  condenser ;  it  may  consist  of  a 
series  of  chambers,  or  of  pipes  or  U-tubes,  surrounded  by  a  water- 
bath  or  other  liquid  at  a  temperature  between  the  boiling  points  of 
the  liquids  to  be  distilled. 

The  condensate  from  a  fractional  condenser  is  richer  in  the  volatile 
component  than  is  the  liquid  in  the  still ;  it  is,  therefore,  not  in  equi- 
librium with  the  vapor  from  the  still,  and  if  brought  into  contact 

*  Thus  water  and  alcohol  have  a  mixture  of  minimum  boiling  point  at  96 
per  cent  alcohol,  a  mixture  more  volatile  than  either  component ;  water  and 
hydrochloric  acid  containing  28  per  cent  hydrochloric  acid  have  a  maximum  boiling 
point ;  mixtures  containing  more  acid  than  this  evolve  vapors  richer  in  hydrochloric 
acid  ;  if  less  than  28  per  cent  acid  is  present,  more  water  in  proportion  is  given  off ; 
in  either  case  there  is  finally  left  in  the  still  this  constant  boiling  mixture  which 
cannot  be  separated  by  further  boiling. 


INTRODUCTION  11 

with  that  vapor,  an  interchange  of  heat  results,  accompanied  by  a 
volatilization  of  the  low-boiling  constituent  and  a  condensation  of  the 
high-boiling  one,  which  further  enriches  the  vapor  and  improves  the 
separation,  without  any  additional  expenditure  of  heat.  This  process 
is  called  dephlegmation,  and  to  secure  the  maximum  efficiency,  must 
be  repeated  a  number  of  times.  The  mixed  vapors  from  the  still 
are  bubbled  through  a  series  of  shallow  layers  of  liquid,  through  which 
passes  in  counter-current  flow,  the  partial  condensate  from  the  frac- 
tional condenser;  this  condensate,  with  its  low-boiling  constituent 
removed  as  completely  as  possible,  finally  flows  back  into  the  still. 
The  apparatus  for  this,  called  the  dephlegmator,  or  "  column,"  usually 
consists  of  a  tall  tower  (Fig.  8,  B,  B)  set  above  the  still,  and  divided 
by  a  number  of  perforated  horizontal  plates  into  many  shallow  cham- 
bers, through  each  of  which  the  returning  liquid  must  flow  on  its 
way  to  the  still.  The  vapors  from  the  still  pass  up  through  the  open- 
ings in  the  plates,  bubbling  through  the  shallow  layers  of  the  liquid 
and  give  up  heat  to  it,  causing  vaporization  of  its  volatile  constituents. 
The  boiling  of  the  liquid  in  all  of  the  chambers  is  done  by  the  heat 
in  the  vapors  entering  the  lowest  chamber :  any  condensation  in  the 
tower  results  in  greater  coal  consumption  to  restore  the  heat  thus 
lost.  The  chief  object  of  the  dephlegmator  is  to  boil  the  liquid  in 
the  several  chambers,  and  deliver  the  enriched  mixed  vapors  to  the 
fractional  condenser.  As  radiation  from  the  walls  of  the  column 
causes  condensation  and  loss  of  heat,  the  column  should  be  covered 
or  lagged. 

In  an  ordinary  distillation,  even  with  use  of  fractional  condenser 
and  dephlegmating  column,  it  is  only  at  the  end  of  the  operation  that 
there  remains  in  the  still  the  high-boiling  component  in  a  practically 
pure  state ;  at  any  earlier  stage  in  the  process,  however,  it  is  possible 
to  dephlegmate  the  low-boiling  component  from  the  liquid  in  the  still, 
by  using  a  dephlegmating  column  below  the  still.  This  is  done  in 
practice  by  admitting  the  liquid  mixture  to  be  distilled  into  the  middle 
of  a  long  column,  the  overflow  from  which  passes  down  to  the  still 
in  which  there  is  only  pure  high-boiling  liquid;  the  rising  vapors 
carry  the  low-boiling  constituent.  The  original  mixture  can  now  be 
admitted  and  the  distillate  and  high-boiling  residue  withdrawn 
continuously  from  the  apparatus.  Also,  the  column,  below  the  point 
of  admission  of  the  liquid  to  be  distilled,  accomplishes  the  redistil- 
lation of  the  overflow  from  the  apparatus  above,  without  further 
consumption  of  heat;  in  addition  to  the  great  advantage  of  continuity 
of  operation,  this  type  of  column  gives  the  best  heat  economy  of  any 


12 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


method  of  distillation,  and  is  generally  employed  except  where  special 
conditions  render  it  inadvisable.  The  heat  economy  can  be  still 
further  improved  if  the  feed  liquor  be  heated  by  using  it  as  cooling 
medium  in  the  fractional  or  final  condensers. 

In  Coupler's  still  (Fig.  7)  a  tower  (A)  is  placed  on  top  of  the  boiler 
(B) ;  between  the  tower  and  the  condenser  is  a  series  of  chambers 
(C,  C)  surrounded  by  a  water  bath,  which  may  be  kept  at  any 

desired  temperature.  While 
the  mixed  vapors  are  passing 
through  the  chambers,  the 
high-boiling  constituents  are 
condensed,  and  the  vapor 
of  the  more  volatile  liquid 
passes  through  (E)  to  the 
condenser  (F).  A  pipe  (D) 
returns  the  condensed  heavy 
liquid  to  the  tower,  to  be 
redistilled  or  dephlegmated. 
The  French  column  ap- 
paratus (Fig.  8)  has  a  series  of  U-tubes  (C)  surrounded  by  a  water  bath. 
The  column  or  dephlegmator  (B)  is  divided  into  chambers  by  plates, 
each  of  which  has  a  central  opening  covered  by  a  dome ;  a  small  over- 
flow pipe  passes  from  each  plate  to  the 
next.  The  vapors  from  the  boiler  (A) 
pass  up  through  the  central  openings 
and  bubble  out  under  the  edges  of  the 
domes  through  the  layer  of  liquid  on 
each  plate.  The  liquid  thus  condensed 
flows  down  through  the  overflow  pipes, 
and  returns  to  the  boiler. 

The  Coffey  still  (Fig.  9)  is  much 
used  for  alcohol  and  gas  liquor  dis- 
tillation. This  consists  of  two  towers, 
one,  called  the  "analyzer"  (E),  re- 
ceiving free  steam  from  the  boiler, 
and  "the  other,  called  the  "rectifier" 
(G),  containing  a  long  coil  of  pipe 
(C,  C),  through  which  the  liquid  to  be 
distilled  flows  on  its  way  to  the  ana- 
lyzer. The  analyzer  is  divided  into  a  series  of  chambers  by  horizontal, 
perforated  plates  (A) ;  from  each  plate  an  overflow  pipe  (F)  passes 


FIG.  8. 


INTRODUCTION 


13 


down  and  dips  into  a  shallow  cup  (H)  on  the  next  plate  below  and 
holding  liquid  enough  to  form  a  hydraulic  seal  at  the  lower  end  of 
each  overflow  pipe.  These  pipes  project  about  an  inch  or  so  above 
the  plate  in  which  they  are  set,  thus  determining  the  depth  of  the 
liquid  layer  on  each  plate.  The  rectifier  is  divided  into  chambers 
by  perforated  plates,  but  has  overflow  pipes  in  its  lower  half  only. 
In  the  chambers  lie  the  coils  of  pipe  (C)  through  which  the  liquid  to 
be  distilled  passes  on  its  way  to  the  analyzer.  This  still  works  as 


FIG.  9. 

follows :  Steam  from  the  boiler  is  blown  through  (K)  into  the  ana- 
lyzer, and  passes  from  the  top  of  the  analyzer  through  the  pipe  (L) 
to  the  rectifier.  The  liquid  to  be  distilled  is  pumped  through  the 
pipe  (B)  and  the  coil  (C)  in  the  rectifier,  and  is  delivered  at  the  top 
of  the  analyzer  through  the  pipe  (D).  The  cold  liquid  is  heated 
by  the  steam  surrounding  the  coils,  and  is  delivered  hot  into  the 
analyzer. 

Since  steam  is  being  forced  up  through  the  perforations,  the  liquid 
cannot  pass  down  through  them,  but  is  forced  to  spread  out  over 
the  plate,  and  run  down  the  overflow  pipe  (F)  to  the  next  plate,  and 
so  through  the  analyzer.  The  steam,  bubbling  up  through  the  thin 
layers  of  liquid,  heats  it  very  hot,  and  causes  the  volatile  substances 
to  distil  off  with  the  steam.  This  mixture  of  steam  and  volatile 
matter  passes  from  the  top  of  the  analyzer,  through  (L),  to  the  bot- 
tom of  the  rectifier.  During  its  passage  up  the  rectifier,  the  steam 
is  condensed  by  coming  into  contact  with  the  cold  pipes  (C,  C), 


14       .         OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

through  which  the  liquid  is  flowing  to  the  analyzer.  Thus  only  the 
more  volatile  matters  pass  out  at  the  top  of  the  rectifier,  and  go  to 
the  condenser  (O).  The  water  condensed  in  the  rectifier  contains 
some  volatile  matter,  so  it  is  pumped  to  the  top  of  the  analyzer  and 
mixes  with  the  fresh  liquor  to  be  distilled.  From  the  bottom  of  the 
analyzer  a  waste  pipe  (J)  carries  off  the  spent  liquor  which  has  been 
deprived  of  its  volatile  matter.  The  rectifier  (G)  is  a  combination 
of  fractional  condenser  and  dephlegmator ;  the  analyzer  (E)  is  strictly 
a  dephlegmating  column. 

Distillation  with  use  of  a  dephlegmating  column  is  sometimes 
called  rectification,  but  this  term  should  be  reserved  for  such  an  oper- 
ation conducted  so  as  to  eliminate  one  or  more  undesirable  constit- 
uents. (See  Alcohol,  p.  459.) 

Distillation  in  vacuum  is  sometimes  employed,  and  will  be  de- 
scribed in  connection  with  the  industries  in  which  it  is  used. 

SUBLIMATION 

Sublimation  is  the  process  of  vaporizing  a  solid  substance  and  condensing 
the  vapors  to  again  form  the  solid  directly,  without  passing  through  an  intermediate 
liquid  state.  There  are  very  few  substances  which  vaporize  without  melting,  but 
in  all  cases  of  sublimation,  the  change  from  the  vapor  to  the  solid  state  is  direct, 
and  without  any  formation  of  liquid.  The  sublimed  body  is  recovered  unchanged 
chemically,  but  its  physical  properties  are  often  more  or  less  altered.  In  most  cases, 
the  temperature  does  not  exceed  a  low  red  heat.  Dissociation  often  occurs  in  the 
process. 

FILTRATION 

Filtration  is  the  process  of  separating  suspended  solid  matter 
from  a  liquid,  by  causing  the  latter  to  pass  through  the  pores  of 
some  substance,  called  a  filter.  The  liquid  which  has  passed  through 
the  filter  is  called  the  filtrate.  The  filter  may  be  paper,  cloth,  cotton- 
wool, asbestos,  slag-  or  glass-wool,  unglazed  earthenware,  sand,  or 
other  porous  material. 

Filtration  is  very  frequently  employed  in  chemical  technology, 
and  it  often  presents  great  difficulties.  In  most  technical  opera- 
tions, cotton  cloth  is  the  filtering  material,  but  occasionally  woollen 
or  hair  cloth  is  necessary.  The  cloth  may  be  fastened  on  a  wooden 
frame  in  such  a  way  that  a  shallow  bag  is  formed,  into  which  the 
turbid  liquid  is  poured.  The  filtrate,  in  this  case,  is  cloudy  at  first, 
but  soon  becomes  clear,  and  then  the  turbid  portion  is  returned  to 
the  filter.  Filtration  is  often  retarded  by  the  presence  of  fine,  slimy 
precipitates,  or  by  the  formation  of  crystals  in  the  interstices  of 
the  cloth,  from  the  hot  solution.  Any  attempt  to  hasten  filtration, 


INTRODUCTION  15 

by  scraping  or  stirring  the  precipitate  on  the  cloth,  will  always  cause 
the  filtrate  to  run  turbid. 

A  better  form  is  the  "  bag-filter,"  which  is  a  long,  narrow  bag  of 
twilled  cotton,  supported  by  an  outside  cover  of  coarse,  strong  netting, 
capable  of  sustaining  a  considerable  weight  and  hydrostatic  pressurec 
These  bags  are  often  five  or  six  feet  long,  and  eight  inches  or  more  in 
diameter.  The  open  end  of  the  bag  is  tied  tightly  around  a  metallic 
ring  or  a  nipple,  by  which  the  whole  is  suspended,  and  through  which 
the  liquor  to  be  filtered  is  introduced.  When  hot  liquids  are  filtered, 
the  bags  are  often  hung  in  steam-heated  rooms,  the  temperature 
being  nearly  that  of  the  liquid. 

In  pressure  filtration,  the  liquid  is  forced  through  the  interstices 
of  the  filter  by  direct  atmospheric  pressure,  the  air  being  exhausted 


FIG.  10. 

from  the  receiver;  or  by  hydrostatic  pressure,  obtained  either  by 
means  of  a  high  column  of  the  liquid,  or  by  a  force  pump:  By  the 
first  method,  called  suction  filtration,  the  liquid  may  be  forced  down- 
ward through  the  filter  into  a  receiver;  the  precipitate  collects  on 
the  top  of  the  filter  and  becomes  a  part  of  the  filtering  layer.  This 
sometimes  causes  difficulty,  for  the  particles  of  certain  precipitates 
unite  to  form  an  impervious  layer.  Or  the  filtrate  may  be  drawn 
upicard  through  the  filter,  which  is  suspended  in  the  liquid  to  be 
filtered ;  thus  clogging  does  not  occur  so  easily,  as  a  large  part  of  the 
precipitate  settles  to  the  bottom  of  the  vessel  and  does  not  come  in 
contact  with  the  filter  until  most  of  the  liquid  has  been  drawn  off. 

In  technical  work,  pressure  is  usually  obtained  by  the  filter  press 
(Figs.  10  and  11).  This  is  a  strong  iron  frame,  in  which  a  number 
of  cells  of  iron  or  other  metal  are  supported  and  tightly  clamped  by 


16 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


FIG.  11. 


the  screw  (H).  Each  cell  is  made  up  of  two  flat  metal  plates  (A), 
with  planed  edges,  which  are  separated  by  a  hollow  "  distance  frame  " 
(B).  Between  the  filter  plates  (A)  and  the  "distance  frames"  (B) 
are  stretched  the  filter  cloths  (C),  which  are  held  in  place  by  the 
clamping  of  the  edges  of  the  plates  and  frames.  The  face  of  each 

plate  is  channelled  by  grooves 
leading  to  an  outlet  (D)  at  the 
lower  edge  of  the  plate.  In  a 
corner,  or  at  one  side  of  each  plate, 
distance  frame,  and  filter  cloth  is 
a  hole  (E)  in  such  a  position  that 
when  clamped  in  the  press  the 
holes  form  a  continuous  channel 
(E,  E,  E)  through  the  series  of  cells. 
This  forms  the  feed  channel 
through  which  the  material  to  be 
filtered  enters  the  cells;  a  side 
opening  from  this  channel  in  each 
distance  frame  admits  the  material 
to  the  space  between  the  plates. 
The  liquid  passes  through  the  filter  cloth  (C)  into  the  grooves  leading 
to  the  outlet  (D)  and  escapes  through  the  cocks  (F),  while  the  sediment 
retained  by  the  cloth  accumulates  in  the  distance  frames,  forming  a 
solid  cake,  which  finally  fills  each  cell  completely. 

A  powerful  pump  supplies  a  continuous  stream  of  the  liquid  and 
forces  the  sediment  into  the  cells,  where  it  collects  in  a  cake  and 
offers  increasing  resistance  to  the  passage  of  the  liquid.  The  limit 
of  pressure  employed  to  force  the  liquid  through  depends  on  several 
factors,  and  is  usually  determined  by  experiment  for  each  material 
to  be  filtered.  When  this  pressure  limit  is  reached,  the  process  is 
stopped,  the  cell  taken  apart,  and  the  cake  of  sediment  removed; 
then  the  cells  are  returned  to  the  press  frame,  clamped  in  position, 
and  the  operation  repeated.  The  air  chamber  (G)  equalizes  the  pres- 
sure during  the  working  of  the  pump. 

Another  type  of  press  is  the  central  feed  machine  in  which  the 
feed  channel  (E,  E)  passes  through  the  middle  of  each  plate  (see  Fig.  10). 
In  each  filter  cloth,  to  correspond  with  this  opening,  there  is  a  hole, 
around  which  a  small  clamping  ring  makes  a  tight  joint. 

The  number  of  cells  in  a  single  press  may  range  from  half  a  dozen 
to  a  couple  of  hundred,  according  to  the  amount  of  material  to  be 
filtered.  The  average  sizes  of  frame  are  from  18  to  36  inches  in  di- 


INTRODUCTION 


17 


ameter,  and  the  width  of  the  frames,  which  determines  the  thickness 
of  the  cake,  may  be  J  inch  to  3  inches.  The  proper  size  and  thickness 
of  cake  must  be  determined  by  experiment  for  each  material.  Very 
often  the  filter  press  is  fitted  with  special  arrangements  for  washing  the 
cake  to  remove  the  soluble  matter.  This  is  usually  accomplished  by  a 


LOCK    NUT 
ADJUSTING    NL 


FIG.  126. 


special  feed  channel  from 
which  the  wash-water  is  forced 
through  the  cakes  as  they  rest 
in  the  cells.  Sometimes  the 
cells  are  surrounded  with 
jackets  for  steam  heating,  or 
refrigeration,  for  filtration  at 
high  or  low  temperatures. 

The  leaf  filter  consists  of 
a  closed  chamber  containing 
numerous  filter  leaves,  made 
of  thin  wood  slats  or  metallic 
wire  webbing,  covered  on  both 
sides  by  the  filter  cloth;  the  cloth  is  stitched  or  clamped  around 
the  edges  of  the  leaf.  A  nipple  at  the  top  or  side  of  the  leaf,  con- 
necting with  its  interior,  serves  as  the  means  of  suspending  the  leaf 
in  the  chamber,  and  also  as  exit  for  the  filtrate,  which  passes  into  the 
filtrate  conduit.  A  shut-off  valve  is  placed  between  the  nipple  and 
the  conduit. 

In  Fig.  12  *  is  shown  a  leaf  filter  of  the  "  clam  shell  "  type,  in 
which  the  chamber  consists  of  two  semi-cylindrical  castings,  the 
upper  one  fixed  in  suitable  supports,  ahd  the  lower  one  so  hinged  that 
it  can  swing  away  from  the  top  half,  permitting  the  dumping  of  all 
the  cakes  at  once,  without  disturbing  the  filter  leaves.  A  rubber 

*  Jour.  Ind.  Eng.  Chem.,  1914,  (VI)  143. 
c 


18 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


gasket  renders  the  joint  tight  when  the  filter  is  closed.  A  short  glass 
tube  between  the  outlet  nipple  and  the  filtrate  conduit  makes  it 
possible  to  detect  a  broken  filter  cloth  by  the  turbidity  of  the  liquid 
passing. 

The  chamber  is  filled  under  pressure  with  the  liquid  to  be  filtered 
and  the  leaves  are  thus  entirely  submerged ;  the  liquid  passes  through 
the  cloth  into  the  interior  spaces  of  the  filter  leaf,  and  thence  out  by 
the  nipple  to  the  filtrate  conduit.  The  solid  matter  is  retained  on  the 
cloth  and  coats  both  sides  of  the  leaves,  forming  cakes  of  uniform 
thickness  on  each.  When  the  cakes  are  sufficiently  thick,  the  feed 
is  stopped  and  the  cakes  washed  without  disturbing  them,  by  intro- 
ducing water  through  the  sludge  inlet,  or  by  a  special  manifold  pipe 
delivering  into  the  spaces  between  the  cakes.  After  the  washing,  the 
residual  liquor  is  drained  out  of  the  chamber,  and  the  cakes  freed 
from  most  of  the  retained  liquor  by  compressed  air  admitted  to  the 
chamber.  The  cakes  are  then  loosened  from  the  cloths  by  introducing 

compressed  air,  steam,  or  water 
through  the  filtrate  outlet ;  this 
passes  into  the  space  inside  the 
leaf  frames,  and  escapes  through 
the  cloths,  forcing  the  cakes  from 
the  filtering  surfaces. 

Another  type  of  leaf  filter 
has  the  frames  suspended  longi- 
tudinally in  the  chamber,  and 
the  outlets  for  the  filtrate  pass 
through  the  press  head.  The 
press  head  and  frame  carrying 
the  filter  leaves  are  supported 
on  a  carriage,  by  which  they  can 
be  moved  out  of  the  chamber 
for  discharge  of  the  cakes.  This 
press  is  set  at  an  incline  of  8° 
to  9°,  to  facilitate  movement 
of  the  carriage  when  the  leaves 
are  all  covered  with  cakes. 
The  centrifugal  machine  (Fig.  13)  is  much  used  to  separate  liquid 
from  solid  matter.  It  works  rapidly  and  leaves  the  substance  almost 
dry.  It  is  a  cylindrical  cage  or  basket  (A)  of  wire  gauze  or  perforated 
sheet  metal,  fixed  on  a  vertical  shaft  (B)  which  rotates  at  very  high 
speed.  The  contents  of  the  cage  are  thrown  against  the  perforated 


FIG.  13. 


INTRODUCTION  19 

wall  by  the  centrifugal  force,  the  solid  matter  being  held  by  the  screen ; 
the  liquid  passing  through  impinges  upon  the  fixed  casing  (C)  sur- 
rounding the  rotating  cage.  These  machines  vary  in  size  from  12  to 
60  inches  diameter,  and  8  to  30  inches  depth  of  basket.  Two  forms 
are  in  use:  the  over-driven  type,  in  which  the  driving  pulley  (P) 
is  fixed  at  the  upper  end  of  the  shaft,  above  the  basket ;  and  the  under- 
driven  type,  in  which  the  cage  is  placed  on  the  upper  end  of  the 
shaft,  and  the  pulley  below.  In  the  over-driven  type,  the  shaft  is 
usually  hung  in  flexible  bearings,  so  the  cage  may  adjust  itself  to  any 
change  of  the  centre  of  gravity,  caused  by  unequal  loading,  and  runs 
without  vibration. 

Sand  filters  are  sometimes  used  for  work  on  a  large  scale.  These 
are  made  as  follows :  Into  a  box  having  a  perforated  bottom  is  put  a 
layer  of  coarse  gravel ;  this  is  covered  with  finer  pebbles ;  these  by 
sand,  and  a  jute  or  canvas  cloth  covers  the  whole.  A  wooden  or  iron 
grating  is  added  to  protect  the  filter  when  the  sediment  is  shovelled 
out.  The  filter  is  often  placed  over  a  receptacle  from  which  the  air 
may  be  exhausted,  thus  affording  pressure  filtration  if  necessary. 


CRYSTALLIZATION 

Crystals  are  chemically  homogeneous  bodies,  usually  having 
regular  polyhedral  forms,  and  whose  molecules  have  arranged  them- 
selves regularly  according  to  definite  laws.  The  tendency  to  form 
crystals  is  common  to  almost  all  chemical  compounds  under  certain 
conditions,  the  forms  of  the  crystals  being  characteristic  of  the  sub- 
stance. 

Crystals  may  form  from  a  fusion,  or  by  sublimation;  but  crys- 
tallization almost  always  takes  place  from  solution. 

In  general,  the  solubility  of  a  substance  increases  as  the  tempera- 
ture of  the  liquid  rises;  when  the  boiling  point  is  reached,  under 
atmospheric  pressure,  the  rise  in  temperature  ceases,  and  no  more  of 
the  substance  dissolves.  When  a  liquid  has  dissolved  all  of  a  solid 
that  it  can  hold  in  solution  at  a  certain  temperature  and  pressure,  it 
is  said  to  be  saturated  for  that  temperature.  Any  decrease  in  the 
temperature  results  in  the  separation  of  a  part  of  the  substance 
usually  as  crystals.  There  are  a  few  instances  where  the  maximum 
solubility  is  reached  at  temperatures  much  below  the  boiling  point 
of  the  solution,  the  most  notable  of  these  salts  being  sodium  car- 
bonate and  sodium  sulphate,  both  reaching  the  maximum  solubility 
below  35°  C,  During  the  formation  of  the  crystal,  there  is  a  ten- 


20  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

dency  to  exclude  from  it  all  matter  not  homogeneous  with  it ;  hence 
this  is  an  excellent  method  of  purifying  salts.  But  if  a  concentrated 
solution,  which  is  very  impure,  is  allowed  to  crystallize,  the  impuri- 
ties may  become  enclosed  in  or  entangled  among  the  crystals  as 
they  form,  producing  an  impure  product.  This  can  often  be  pre- 
vented by  stirring  the  solution  while  crystallizing,  thus  causing  the 
formation  of  very  fine  crystals  or  "  crystal  meal,"  which  may  be 
more  readily  washed  free  from  mother-liquor  and  impurities.  The 
liquid  from  which  the  crystals  have  deposited,  is  called  the  mother- 
liquor;  it  contains  the  greater  part  of  the  soluble  impurities  present 
in  the  original  solution,  and  also  a  considerable  quantity  of  the  salt, 
which  has  not  deposited  as  crystals.  The  amount  of  the  latter 
depends  upon  the  temperature  at  which  the  crystallization  took 
place.  By  further  evaporation  more  crystals  may  be  obtained,  but 
they  are  less  pure  than  those  first  separated.  Thus  the  impurities 
accumulate  in  the  mother-liquor,  and  in  many  cases,  being  valuable 
salts  themselves,  are  recovered,  and  add  to  the  profits  of  the  indus- 
try. On  the  other  hand,  the  mother-liquors  from  some  processes 
are  the  cause  of  much  annoyance  and  expense  to  the  manufacturer, 
since  from  their  corrosive,  poisonous,  or  offensive  nature,  they  can- 
not be  run  into  the  streams  or"  sewers,  and  their  disposal  in  some 
other  way  becomes  necessary. 

If  a  concentrated  solution  is  allowed  to  stand  quietly  while  crys- 
tallizing, especially  if  there  is  a  considerable  quantity  of  the  liquid 
and  the  temperature  falls  very  slowly,  the  crystals  formed  are  usually 
large  and  well  defined ;  on  the  other  hand,  if  it  be  stirred,  the  crystals 
are  small  and  imperfectly  developed,  constituting  the  crystal  meal 
above  mentioned.  Since  large  crystals  are  compact  and  offer  a 
relatively  small  surface  to  the  action  of  water,  they  dissolve  very 
slowly,  unless  pulverized.  Crystal  meal  dissolves  more  readily,  and 
for  this  reason  is  becoming  more  and  more  popular  with  manu- 
facturers. 

CALCINATION 

Calcination  is  the  process  of  subjecting  a  substance  to  the  action 
of  heat,  but  without  fusion,  for  the  purpose  of  causing  some  change 
in  its  physical  or  chemical  constitution.  The  objects  of  calcination 
are  usually :  (1)  to  drive  off  water,  present  as  absorbed  moisture, 
as  "  water  of  crystallization,"  or  as  "  water  of  constitution  " ;  (2)  to 
drive  off  carbon  dioxide,  sulphur  dioxide,  or  other  volatile  constit- 
uent ;  (3)  to  oxidize  a  part  or  the  whole  of  the  substance.  There 
are  a  few  other  purposes  for  which  calcination  is  employed  in  spe- 


INTRODUCTION 


21 


cial  cases,  and  these  will  be  mentioned  in  their  proper  places. 
The  process  is  often  called  "  roasting,  "  firing,"  or  "  burning,"  by 
the  workmen.  It  is  carried  on  in  furnaces,  retorts,  or  kilns,  and 
the  material  is  often  raked  over  or  stirred,  during  the  process,  to 
secure  uniformity  in  the  product. 

The  furnaces  used  for  calcining  substances  vary  much  in  their 
construction,  but  there  are  three  general  classes:  reverberatory, 
muffle,  and  shaft  furnaces  or  kilns. 


FIG.  14. 


Reverberatory  furnaces  are  built  in  many  forms,  but  in  all  cases 
the  flames  and  hot  gases  from  the  fire  come  in  direct  contact  with 
the  material  to  be  calcined,  but  the  fuel  is  separated  from  it.  The 
simplest  and  most  common  form  is  shown  in  Fig.  14.  The  fire 
burns  on  the  grate  at  (G),  and  the  flames,  passing  over  the  bridge  at 
(E),  are  deflected  downward  by  the  low  sloping  roof  of  the  furnace, 
and  pass  directly  over  the  surface  of  the  charge  in  the  bed  of  the 
furnace  at  (B),  finally  escaping  through  the  throat  (F)  into  the  chim- 
ney. The  charge  is  spread  out  in  a  thin  layer  on  the  bed  (B),  and 
may  be  either  oxidized  or  reduced,  according  to  the  method  of  firing 
and  the  amount  of  air  admitted. 

The  revolving  furnace  (Figs.  3  and  47)  is  a  very  important  modi- 
fication of  the  reverberatory  furnace.  This  consists  of  a  horizontal 
or  slightly  inclined  cylinder  (B)  of  iron  or  steel  plates,  lined  with 
fire-brick  or  other  suitable  fire-resisting  material,  and  open  at  each 
end.  The  flames  from  a  grate  (A)  at  one  end  pass  through  it  on  their 
way  to  the  chimney  (D).  The  cylinder  is  revolved  about  its  longi- 
tudinal axis  by  means  of  a  gear.  It  is  turned  until  a  manhole  in 
the  side  is  brought  directly  under  a  hole  in  the  floor  above,  the  bolted 
cover  is  removed,  and  the  charge  dumped  in.  The  revolution  of  the 
cylinder  stirs  the  charge  thoroughly,  and  brings  it  into  intimate  con- 


22 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


tact  with  the  flame.  To  discharge  the  contents,  the  manhole  cover 
is  removed,  the  cylinder  is  rotated,  and  the  material  drops  out  upon 
the  floor  or  into  a  car  placed  for  it.  To  facilitate  discharging,  the 
lining  usually  slopes  from  all  sides  towards  the  manhole.  The  speed 
varies  from  about  two  revolutions  a  minute  to  one  revolution  in 
five  or  ten  minutes.  These  furnaces  are  extensively  used,  their  ad- 
vantages being  the  intimate  mixing  and  even  heating  of  the  charge, 
and  the  large  quantities,  amounting  often  to  several  tons,  which  can 
be  worked  at  one  time. 


'     G 
t  r- 

F 

I 

|  A 

^^ 

P 

^  (^aaa^a^SSSSE 

ggS^^Ss^i 

FIQ.  15. 


Muffle  furnaces  (Fig.  15)  are  so  constructed  that  neither  the  fuel 
nor  the  fire  gases  come  in  direct  contact  with  the  material  to  be  cal- 
cined. A  retort  (A)  of  iron,  brickwork,  or  fire-clay  is  placed  over 
the  fire  grate  (G).  Flues  (F,  F)  are  built  around  the  retort,  and 
through  these  the  hot  gases  from  the  fire  pass  on  their  way  to  the 
chimney  (E). 

Shaft  furnaces  and  kilns  are  of  two  general  classes,  periodic  and 
continuous.  After  a  charge  has  been  calcined,  the  periodic  furnace 
(p.  175)  or  kiln  is  allowed  to  cool  before  it  is  emptied  and  recharged. 
In  the  continuous  variety  (p.  176)  this  is  not  necessary,  and  the  cal- 
cined substance  is  withdrawn  and  fresh  material  added  without  loss 
of  time  or  waste  of  heat.  The  furnaces  may  be  charged  with  alter- 
nate layers  of  fuel  and  material  to  be  calcined.  By  this  method, 
known  as  "  burning  with  short  flame,"  the  material  to  be  calcined  is 
in  close  contact  with  the  fuel,  and  is  of  course  more  or  less  contami- 
nated with  ashes.  In  other  forms  of  shaft  furnaces  (Fig.  74)  the 
fuel  is  burned  on  a  separate  grate,  and  only  the  flames  and  hot  gases 
pass  into  the  shaft;  consequently,  no  ashes  are  left  in  the  product. 
This  process  is  called  "burning  with  long  flame." 

Any  of  the  various  forms  of  furnace  here  mentioned  may  be 
heated  by  natural  gas,  generator  gas,  or  oil.  This  is  very  advanta- 
geous in  the  matter  of  cleanliness  and  of  regularity  of  temperature. 
(See  Fuels.) 


INTRODUCTION  23 


REFRIGERATION 

Since  refrigerating  machines  have  made  artificial  cooling  of  rooms 
and  of  material  possible,  industries  which  were  formerly  only  carried 
on  in  cold  weather  are  now  operated  at  all  seasons.  The  manufacture 
of  ice  is  also  a  large  and  increasing  industry,  and  is  apparently  forcing 
the  natural  product  from  the  market  more  and  more  each  year. 

The  principle  involved  in  a  refrigerating  machine  is  the  rapid 
absorption  of  heat  by  the  rapid  evaporation  of  a  volatile  liquid. 
The  substances  most  used  are  liquefied  ammonia,  sulphur  dioxide, 
carbon  dioxide,  and  the  very  volatile  liquids  derived  from  petroleum, 
chiefly  cymogene  and  rhigolene.  In  this  country  by  far  the  greatest 
number  of  machines  employ  liquid  ammonia. 

The  gas  is  heavily  compressed  and  then  liquefied  by  passing  it 
into  a  coil  over  which  a  large  amount  of  cold  water  flows ;  the  liquid 
is  then  forced  through  a  small  opening  into  a  large  chamber  or  coil 
of  pipe,  from  which  the  gas  formed  may  be  rapidly  exhausted  by  a 
pump.  The  rapid  expansion  and  conversion  of  the  liquid  to  a  vapor 
here  absorbs  much  heat  from  the  walls  of  the  coil  or  chamber,  whose 
temperature  consequently  falls  considerably  below  the  freezing  point 
of  pure  water.  In  order  to  increase  the  external  surface  of  the  expan- 
sion coils,  cast-iron  disks  are  placed  at  frequent  intervals  on  the  pipe 
perpendicular  to  its  line  of  direction.  Only  a  comparatively  small 
amount  of  ammonia  or  other  volatile  liquid  is  necessary  for  the  con- 
tinuous working  of  the  machine.  Since  the  gas  is  returned  to  the 
compressor,  it  is  only  necessary  to  supply  that  lost  by  leakage. 

It  is  often  customary  to  surround  the  expansion  coils  with  a  brine 
or  calcium  chloride  solution,  which  is  then  pumped  through  coils 
or  pipes  in  rooms  to  be  cooled.  For  making  ice,  galvanized  iron 
boxes  are  filled  with  water  and  immersed  in  the  cold  brine. 

In  the  system  shown  in  the  diagram  (Fig.  16)  a  certain  amount 
of  oil  is  injected  into  the  compressor  along  with  each  charge  of  am- 
monia. This  insures  complete  emptying  of  the  compressor  at  each 
stroke,  lubricates  the  piston,  prevents  the  gas  escaping  behind  the 
piston,  and  absorbs  part  of  the  heat  evolved  in  the  cylinder  by  the 
compression  of  the  gas.  This  oil  is  separated  from  the  liquefied  am- 
monia by  gravity  in  separating  tanks  and  returned  to  the  compressor. 

The  machines  above  described  are  called  "  compression  ma- 
chines," because  the  volatile  substance  is  compressed  directly  to  be 
used  again.  Another  class  of  refrigerating  apparatus  depends  for 
the  recovery  of  the  volatile  substance  upon  absorption  of  the  vapors 


24 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


in  some  liquid  from  which  they  can  again  be  set  free.  The  cooling 
effect  in  this  case  is  also  produced  by  rapid  evaporation  of  the  lique- 
fied gas,  the  difference  in  the  two  classes  of  machines  being  in  the 
method  of  recovering  the  vaporized  liquid  for  use  again.  In  the 
Carre  ammonia  absorption  apparatus  very  concentrated  aqua  am- 
monia is  heated  in  an  iron  retort  or  generator ;  the  ammonia  gas  is 
driven  out  through  a  condenser,  chilled  by  running  water  over  the 
coils;  the  ammonia  is  liquefied  by  its  own  pressure,  and  the  liquid 
passes  through  an  expansion  valve  into  the  refrigerator  coils,  which 


COOLING  WATER. 


COOLING  WATCH. 


FIG.  16. 


EXPANSION 

COCK. 


may  be  surrounded  with  brine.  The  expanded  ammonia  vapor  then 
passes  to  the  absorber,  containing  weak  ammonia  water  from  the  gen- 
erator, which  has  been  cooled  by  running  through  coils  immersed  in 
water.  Reabsorption  of  the  ammonia  vapors  to  form  concentrated 
aqua  ammonia  takes  place,  and  the  solution  is  returned  to  the  generator 
to  repeat  the  cycle.  Another  style  of  absorption  machine  evaporates 
water  in  a  vacuum  apparatus,  and  absorbs  the  vapor  in  concentrated 
sulphuric  acid.  The  dilute  ac\d  thus  produced  is  concentrated  in  open 
pans  by  evaporating  the  water,  and  is  used  again. 

The  absorption  machines  require  a  large  quantity  of  cooling  water, 
and  are  generally  more  complicated  and  expensive  than  the  com- 
pression machines. 

A  third  class  of  machines  are  those  depending  on  the  sudden  ex- 


INTRODUCTION  25 

pansion  of  highly  compressed  air  or  other  gas,  which  does  not  liquefy 
at  the  temperature  and  pressure  used.  These  machines  are  large 
and  complicated  and  are  not  adapted  to  making  ice,  but  find  limited 
use  for  cooling  and  ventilating  on  board  war  vessels  where  any  traces 
of  ammonia  or  other  vapor  would  be  dangerous. 

Refrigeration,   Cold  Storage,    and    Ice-making,    A.    J.   Wallis-Taylor. 
London,  1902.     (Lockwood  &  Son.) 

•     SPECIFIC  GRAVITY 

By  the  specific  gravity  of  a  liquid  is  meant  its  relative  weight  com- 
pared with  the  weight  of  an  equal  volume  of  pure  water  at  a  definite 
temperature.  This  determination  is  one  of  the  most  frequent  opera- 
tions in  chemical  work  and  may  be  done  with  a  pyknometer  when 
very  exact  results  are  required,  but  in  technical  operations,  sufficient 
accuracy  for  all  practical  purposes  may  be  attained  by  the  hydrometer. 
This  is  usually  a  glass  instrument,  consisting  of  a  cylindrical  bulb, 
weighted  at  the  lower  end,  and  drawn  out  at  the  upper  end  to  a  long, 
slender  tube,  carrying  a  scale.  The  gradations  of  the  scale  begin  at 
the  top  and  read  downward,  the  numerically  greater  reading  being  at 
the  bottom,  except  in  one  instance,  —  that  of  Baume's  scale  for  liquids 
lighter  than  water.  Since  the  specific  gravity  of  a  liquid  varies  as  its 
temperature  changes,  the  scale  is  adjusted  to  a  certain  temperature, 
usually  about  15°  C.,  at  which  determinations  must  be  made. 

When  the  hydrometer  is  placed  in  a  liquid,  it  sinks  sufficiently 
to  displace  a  volume  of  the  liquid  equal  in  weight  to  the  weight  of 
the  instrument,  and  floats  in  an  upright  position.  Should  the  hy- 
drometer sink  so  deeply  into  the  liquid  that  the  scale  is  entirely  below 
the  surface,  the  specific  gravity  is  less  than  the  spindle  is  intended 
to  measure,  and  one  having  lower  *  numerical  readings  should  be  used. 
If,  on  the  contrary,  the  spindle  does  not  sink  deep  enough  to  bring 
the  scale  into  the  liquid,  an  instrument  having  higher  numerical  scale 
readings  is  necessary. 

Three  systems  of  hydrometer  scales  are  in  common  use,  besides  a 
great  number  of  special  scales  intended  to  give  one  particular  factor 
in  the  specific  gravity  of  a  liquid ;  e.g.  the  per  cent  of  alcohol  in  a 
mixture  of  alcohol  and  water,  or  the  amount  of  sugar  in  a  syrup,  etc. 

The  direct  specific  gravity  hydrometer  is  so  constructed  that  the 
reading  on  its  scale  shows  the  specific  gravity  of  the  liquid  directly 
as  compared  with  pure  water  at  the  same  temperature  (15°  C.).  Its 

*  Baume's  hydrometer  for  liquids  lighter  than  water  is  an  exception  (p.  27). 


26  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

scale  is  adapted  to  liquids  heavier  or  lighter  than  water.  The  point 
to  which  it  sinks  in  pure  water  at  15°  C.  is  marked  1.000.  As  usually 
furnished,  a  set  of  these  hydrometers  consists  of  four  spindles,  the 
scale  being  thus  divided  into  four  sections.  The  first  spindle,  with 
gradations  from  0.700  to  1.000,  is  for  liquids  lighter  than  water,  and 
the  others  are  for  those  heavier  than  water.  The  scale  is  usually 
divided  about  as  follows:  1.000  to  1.300  oh  the  second  spindle,  1.300 
to  1.600  on  the  third,  and  1.600  to  2.000  on  the  fourth. 

The  gradations  at  the  top  of  each  spindle  are  farther  apart  than 
those  at  the  bottom  of  the  stem,*  rendering  the  reading  somewhat 
more  difficult  in  dense  liquids  than  in  those  of  lighter  gravity. 

TwaddelTs  hydrometer  is  also  a  direct-reading  instrument.  The 
system  consists  of  a  series  of  spindles  (usually  six  in  number)  car- 
rying gradations  from  0  to  174.  The  reading  in  pure  water,  at 
15.5°  C.,  is  taken  as  0,  and  each  subsequent  rise  of  0.005  sp.  gr.  is 
recorded  on  the  scale  as  one  additional  division.  Thus  10  Twaddell 
becomes  1.050  sp.  gr.  The  gradations  on  this  scale  are  also  closer 
together  as  the  specific  gravity  increases,  but  as  its  total  length  is 
divided  among  six  spindles,  the  readings  are  not  so  difficult  even  at 
the  highest  gravities.  The  instruments  are  small,  and  may  easily 
be  used  in  an  ordinary  100  cc.  measuring  cylinder.  For  the  reasons 
that  it  is  easy  to  read,  requires  but  a  small  quantity  of  liquid  to  be 
tested,  and  permits  a  ready  conversion  of  its  readings  into  specific 
gravity  by  a  very  simple  calculation,  this  is  a  convenient  hydrom- 
eter for  ordinary  factory  or  laboratory  use.  It  is,  however,  hot  adapted 
to  liquids  lighter  than  water. 

Twaddell  readings  are  converted  into  specific  gravity  as  follows: 
Multiply  the  reading  by  .005  and  add  1.000  to  the  product.  Thus  15 
Twaddell  becomes  1.075  sp.  gr.  (1.000  +  [15  X  .005]  =  1.075.) 

Baume's  hydrometer  is  largely  used  in  technical  work,  but  its 
readings  bear  no  very  direct  relation  to  true  specific  gravity.  Baume 
dissolved  15  parts  of  pure  salt  in  85  parts  of  pure  water  at  12.5° 
C.  The  point  to  which  his  instrument  sank  in  this  solution  was 
marked  15 ;  the  point  to  which  it  sank  in  pure  water  was  marked  0. 
The  distance  between  these  points  was  divided  into  fifteen  equal  parts, 
and  the  entire  stem  marked  off  in  divisions  of  this  width.  This 
produced  an  instrument  for  liquids  heavier  than  water. 

For  liquids  lighter  than  water,  the  point  to  which  the  instrument 
sank  in  a  10  per  cent  solution  of  salt  was  marked  0,  and  that  to 

*  For  the  explanation  of  this  fact  consult  any  of  the  larger  works  on  physics. 


INTRODUCTION  27 

which  it  sank  in  distilled  water  was  marked  10 ;  the  distance  between 
these  points  was  divided  into  10  equal  parts,  and  this  gradation  con- 
tinued the  entire  length  of  the  spindle.  The  0  thus  being  placed  at 
the  bottom  of  the  stem,  the  lighter  the  gravity  of  the  liquid  tested, 
the  greater  numerically  is  the  reading  of  the  scale.  For  instance,  a 
liquid  reading  70  Be.  is  of  less  gravity  than  one  of  50  Be.,  which  in 
turn  is  lighter  than  water  at  10  Be. 

To  further  complicate  matters,  the  instrument  makers  have  pro- 
duced instruments  with  erroneous  scales.  A  test  made  a  few  years 
ago  disclosed  thirty-four  different  scales,  none  of  which  was  correct !  * 

The  conversion  of  Baume  readings  to  specific  gravity  involves 
some  calculation  and  is  usually  accomplished  by  reference  to  tables. 
The  formulae  for  this  conversion  are  as  follows  :  — 

g  ^  o  _  -j,  r  _      145  (for  liquids  heavier  than  water.    Tempera- 

sp.'  gr.        ture  60°  F.).f 

B^Q_    140         J^Q  (for  liquids  lighter  than  water.     Tempera- 
~sp.  gr.  ture  60°  F.).  V 

The  pyknometer  is  not  often  used  in  technical  work,  but  a 
brief  description  of  it  may  not  be  out  of  place  here.  It  consists  of 
a  small  bottle,  having  ground  into  its  neck  a  capillary  tube  enlarged 
at  its  upper  end,  to  form  a  reservoir  which  is  closed  by  a  stopper. 
The  tube  is  removed  and  the  bottle  filled  with  the  liquid  to  be  tested ; 
the  tube  is  then  inserted  tightly,  the  liquid  displaced  rising  through 
the  capillary  to  the  enlarged  part  of  the  tube.  The  stopper  is  then 
loosely  inserted  and  the  bottle  placed  in  a  bath  at  the  temperature 
at  which  the  gravity  is  to  be  taken.  When  the  bottle  and  contents 
have  reached  this  temperature,  the  stopper  is  taken  out  and  the  liquid 
in  the  reservoir  removed  by  means  of  absorbent  paper,  until  the  level 
of  the  liquid  recedes  within  the  capillary  to  a  mark  thereon.  The 
stopper  is  then  tightly  inserted  and  the  bottle  removed  from  the  bath, 
and  after  cleaning  and  drying  its  outside,  allowed  to  stand  until  it 
reaches  the  normal  temperature  of  the  room.  It  is  then  weighed, 
and  the  specific  gravity  of  the  liquid  is  calculated  from  its  known 
volume,  previously  determined  by  calibration  of  the  bottle.  (For 
determining  specific  gravity  by  means  of  the  pyknometer,  see  T.  E. 
Thorpe's  Dictionary  of  Applied  Chemistry,  Vol.  V,  pp.  107-114.) 

*  C.  F.  Chandler,  Proc.  Nat.  Acad.  Sciences,  1881. 

t  J.  Am.  Chem.  Soc.  21  (1889),  119.  J.  Soc.  Ind.,  1905  (24),  786. 

*  European  instrument  makers  use  the  formula  Be.  =  144.3 — .    See  Alkali- 

sp.  gr. 

makers'  Handbook  (Lunge  and  Hurter),  p.  175. 


28 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


Westphal's  balance  is  used  to  determine  the  specific  gravity  of 
liquids.  A  glass  plummet  of  known  weight  and  volume,  suspended 
from  the  beam  by  a  fine  platinum  wire,  is  submerged  in  the 
liquid.  The  weight  which  the  plummet  loses  by  this  submersion  is 
the  weight  of  the  volume  of  liquid  it  displaces.  The  decimal  gradua- 
tion of  the  beam,  with  the  use  of  riders  of  0.1,  0.01,  and  0.001  part  of 
the  weight  of  the  water  displaced  by  the  plummet,  permits  the  actual 
specific  gravity  to  be  read  off  on  the  beam,  as  soon  as  the  latter 
is  brought  to  equilibrium  with  the  plummet,  suspended  in  the  liquid  in 
question. 

SURFACE  PHENOMENA  AND  COLLOIDS 

Particles  in  the  interior  of  solids  and  liquids  are  greatly  influ- 
enced by  the  presence  in  their  immediate  neighborhood  of  other 
particles ;  this  is  indicated  by  describing  solids  and  liquids  as  "  con- 
densed phases."  Particles  on  the  surface  are  free  from  such  action 
on  one  side,  but  not  on  the  other.  Hence  the  properties  of  the  sur- 
face of  a  condensed  phase  are  different  from  those  of  the  interior; 
thus  an  aqueous  soap  solution  contains  more  soap  in  its  surface  layer 
than  in  its  interior,  but  with  most  inorganic  salts  the  reverse  is  true. 
The  surface  layers  are  so  thin,  however,  that  these  differences  become 
appreciable  only  when  the  ratio  of  surface  to  volume  is  enormous. 
This  obtains  when  a  substance  is  in  the  form  of  extremely  small, 
separate  particles;  since  the  voids  between  the  particles  are  neces- 
sarily filled  with  something,  such  a  system  consists  of  at  least  two 
phases.  The  whole  is  called  a  disperse  system  —  the  separated  par- 
ticles the  disperse  phase,  and  the  void-filling  substance  the  dispersing 
medium.  Surface  phenomena  are  usually  of  importance  only  in  such 
disperse  systems.  The  following  table  illustrates  the  phenomena  :  — 


DISPERSING  MEDIUM 

DISPERSE  PHASE 

ILLUSTRATION 

1 

Gas 

Liquid 

Fog 

2 

Gas 

Solid 

Smoke 

3 

Liquid 

Gas 

Whipt  Cream 

(Air  emulsified  in  oil.) 

4 

Liquid 

Liquid 

Emulsions  —  Cream 

(Oil  emulsified  in  water.) 

5 

Liquid 

Solid 

Suspensions  —  Colloidal 

solutions,  as  gold  in  water. 

6 

Solid 

Gas 

Bread 

7 

Solid 

Liquid 

Frozen  Cream  —  Gels    • 

8 

Solid 

Solid 

"Milk  "Glass 

INTRODUCTION  29 

When  the  size  of  the  dispersed  particles  is  small,  the  friction  be- 
tween them  and  the  gaseous  or  liquid  dispersing  medium  becomes  very 
great,  and  relative  motion  is  difficult.  Hence  separation  by  decan- 
tation  is  difficult  or  impossible,  nitration  fails  except  through  the 
densest  filtering  media,  and  the  separation  of  the  phases  is  a  serious 
problem.  Frothing  in  evaporators,  dust  production  in  furnacing  and 
grinding  operations,  the  "  fume  "  from  storage  batteries  and  pickle  baths, 
are  cases  in  point.  The  solution  of  the  problem  is  found  either  in  in- 
creasing relative  motion  by  the  application  of  an  external  force, 
(as  in  centrifugal  separators  for  dust,  cream,  etc.),  or  in  causing  co- 
alescence of  the  particles.  This  may  be  brought  about  by  enmeshing 
them  in  a  mass  of  larger  particles  (as  in  the  use  of  iron  or  aluminum 
hydroxides  in  water  purification),  by  impinging  upon  surfaces,  wet 
or  otherwise  (as  in  "  catch-alls  "  and  gas  washers),  or  by  electrical 
discharge,  or  by  mutual  co-precipitation.  These  last  two  methods 
are  based  on  the  fact  that  in  general  there  exists  at  the  surface  be- 
tween two  phases  an  electrostatic  potential  difference.  The  parti- 
cles of  the  dispersed  phase  are  therefore  charged  with  reference  to  the 
dispersing  medium  and  hence  are  capable  of  electrolysis  (movement 
in  an  electric  field  followed  by  discharge  on  reaching  the  electrode). 
Also  the  particles  are  often  held  apart  and  prevented  from  coalescing 
to  form  larger  aggregates,  by  the  mutual  repulsion  of  the  charges  on 
the  particles;  when  discharged,  coagulation  or  precipitation  results. 
Discharge  may  be  caused*  (a)  by  electrolysis ;  (6)  by  neutralization 
with  the  charge  of  a  disperse  phase  of  opposite  sign  ;  (c)  by  the  adsorp- 
tion of  ions  of  opposite  sign. 

A  characteristic  property  of  such  disperse  systems  is  the  power 
possessed  by  the  surfaces  between  the  phases  to  condense  upon 
themselves  large  quantities  of  gases  and  of  solutes  from  liquid  phases. 
This  condensation  is  called  adsorption;  the  amount  adsorbed  x,  on 

the  surface  m,  is  given  by  the  expression  —  =  kCn,  where  C  is  the 

Tflt 

*  An  illustration  of  (a)  is  the  Cottrell  Process  for  precipitating  smoke  and 
dust  from  smelters,  cement  works,  etc. ;  the  gas  containing  the  fine  solid  particles 
in  suspension  is  passed  through  a  cylindrical  metal  tube  or  chimney,  at  the  axis 
of  which  is  a  fine  wire.  Between  this  wire  and  the  chimney  a  high  direct-current 
potential  difference  (100,000  volts  and  over)  is  maintained,  which  causes  the 
charged  dust  particles  to  move  rapidly  to  the  surface  of  the  stack,  discharge,  and 
coalesce.  Owing  to  the  small  ratio  of  charge  to  weight  of  dust  particle,  the  cur- 
rent consumption  (hence  the  cost)  is  small.  The  efficiency  of  dust  removal  and 
the  gas-handling  capacity  are  high.  A  technical  application  of  (b)  is  in  the  tan- 
nage of  leather  (p.  577),  while  (c)  is  illustrated  in  the  use  of  certain  electrolytes *to 
coagulate  fine  precipitates  (the  use  of  salt  in  washing -white  lead,  p.  225,  and  the 
addition  of  NI^NO?  to  aid  in  filtering  phosphomolybdate  precipitate). 


30  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

concentration  of  the  substance  adsorbed,  while  k  and  n  are  constants, 
n  being  greater  than  unity,  seldom  less  than  2  or  more  than  20. 
Adsorption  at  low  concentration  is  relatively  far  greater  than  at  high, 
and  this  can  be  used  to  remove  small  amounts  of  impurities  from  solu- 
tions, as  in  water  purifying  (p.  49),  sugar  refining  (p.  429),  decoloriz- 
ing oils  (p.  342),  etc.  The  adsorbing  agent  may  be  brought  in  contact 
with  the  liquid  by  admixture  or  by  use  of  the  counter-current  prin- 
ciple, the  solid  being  held  in  a  suitable  container  through  which  the 
liquid  passes,  thus  forming  an  adsorption  filter.  Adsorption  is  gener- 
ally greater  the  lower  the  temperature  and  the  higher  the  molecular 
weight  and  complexity  of  the  substance  adsorbed.  Certain  materials, 
notably  bone-char  and  fuller's  earth,  have  high  adsorptive  power, 
while  others,  such  as  animal  and  vegetable  fibres,  are  very  specific  in 
the  substances  they  adsorb. 

Where  the  dispersing  medium  is  a  liquid,  the  disperse  phase  is  called 
a  colloid,  if  exceedingly  small,  so  that  separation  by  filtration  is  very 
difficult ;  if  somewhat  larger,  it  is  called  colloidal,  or  a  colloidal  precipi- 
tate or  suspension.  Solid  colloids  vary  much  in  their  capacity  to  com- 
bine with  the  solvent ;  the  following  aqueous  colloids  are  approximately 
in  the  order  of  their  degree  of  hydration  in  colloidal  solutions :  (1)  glue, 
caseinogen,  dextrins,  etc. ;  (2)  hide  substance,  starch ;  (3)  ferric 
hydroxide,  aluminium  hydroxide,  silicic  acid ;  (4)  clay ;  (5)  arsenic 
sulphide,  sulphur;  (6)  colloidal  metals  (gold,  etc.).  When  highly 
hydrated,  the  colloid  acquires  many  of  the  properties  of  a  liquid,  and 
the  colloidal  solution  resembles  an  emulsion.  Such  colloids  are  called 
emulsion  colloids  or  emulsoids;  the  less  hydrated  ones  are  called  sus- 
pensoids.  A  sharp  distinction  cannot  be  drawn  between  them. 

The  value  of  a  solid  colloid  depends  on  its  possession  of  emulsoid 
characteristics.  Solid  emulsoids  when  treated  with  a  solvent  first 
swell  (glue,  rubber,  starch),  due  to  combination  with  the  solvent, 
.but  finally  dissolve,  i.e.  the  individual  particles  separate  and  stay 
in  suspension  in  the  solvent.  By  lowering  the  temperature,  the 
solvent  in  combination  with  the  colloid  increases  at  the  expense  of 
that  in  the  dispersing  medium,  and  if  $ie  latter  be  not  too  great  in 
amount,  it  finally  becomes  so  small  relative  to  the  colloidal  phase  that 
the  two  change  functions,  i.e.  the  system  becomes  a  suspension  of 
small  drops  of  liquid  dispersed  in  a  solid,  much  swollen  with  solvent. 
This  is  called  a  gel  or  jelly,  and  the  transformation  temperature  is  the 
jellying  point. 

Solid  colloids  are  substances  whose  individual  particles  or  mole- 
cules are  very  large  and  complex  molecular  aggregates.  They  are 


INTRODUCTION  31 

in  general  chemically  inert  and  little  affected  by  solvents ;  when  heated, 
or  when  swollen  with  a  suitable  solvent  (in  gel  form),  they  are  "  plas- 
tic," i.e.  they  can  be  moulded,  and  separate  pieces  pressed  together 
coalesce  so  they  can  be  shaped  at  will.  Some  possess  great  strength 
and  hardness  and  are  important  as  materials  of  construction.  Such 
colloids  consist  of  one  or  several  units  U,  a  number,  n,  of  which  are 
associated  into  an  aggregation  Un.  Thus  in  starch  the  unit  is  the 
dextrose  radical,  association  resulting  from  elimination  of  water  from 
dextrose ;  in  rubber  the  unit  is  isoprene  or  polyprene ;  in  albumens 
the  units  are  a  number  of  amido-acids.  In  general  the  larger  the 
aggregate  Un,  the  stronger  and  harder  the  solid  colloid,  the  more 
inert  chemically,  the  less  soluble  in  solvents,  and  the  less  ductile  and 
plastic  the  material  becomes.  Mechanical  manipulation,  heat,  and 
the  action  of  solvents  tend  to  decrease  the  size  of  the  aggregate  by  de- 
creasing n. 

Many  important  solid  colloids  (cellulose,  hair,  wool,  and  silk)  are 
natural  products,  any  chemical  treatment  of  which  causes  disinte- 
gration of  the  aggregate  to  a  greater  or  less  extent,  with  results  on  the 
physical  properties  as  indicated  (pp.  489,  494,  499,  505,  511,  etc.). 
Many  others  are  made  by  first  forming  the  colloid  as  a  plastic  and 
then  destroying  the  plastic  condition.  The  important  industrial 
methods  of  doing  this  are:  (1)  producing  the  plastic  state  by  means 
of  heat  and  hardening  by  cooling  (as  in  glass,  p.  196,  and  asphalt, 
p.  347) ;  (2)  rendering  plastic  with  a  solvent  and  solidifying  by  evapo- 
ration of  the  solvent  (as  in  artificial  silk,  p.  496,  and  sun-dried  bricks) ; 
this  may  be  succeeded  by  chemical  changes  essentially  modifying  the 
character  of  the  solid  (drying  of  varnish,  p.  397 ;  burning  of  ceramics, 
p.  212) ;  (3)  increasing  the  chemical  and  physical  resistance  and  de- 
creasing the  plasticity,  by  increasing  the  size  of  the  molecular  aggre- 
gate Un,  by  (a)  co-precipitating  two  emulsoids  to  give  a  more  com- 
plex and  stable  mass  (as  in  tanning  leather,  p.  573) ;  (6)  by  increasing 
the  number  of  units,  n,  in  each  aggregate  (as  in  the  manufacture  of 
bakelite,  p.  585) ;  (c)  by  increasing  the  complexity  of  the  unit  U  by 
chemical  addition  (as  in  vulcanizing  rubber,  p.  588). 


FUELS 

Fuels  are  substances  which,  when  burned  with  air,  evolve  heat 
with  sufficient  rapidity  and  in  sufficient  quantity  to  be  employed 
for  domestic  or  industrial  purposes. 

There  are  three  classes  of  fuel :  solid,  liquid,  and  gaseous.  In  the 
majority  of  these  the  essential  constituent  is  carbon,  but  in  many  of 
them  hydrogen  is  also  an  important  ingredient.  In  rare  cases  sul- 
phur, phosphorus,  silicon,  or  manganese  may  take  part  in  the  com- 
bustion ;  but  for  the  purposes  for  which  fuel  is  ordinarily  used  these 
constituents  are  deleterious.  Oxygen  is  sometimes  regarded  as 
advantageous,  but  not  always.  Nitrogen  may  cause  a  direct  loss  of 
calorific  power,  owing  to  its  dilution  of  the  combustible  gases,  but 
in  most  solid  fuels  the  percentage  of  nitrogen  is  so  small  that  its 
effect  is  negligible. 

SOLID  FUELS 

The  solid  fuels  are  wood  and  other  matter  containing  cellulose, 
peat,  lignite  or  brown  coal,  bituminous  coal,  anthracite,  charcoal, 
and  coke. 

Wood  consists  of  cellulose  (CeHioOs)^  lignine,  resins,  various 
inorganic  salts,  and  water.  The  quantity  of  water  present  has 
great  effect  on  the  heating  value  and  ranges  from  25  to  50  per  cent 
in  green  wood,  and  from  10  to  20  per  cent  in  air-dried  wood.  Wood 
cut  in  the  spring  and  summer  contains  more  water  than  that  cut 
in  the  early  part  of  the  winter.  A  cord  of  hard  wood,  such  as  ash 
or  maple,  is  about  equal  in  heating  value  to  one  ton  of  bituminous 
coal ;  soft  woods,  such  as  pine  and  poplar,  have  less  than  half  this 
amount.  Wood  burns  with  a  long  flame  and  makes  comparatively 
little  smoke ;  but  its  calorific  power  is  low,  averaging  from  3000  to 
4000  Cal.  per  kilo  of  air-dried  wood.  It  is,  however,  easily  kindled, 
the  fire  quickly  reaches  its  maximum  intensity,  and  a  relatively  small 
quantity  of  ash  is  formed.  Wood  is  too  expensive  for  industrial  use, 
except  in  a  few  special  cases,  where  freedom  from  dirt  and  smoke  is 
necessary. 

Of  other  cellulose  materials,  shavings,  sawdust,  and  straw  are 
used  for  fuel  in  some  places.  They  are  bulky  and  difficult  to  handle, 
while  their  heat  value,  which  depends  on  the  amount  of  moisture 
they  contain,  is  seldom  more  than  from  one-third  to  one-half  that 

32 


FUELS  33 

of  good  coal.  Such  waste  matter  as  spent  tan-bark  and  bagasse 
(crushed  sugar  cane),  and  the  pulp  from  sugar  beets  is  sometimes 
used  for  fuel  for  evaporation  or  for  steam,  but  owing  to  the  large 
amount  of  moisture  they  contain,  the  heat  value  is  very  low. 

Peat  is  the  product  of  slow  decay  of  mosses,  especially  Sphag- 
nacece,  under  water.  It  is  of  little  importance  in  this  country,  but 
is  extensively  used  in  parts  of  Europe  where  it  is  found.  Since  it 
contains  a  large  amount  of  water  and  inorganic  matter,  its  calorific 
power  is  not  high,  averaging  from  4000  to  5000  Cal.  per  kilo.  One 
pound  of  peat  evaporates  about  4.5  Ibs.  of  water.  It  is  dug  from 
the  bogs  and  dried  in  the  air,  sometimes  being  heavily  compressed  to 
reduce  its  bulk.  As  thus  prepared,  it  contains  from  15  to  20  per  cent 
of  moisture  and  from  8  to  12  per  cent  ash.  It  is  used  considerably 
as  a  packing  material,  owing  to  its  soft  and  spongy  consistency. 

Lignite  or  brown  coal  is  intermediary  between  peat  and  bitu- 
minous coal.  It  was  probably  formed  from  swamp  plants  which 
decomposed  under  water,  and  is  geologically  of  more  recent  forma- 
tion than  true  coal.  It  is  dark  brown  or  black  in  color,  and  its  text- 
ure is  fibrous,  earthy,  or  sometimes  vitreous.  It  usually  contains 
from  15  to  20  per  cent  of  moisture,  a  large  quantity  of  ash,  and  often 
a  considerable  amount  of  sulphur.  It  burns  freely  with  a  long 
flame,  producing  much  smoke,  and  its  calorific  power  varies  from  4000 
to  6500  Cal.  It  is  extensively  used  for  heating  steam  boilers  and 
evaporating  pans,  and  for  domestic  fires. 

Bituminous  coal  is  the  most  important  of  all  fuels.  There  is 
a  great  variety  in  the  kinds  of  coal  classed  under  this  name,  but 
they  differ  chiefly  in  the  amount  of  volatile  matter,  which  ranges 
from  20  to  50  per  cent.  They  were  all  formed  from  similar  sources, 
the  varieties  having  resulted  from  pressure  and  from  exposure  to 
heat.  The  specific  gravity  varies  from  1.25  to  1.75.  They  are  classi- 
fied according  to  their  behavior  when  burning,  as  fat,  caking,  and 
non-caking.  Fat  coals  usually  have  a  dull  lustre,  are  very  rich  in 
volatile  matter,  sometimes  containing  as  much  as  50  per  cent,  and 
burn  with  a  long,  smoky  flame,  sometimes  caking  in  the  fire.  Non- 
caking  coals  are  those  which  burn  freely,  with  little  smoke,  and  do 
not  cake.  The  caking  coals  burn  with  a  smoky  flame  and  fuse  or 
sinter  together. 

The  formation  of  coal  is  probably  due  to  a  slow  decomposition 
of  cellulose  matter,  under  fresh  water,  by  which  marsh  gas  (CHO  and 
carbon  dioxide  (CO2)  were  eliminated.  The  composition  of  a  typi- 
cal coal,  as  shown  by  the  analysis  of  good  samples,  may  be  repre- 


34 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


sented  by  the  symbol  (C26H20O2),  and  assuming  this,  the  change  of 
cellulose  may  be  represented  by  the  equation :  — 

6  (C6HioO5)  =  3  CH4  +  7  CO2  +  14  H2O  +  C26H20O2. 

Various  changes  were  afterwards  brought  about  by  the  heat  and 
pressure  within  the  earth's  strata,  and  the  character  of  the  coals 
modified  in  many  cases.  Thus,  more  or  less  of  the  volatile  constit- 
uents were  removed,  and  the  coal  itself  compressed  to  a  very  hard, 
compact  mass.  When  this  process  went  to  the  extreme,  nearly  the 
whole  of  the  volatile  constituents  were  expelled,  and  the  resulting 
product  is  the  hard  coal  known  as  anthracite. 

Anthracite  coals  are  nearly  pure  carbon,  are  very  hard  and  dense, 
have  a  very  high  lustre,  and  contain  but  little  hydrogen  or  volatile 
matter.  They  burn  with  a  slight  flame,  form  no  smoke,  have  no 
caking  properties,  and  are  difficult  to  ignite.  Their  specific  gravity 
is  high,  being  nearly  1.75  in  good  Lehigh  coal.  They  have  a  calorific 
value  of  from  7500  to  8500  Cal. 

Between  bituminous  and  anthracite  coals  are  a  number  of  semi- 
anthracites,  which  cannot  be  classed  in  either  variety. 

Coal  deteriorates  considerably  when  stored,  owing  to  the  escape 
of  some  of  its  volatile  constituents.  There  is  a  popular  idea  that 
wetting  coal  before  burning  increases  its  heating  capacity ;  but  this 
is  a  fallacy,  for  a  loss  of  heat  results. 

The  average  composition  o*f  various  coals  is  here  tabulated  for 
comparison :  —  * 


TOTAL 
CARBON 

FIXED 
CARBON 

VOLATILE 
MATTER 

ASH 

MOISTURE 

CALORIES 

Brown  coal  (Wyo.)     .     . 

58.41 

39.56 

37.96 

4.79 

17.69 

5753 

Bituminous  (111.)    .     .     . 

63.85 

44.31 

37.70 

12.80 

5.13 

6496 

Bituminous  (Pa.)  .     .     . 

76.34 

60.85 

29.09 

9.09 

0.97 

7751 

(Connellsville) 

Semi-bituminous  (W.  Va.) 

79.12 

70.80 

16.90 

11.50 

0.80 

7761 

(Pocahontas) 

Anthracite  (Pa.) 

84.28 

3.27 

9.13 

3.33 

7417 

Charcoal  is  made  by  the  dry  distillation  of  wood,  at  a  tempera- 
ture of  from  400°  ,to  450°  C.  This  is  done  in  heaps,  or  in  closed 
retorts.  All  the  volatile  matter  is  driven  off,  and  the  residue  con- 
sists of  carbon  and  the  inorganic  constituents  of  the  wood.  Good 
charcoal  is  porous,  brittle,  with  conchoidal  fracture,  and  retains  the 
*  U.  S.  Bureau  of  Mines,  Bui.  No.  29. 


FUELS 


35 


form  of  the  wood,  but  has  only  about  three-fourths  of  the  volume 
and  usually  about  20  per  cent  of  the  weight  of  wood.  It  burns  with 
but  slight  flame,  without  smoke,  and  is  easily  ignited.  Containing 
but  little  sulphur  or  phosphorus,  it  is  especially  useful  in  making 
some  high  grades  of  iron  and  steel.  Its  calorific  power  is  about 
7100  Cal. 

In  this  country  much  of  the  charcoal  is  made  by  burning  wood 
in  "  charcoal  pits."  The  wood  is  heaped  in  a  hemispherical  pile 
around  a  central  opening,  and  covered  with  earth  and  sod,  leaving 
only  a  few  small  draught  holes  near 
the  bottom.  Then  it  is  ignited  at 
the  centre  and  allowed  to  burn 
until  the  whole  pile  is  on  fire.  A 
smouldering  combustion  takes  place, 
largely  at  the  expense  of  the  oxygen 
and  hydrogen  of  the  wood  fibre, 
forming  water,  carbon  dioxide,  and 
volatile  hydrocarbons,  which  escape. 
The  draught  holes  are  then  all  closed 
and  the  pit  is  kept  carefully  covered 
until  the  fire  smothers  and  the  char- 
coal is  cold.  By  carbonizing  in  pits 
nearly  all  the  volatile  matter  is  lost, 
or  at  best,  only  a  part  of  the  tar  is 
saved  and  the  yield  of  charcoal  is 
only  20  per  cent  by  weight  of  the 
wood.  But  if  the  process  is  carried 
on  in  retorts,  a  large  amount  of  gas, 
pyroligneous  acid,  and  tar  is  col- 
lected (see  p.  301),  and  about  30  per  cent  of  charcoal  is  obtained, 
together  with  nearly  40  per  cent  of  pyroligneous  acid  and  4  per  cent 
of  tar. 

Coke  is  made  by  the  destructive  distillation  of  coal.  It  has  a 
silvery  white  lustre,  an  open,  porous  structure,  and  a  metallic  ring 
when  struck.  It  contains  all  the  ash-forming  materials  of  the  coal, 
but  nearly  all  volatile  matter  and  sulphur  have  been  eliminated. 
For  metallurgical  purposes  it  must  be  sufficiently  strong  to  sustain 
the  weight  of  the  charge  in  the  furnace  without  crushing.  The 
calorific  value  is  from  7600  to  8100  Cal.  It  burns  without  smoke  and 
with  but  little  flame  and  does  not  cake.  It  is  made  in  kilns  of  two 
general  types :  The  "  bee-hive  "  coke  oven  (Fig.  17)  is  made  of 


FIG.  17. 


36 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


brick,  with  a  circular  opening  (A)  at  the  top  and  a  door  (B)  at  the 
side,  through  which  the  coke  is  drawn.  A  part  of  the  coal  is  burned, 
in  order  to  carbonize  the  remainder.  As  a  rule,  no  attempt  is  made 
to  save  the  volatile  products  or  the  tar.  The  yield  of  coke  amounts 
to  only  60  or  65  per  cent  of  the  weight  of  the  coal. 

Coking  ovens  in  which  the  by-products  are  saved  are  much  used 
abroad,  and  to  an  increasing  extent  in  this  country.  There  are  sev- 
eral kinds,  but  the  Otto-Hoffmann,  the  Simon-Carves,  and  the  Semet- 
Solvay  ovens  are  much  used.  In  these,  the  ammonia  and  coal  tar  are 
recovered,  and  a  coke  suitable  for  metallurgical  purposes  is  obtained. 
The  waste  gas  is  employed  to  heat  the  retorts. 


HUM  l^llllim  •••!•••  Ps3illil  I 


FIG.  18. 

The  Otto-Hoffmann  oven  is  shown  in  Fig.  18.  The  retorts  are 
narrow  chambers  (O)  about  40  feet  long,  5  feet  high,  and  22  inches 
wide,  having  doors  at  each  end,  and  heated  by  vertical  flues  (T,  T) 
in  the  walls.  Coal  is  charged  through  (F,  F)  while  the  gases  and 
tar  pass  off  through  (A,  A)  to  the  hydraulic  main  (V,  V).  The  gas 
for  heating  enters  from  pipe  (G),  mixes  with  hot  air  from  the  re- 
generator (R),  and  burns  in  the  flue  (S)  under  the  retorts,  the  flame 
passing  up  through  the  flues  (T,  T),  and  down  through  (T',  T')  to 
(S'),  from  which  the  products  of  combustion  pass  through  the  regen- 
erator (R')  and  heat  it.  After  a  time,  the  flow  of  gases  is  reversed, 
the  producer  gas  enters  through  (G')  and  air  through  (R'),  burning 
together  in  (S')>  while  the  products  of  combustion  escape  through 
(R).  The  volatile  matter  given  off  from  the  coal  passes  through 
(V)  to  washers  and  scrubbers  (see  Illuminating  Gas),  which  remove 
tar  and  ammonia,  while  the  gas  is  stored  in  a  holder,  to  be  led,  later, 
through  (G,  G'),  and  burned  under  the  retorts. 

The  Simon-Carves  oven  (Fig.  19)  is  also  a  long,  narrow  retort  (A) 
with  doors  at  each  end,  but  the  heating  flues  (F,  F)  are  set  hori- 
^ontally  in  the  retort  walls.  The  volatile  matter  escapes  from  the 


FUELS 


37 


retort  through  (B),  passes  to  the  washer  and  scrubber,  whence  the 
purified  gas  goes  to  the  holder,  from  which  it  is  drawn  as  needed, 
through  (G),  and  burned  with  hot  air. 


The  Semet-Solvay  oven  (Fig.  20)  also  has  horizontal  flues,  but 
deeper  and  narrower  retorts  than  the  two  just  mentioned.  Each 
retort  has  an  independent  set  of  flues  which  are  placed  in  the  retort 
lining  and  backed  by  a  heavy  brick  retaining  wall ;  this  supports  the 
weight  of  the  roof  arch,  and  also  holds  the  heat  during  the  drawing 
and  charging  of  the  retort.  Thus  the  flue  walls  can  be  made  much 
thinner  than  in  the  ovens  previously  mentioned,  and  the  oven  works 


A  -  Charging  Holes  D  -  Chimney  Canal 

B  -  Gas  uptake  p  .  Heating  Flues 

C  -  Gas  Inlet  to  Heating  Flues    R  -  Wall  between  Retorts 

FIG.  20. 

more  rapidly,  giving  a  larger  yield  of  coke,  and  will  coke  coals  which 
are  low  in  volatile  matter.  The  lining  can  easily  be  replaced  without 
rebuilding  the  entire  oven.  The  retorts  are  usually  about  30  feet  long 
by  16  inches  wide,  and  5J  feet  deep,  and  hold  about  4|  tons  of  coal 
at  each  charge.  No  regenerative  heating  is  used,  the  heat  being  re- 
tained in  the  walls  between  the  retorts.  A  number  of  these  ovens  have 
been  recently  introduced  into  this  country  and  give  excellent  results. 


38  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

« 

LIQUID  FUELS 

The  most  important  liquid  fuels  are  crude  petroleum  and  various 
oily  residues  obtained  in  distilling  petroleum,  shale  oil,  and  coal  tar. 

Crude  petroleum,  especially  the  Texas  and  California  oils,  and 
the  residuum  from  the  manufacture  of  burning  oils  and  lubricators, 
are  the  chief  sources  in  this  country.  The  residuum  from  Russian 
petroleum,  called  "  astatki,"  is  very  extensively  used  in  southern 
Russia. 

Crude  petroleum  is  easily  regulated  so  as  to  burn  without  smoke 
or  soot,  giving  a  steady  heat  and  requiring  no  stoking.  It  is  less 
bulky,  and  from  two  to  two  and  a  half  times  as  efficient  as  anthracite 
coal.  Its  heat  value  is  about  11,000  Cal.;  and  it  evaporates  about  15 
Ibs.  of  water  to  one  pound  of  oil.  One  pound  of  coal-tar  residue 
evaporates  13  Ibs.  of  water. 

Liquid  fuel  is  coming  into  more  general  use  every  year,  espe- 
cially where  long  flame  and  high  temperature  are  desired.  It  is 
usually  burned  as  spray,  being  forced  into  the  furnace  by  a  large 
atomizer  supplied  with  an  air  blast  or  superheated  steam. 

GASEOUS  FUELS 

Gas  fuel  is  important  industrially,  because  of  the  cleanliness, 
economy  of  labor,  and  exact  control  of  the  heat  it  affords,  and  of  the 
much  greater  efficiency  obtained  in  the  conversion  of  energy  into 
work,  or  the  development  of  power,  by  the  use  of  internal-combustion 
engines.  Since  combustible  natural  gas  is  found  only  in  restricted 
areas,  artificial  fuel  gas  is  largely  prepared ;  but  always  from  solid  fuels. 
Liquid  fuel  is  itself  nearly  as  satisfactory  as  gas,  and  is  too  expensive 
as  a  material  for  gas  making. 

Natural  gas  exists  already  formed  in  the  earth,  and  is  obtained 
by  boring  tube  wells  similar  to  petroleum  wells.  Its  essential  heat- 
producing  constituents  are  methane  (CH4)  and  hydrogen.  It  is  the 
cheapest  and  most  efficient  of  all  fuels,  when  properly  burned,  hav- 
ing a  heat  value  of  about  9400  Cal.  per  cubic  metre ;  but  it  requires  a 
large  amount  of  air  for  its  combustion,  and  special  burners  must  be 
used. 

Destructive  distillation  of  solid  fuels  containing  a  large  propor- 
tion of  volatile  matter  is  the  simplest  method  of  obtaining  combus- 
tible gases.  This  is  done  with  both  wood  and  soft  coal,  but  in  the 
case  of  the  former  the  expense  precludes  its  use  for  gas  production 
alone. 


FUELS  39 

Coal  gas  (p.  314)  is  made  by  distilling  bituminous  coal  in  retorts 
at  such  high  temperature  that  the  hydrocarbon  constituents  break 
down,  chiefly  into  methane  and  hydrogen  (about  40  per  cent  of  each), 
with  small  amounts  of  carbon  monoxide,  carbon  dioxide,  nitrogen, 
and  unsaturated  hydrocarbons  which  give  luminosity  to  the  flame. 
It  is  primarily  made  for  illumination,  but  is  often  used  for  power  and 
heating,  where  cheaper  gas  is  not  available. 

Gas  formation  is  important  in  the  burning  of  soft  coal,  since  dis- 
tillation results  from  the  heat  of  the  fire,  and  the  gases  set  free  in  the 
furnace  burn  with  a  "  long  flame,"  developing  their  heat  of  combus- 
tion uniformly  along  the  entire .  length  of  the  furnace. 

Besides  the  gas  from  the  volatile  constituents,  the  carbon  of  coal 
may  be  converted  into  a  combustible  gas,  carbon  monoxide,  by  burn- 
ing the  carbon  with  a  limited  air  supply.  A  disadvantage  of  the  pro- 
cess lies  in  the  fact  that  the  large  heat  of  formation  of  carbon  mon- 
oxide (29.0  Cal.  per  Mol),  is  developed  as  sensible  heat  in  the  gas 
and  is  lost  if  the  gases  are  cooled  previous  to  their  combustion. 
But  if  the  hot  gas  can  be  used  immediately  without  cooling,  as  is 
often  done  in  lime  kilns,  etc.,  there  is  much  economy  attained.  This 
may  be  considered  as  a  type  of  "  long-flame  burning  "  of  the  coal. 

Water  gas  contains  much  carbon  monoxide  and  is  made  by  the 
action  of  steam  on  carbon  at  high  temperature :  — 

C  +  H2O  =  H2  +  CO  -  29.0  Cal. 

There  is,  however,  a  very  large  absorption  of  heat  (29.0  Cal.)  in  this 
operation.  But  the  gas  has  high  calorific  value,  and  after  "  enrich- 
ment" (i.e.  saturation  with  low-boiling,  unsaturated  hydrocarbons), 
is  much  used  in  this  country  as  an  illuminant  (p.  312). 

It  appears  that  carbon  when  burned  with  oxygen  first  forms  car- 
bon dioxide  with  evolution  of  97.0  Cal.,  but  in  the  presence  of  excess 
carbon,  the  dioxide  is  partially  reduced  to  monoxide,  thus :  — 

C  +  CO2  =  2  CO  -  39  Cal. 

The  lower  the  temperature  the  less  complete  is  the  reduction.  By 
the  mass  action  law,  at  any  given  temperature,  the  partial  pressure 
of  the  carbon  dioxide,  divided  by  the  square  of  that  of  the  carbon 
monoxide,  is  at  equilibrium  a  constant,  which  is,  however,  a  function 

of   the  temperature;    i.e.     P00*  0  =  Ki  =  fi(f).      In  the  table  below 

(Pco)-2 

the  value  of  this  constant  for  various  temperatures  is  given,  and  it 
appears  that  a  large  reduction  of  dioxide  with  carbon  is  only  possible 


40 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


at  high  temperatures.  The  proportion  of  carbon  dioxide  in  the  gases 
at  a  given  temperature  is  generally  greater  than  the  figures  indicate, 
since  the  rate  of  reaction  between  carbon  dioxide  and  carbon  is  rela- 
tively low ;  but  it  decreases  rapidly  with  the  temperature.  If  the 
gases  are  in  contact  with  carbon  for  a  sufficient  time,  at  the  given 
temperature,  the  ratio  of  dioxide  to  monoxide  corresponds  to  the 
equation,  independently  of  the  presence  of  other  gases. 

EQUILIBRIUM    RELATIONSHIPS   OVER   CARBON  * 

(Pressures  in  Atmospheres) 


TEMPERATURE  OP 

Pco, 

too 

CARBON,  C° 

P*co 

PCO-P& 

700° 

1.37 

0.769 

800 

0.189 

0.165 

900 

0.0357 

0.0446 

1000 

0.00855 

0.0143 

1100 

0.00246 

0.00524 

1200 

0.000824 

0.00213 

1400 

0.000129 

0.000449 

The  mass  action  law  for  the  water-gas  reaction  requires  that 
H2°     =  KZ  =  fz(t)  ;    this   second   constant   is   also   shown  in   the 


table  above.  From  this  it  appears  that  at  high  temperatures  only 
does  the  reduction  of  the  steam  approximate  completion.  Since  the 
carbon  monoxide  formed  by  this  reaction  is  necessarily  accompanied  by 
carbon  dioxide  corresponding  to  its  equilibrium  with  carbon,  it  is  seen 
that  at  high  temperatures  only  will  the  gas  coming  from  the  producer 
be  satisfactory,  while  at  lower  temperatures  much  undecomposed  steam 
and  carbon  dioxide  will  be  present.  This  is  shown  in  the  table  below. 


THEORETICAL  COMPOSITION   OF   WATER-GAS 
(Equilibrium  of  Steam  and  Carbon) 


TEMPERATURE  OP 
CARBON,  C° 

%CO 

%H2 

%H20 

%C02 

800 

35.03 

39.67 

22.98 

2.32 

1000 

49.51 

49.93 

0.35 

0.21 

*  Haber,   Thermodynamics  of  Technical  Gas  Reactions. 


FUELS  41 

The  water  vapor  will  largely  separate  on  cooling  the  gas,  but  the 
carbon  dioxide  remains  as  an  undesirable  diluent.  Furthermore,  a 
commercial  producer,  especially  when  forced  in  capacity,  owing  to 
incomplete  reactions,  gives  lower  yields  of  monoxide  and  hydrogen 
than  is  shown ;  it  should  not  be  run  at  less  than  1000°  C. 

In  operation,  the  fuel  is  brought  to  white  heat  by  an  air  blast, 
which  is  then  cut  off  and  steam  injected ;  the  formation  of  water 
gas  now  proceeds  until  the  temperature  falls  below  1000°  C.,  owing 
to  heat  absorption ;  then  the  steam  is  cut  off,  and  the  air  blast  turned 
on  until  the  fuel  is  again  incandescent,  and  the  cycle  of  operations 
repeats.  During  the  air  blow,  the  gas  formed  is  sent  to  the  chimney 
but  during  the  steam  blow,  the  water  gas  is  cooled  and  sent  to  the 
holder.  As  the  fuel  bed  is  deep  and  above  1000°  C.,  the  air  blow 
forms  a  large  amount  of  carbon  monoxide,  which  may  be  collected  for 
use ;  but  it  is  often  run  to  waste,  in  which  case  the  air  supply  should 
be  large  to  secure  a  maximum  formation  of  carbon  dioxide,  which  is 
not  in  contact  with  the  fuel  a  sufficient  time  for  reduction  to  carbon 
monoxide.  Even  under  the  best  conditions,  a  serious  loss  of  heat  re- 
sults from  the  incomplete  combustion  of  the  fuel.* 

The  waste  of  energy  of  the  coal  in  this  intermittent  process  can 
be  largely  avoided  by  combining  the  two  reactions ;  the  air  and  steam 
being  regulated  so  the  heat  of  combustion  of  the  carbon  with  the  air 
just  compensates  the  heat  of  formation  of  the  water  gas ;  the  mixture 
of  gases  so  obtained  is  called  producer  gas.  The  product  contains 
much  free  nitrogen,  but  the  simplicity  of  the  process  causes  this  arti- 
ficial gas  to  find  use  on  a  large  scale. 

Since  the  fuel  must  be  kept  at  about  1000°  C.  to  secure  complete 
reaction  between  the  carbon  and  steam,  and  ensure  low  carbon 
dioxide  content  of  the  gas,  the  product  leaving  the  generator  carries 
very  high  sensible  heat.  In  theory  it  is  possible  to  recover  this  by 
using  it  to  heat  the  air  and  steam  supply,  thus  saving  energy  which 
must  otherwise  be  furnished  by  burning  more  coal,  but  owing  to  the 
complications  of  the  system,  this  heat  recovery  is  not  usually  prac- 
tised. 

The  use  of  steam  in  a  producer  to  lower  the  temperature  results 
in  smaller  loss  of  sensible  heat  in  the  gas,  and  theoretically  should 
increase  the  efficiency  of  the  gas  producer.  But  in  fact  the  gain  is 

*  Anthracite  produces  a  higher  content  of  hydrogen  and  methane  than  does 
coke,  but  the  latter  yields  some  methane,  due  to  the  action  of  hydrogen  on  the 
carbon  at  the  high  temperature.  The  gas  also  contains  some  nitrogen  from  the  air 
blast  and  often  a  little  oxygen  due  to  leaks. 


42  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

offset  by  the  large  heat  loss  due  to  undecomposed  steam,  which 
escapes  reduction  by  the  carbon,  owing  to  the  slow  rate  of  reaction 
between  steam  and  carbon;  much  heat  is  wasted  in  bringing  this 
steam  up  to  the  temperature  of  the  producer.  Since  lowering  the 
temperature  avoids  clinkering  of  the  ash  and  decreases  the  wear  and 
tear  on  the  apparatus,  steam  is,  however,  always  used  in  excess. 

In  the  Siemens  gas  producer  *  (Fig.  21),  the  coal  is  introduced 
at  (E),  falls  upon  the  step  grate  (B,  B),  and  is  brought  to  incan- 
descence by  air  entering  through  the  openings  while  steam  is  injected 


FIG.  .21. 


Fio.  22. 


from  the  pipe  (C),  and  the  gas  formed  escapes  through  (A,  A).  The 
ashes  fall  through  the  grate  (G)  into  the  pit,  which  is  kept  closed 
except  when  cleaning.  A  more  modern  producer  (Taylor's)  is  shown 
in  Fig.  22.  The  coal  rests  on  a  bed  of  ashes  (A,  A),  and  air  is  forced 
through  the  blast  pipe  (F),  raising  the  fuel  to  incandescence.  The 
gas  formed  passes  out  by  the  pipe  (E).  The  grate  (G)  is  made  to 
revolve  by  the  crank  at  (B),  and  the  ashes  fall  over  the  edge  of  the 
grate  at  (H).  The  bed  of  ashes* is  kept  about  3  feet  deep  on  the 
revolving  bottom.  Steam  from  the  pipe  (D)  is  introduced  with 
the  air  through  the  blast  pipe,  which  is  provided  with  a  hood  to 
disseminate  them  through  the  fuel.  In  all  plants  burning  producer 
gas  the  regenerative  or  recuperative  heating  system  is  used. 

*  Jour.  Soc.  Chem.  Industry,  1885,  441. 


FUELS  43 

Mond  gas  is  producer  gas  made  from  coal  slack  and  with  a  very 
large  excess  of  steam  in  the  blast.  Much  undecomposed  steam  passes 
out  with  the  gas  and  the  temperature  in  the  producer  is  kept  low 
(exit  gas  about  500°)  so  that  the  major  reaction  taking  place  is, 

C  +  2  H20  =  CO2  +  2  H2. 

This  avoids  destruction  of  the  ammonia  content  of  the  gas,  which  is 
higher  than  in  water  gas,  and  by  scrubbing  with  water  and  sulphuric 
acid,  ammonium  sulphate  is  obtained  as  a  by-product.  The  gas  has, 
however,  rather  low  calorific  value  (140  B.  T.  U.  per  cu.  ft.)  and  be- 
cause of  its  high  hydrogen  content  is  not  well  suited  for  open-hearth 
steel  furnaces. 

Blast  furnace  gas.  —  The  waste  gases  from  iron  blast  furnaces 
contain  about  30  per  cent  of  carbon  monoxide  and  58  to  60  per  cent 
of  nitrogen.  About  one-half  of  the  gas  is  used  for  heating  the  air 
blast  and  the  rest  under  boilers,  or  in  large  gas  engines  to  generate 
power  for  driving  the  blowers  and  other  purposes.  The  gas  has  to  be 
carefully  purified  from  dust  before  delivery  to  the  gas  engine. 

The  efficiency  of  the  internal-combustion  engine  is  much  greater 
than  that  of  the  steam  engine ;  thus  the  use  of  producer  gas  in  gas 
engines  is  the  most  efficient  method  of  converting  the  energy  of 
coal  into  power.  But  this  high  energy  efficiency  is  largely  offset 
by  the  greater  cost  of  installation  and  maintenance,  and  by  lack  of 
"  overload  "  capacity  of  the  engine.  Thus  with  the  exception  of 
conditions  of  unusual  constancy  of  load,  or  of  very  high  cost  of  fuel, 
the  steam  plant  is  the  cheapest  method  of  developing  power. 

To  secure  high  temperatures  by  gas  combustion,  preheating  of 
both  gas  and  air  before  they  enter  the  combustion  chamber  is  neces- 
sary. This  avoids  the  cooling  effect  they  otherwise  exert,  and  is 
most  economically  done  by  recovering  the  waste  sensible  heat  in 
the  reaction  products,  by  means  of  the  Siemens  regenerative  furnace, 
which  is  shown  in  its  simplest  form  in  Fig.  23.  The  material  to  be 
heated  is  placed  on  the  furnace  hearth  (A).  Four  passages  (B,  C, 
D,  and  E),  filled  with  loosely  piled  fire-brick  are  called  the  "  checker 
work."  On  their  way  to  the  chimney,  the  hot  gases  from  the  furnace 
pass  through  and  heat  two  checker  works,  e.g.  (B)  and  (C).  When 
they  are  sufficiently  heated,  the  flow  of  furnace  gases  is  turned  into 
(D)  and  (E),  through  which  they  pass  to  the  chimney.  Then  fuel  gas 
is  conducted  through  the  hot  passage  (B),  to  the  furnace  (A),  where 
it  mixes  with  air  which  has  been  heated  by  passing  through  (C). 
The  temperature  of  (A)  is  thus  much  higher  than  if  the  air  and  gas 


44 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


arrived  at  (A)  cold.  While  (B)  and  (C)  are  being  thus  cooled,  (D) 
and  (E)  are  heated  by  the  waste  gases,  and  after  a  time  the  dampers 
are  turned,  the  gas  made  to  pass  through  (E),  and  the  air  through 
(D),  while  the  combustion  products  pass  through  (B)  and  (C)  to  the 
chimney.  Hence  the  process  is  an  alternating  one,  the  checker  works 


FIG.  23. 


on  one  side  being  heated,  while  those  on  the  other  are  giving  up  their 
heat  to  the  gas  and  air  respectively.  The  interstices  between  the 
bricks  of  the  checker  work  often  become  clogged  with  ashes  and  soot. 
Recuperative  heating  involves  the  counter  current  flow  of  the  hot 
combustion  gases  through  or  around  flues,  on  the  other  side  of  which 
the  cold  gas  and  air  pass  to  the  furnace.  This  method  has  the  disad- 
vantage of  low  heat  conductivity  of  the  flue  walls,  but  avoids  all  in- 
termixture of  the  in-coming  and  out-going  gases.  The  flow  of  the 
gases  through  the  recuperator  is  continuous  and  there  is  no  periodic 
changing  of  valves  as  in  the  other  system. 

An  average  composition  of  various  fuel  gases  is  as  follows :  — 


H2 

CEU 

C2H6 

CO 

C02 

N2 

02 

Natural  gas  (Ohio)  *  .  . 
Coal  gasf  
Water  gasf 

2.3 

49.8 
508 

92.6 
29.5 
02 

0.3 
3.2 

0.5 
8.5 
409 

0.3 
1.6 
34 

3.5 
3.2 
35 

0.3 
0.4 
09 

Producer  gas  (coal)  f  .  . 

10.4 

6.3 

— 

17.6 

7.3 

58.1 

0.7 

When  burned  with  20  per  cent  excess  of  air,  and  assuming  that 
the  escaping  gases  have  a  temperature  of  500°  F.,  1000  cubic  feet 

*  Gas  and  Fuel  Analysis  for  Engineers,  A.  H.  Gill. 

t  Industrial  Chemistry,  Rogers  and  Aubert,  2d  ed.,  p.  404. 


FUELS  45 

of  gas  will  evaporate  the  following  number  of  pounds  of  water,  at 
from  60°  F.  to  212°  F. :  - 

Natural  gas 893  pounds  * 

Coal  gas 591  pounds 

Water  gas "    .     .     .  262  pounds 

Producer  gas 115  pounds 


REFERENCES 

Liquid  Fuel.     B.  H.  Thwaite,  London,  1887.     (Spon.) 

Chemical  Technology.     Groves  and  Thorp.     Vol.  1,  Fuel,  by  Mills  and 

Rowan,  Phila.,  1889.     (Blakiston.) 
Feuerungsanlagen.     F.  Fischer,  Karlsruhe,  1889. 
Liquid  Fuel.     E.  A.  B.  Hodgetts,  London,  1890.     (Spon.) 
Die  Feuerung  mit  flussigem  Brennmaterialien.     I.  Lew,  1890. 
Fuels.     H.  J.  Phillips,  London,  1891. 
Fuels.     C.  W.  Williams  and  D.  K.  Clark,  London,  1891. 
Die  Chemie  der  Steinkohle.     F.  Muck,  Leipzig,  1891.     (W.  Engelmann.) 
Die  Gasfeuerungen  fur  metallurgische  Zwecke.      A.   Ledebur,   Leipzig, 

1891. 

Taschenbuch  fur  Feuerung  stechniker.  F.  Fischer,  Stuttgart,  1893.  (Enke.) 
Contribution  a  1'etude  des  combustibles.     P.  Mahler,  Paris,  1893. 
Die  chemische  Technologic  der  Brennstoffe.     F.  Fischer,  Braunschweig, 

1896. 
A  Treatise  on  the  Manufacture  of  Coke  and  the  Saving  of  By-Products. 

John  Fulton,  Scranton,  Pa.,  1895. 

Mineral  Industry,  1895,  215,  W.  H.  Blauvelt.     (By-Product  Coke  Ovens.) 
Grundlagen     der     Koks-Chemie.      Oscar     Simmersbach,    Berlin,    1895. 

(J.  Springer.) 
The  Calorific  Power  of  Fuels.     Herman  Poole,  New  York,  1898.     (Wiley 

Sons.) 

Gas  and  Fuel  Analysis  for  Engineers.     A.  H.  Gill,  New  York,  3d  ed.,  1902. 
Modern  Power  Gas  Producer  Practice.     H.  Allen,  1908. 
Kraftgas.     Dr.  F.  Fischer,  Leipzig,  1911.     (Otto  Spamer.) 
Oil  Fuel.     S.  H.  North  and  Ed.  Butler,  2d  ed.,  London,  1911. 

*  Orton,  Geology  of  Ohio,  Vol.  VI,  p.  544. 


WATER 

Water  for  industrial  use  is  chiefly  obtained  from :  — 

1.  Surface  waters,  consisting  of, 
(a)  Flowing  waters  (streams). 
(6)  Still  waters  (ponds,  lakes). 

2.  Ground  waters,  furnished  by, 

(a)  Springs. 

(b)  Shallow   wells    (usually   penetrating    but    one    geological 

stratum). 

(c)  Deep  wells  (passing  through  several  geological  strata). 
Sea  water,  aside  from  some  use  for  condensers  and  for  supply  to 

marine  boilers,  finds  but  little  direct  use.  Rain  water  collected  from 
clean  roofs  or  other  surfaces  furnishes  excellent  soft  water  in  limited 
amount,  but  little  is  so  obtained  industrially. 

The  impurities  contained  in  water  may  be  derived  from  the  ground 
with  which  it  has  been  in  contact,  or  by  contamination  with  sewage 
or  factory  wastes.  In  general  the  impurities  in  water  constitute  four 
classes :  — 

I.  Dissolved  gases,  such  as  oxygen,  carbon  dioxide,  hydrogen 
sulphide,  etc. 

II.  Soluble   crystalloids,    consisting   of    definite   chemical    com- 

pounds which   cannot   be   removed   by  sedimentation   or 
filtration. 

III.  Soluble  colloids,  consisting  of  material  of  very  high  molecu- 

lar weight  which  will  not  settle  or  separate,  and  can  be 
filtered  only  through  semi-permeable  membranes. 

IV.  Suspended  matter  which  will  settle  or  can  be  filtered. 

I.  Dissolved  gases  may  comprise  two  groups :  (a),  those  whose 
solubility  diminishes  sufficiently  with  increase  of  temperature  in  the 
solution,  and  which  may  thus  be  removed  by  merely  heating  the  water 
in  open  heaters,  or  in  closed  vessels  with  the  aid  of  vacuum; 
(b)  those  requiring  chemical  treatment.  Acid  gases  may  be  neu- 
tralized (with  calcium  hydroxide  or  sodium  carbonate),  resulting  in 
precipitation,  or  not,  according  to  individual  circumstances.  Oxygen 
may  be  removed  by  passing  the  water  over  metallic  iron,  which 
is  readily  oxidized  to  the  ferric  state  and  precipitated,  owing  to 
hydrolysis. 

46 


WATER  47 

II.  The  soluble  crystalloids  include  most  of  the  impurities  occur- 
ring in  natural  waters,  and  their  removal  generally  involves  precipi- 
tation by  chemical  treatment.     The  presence  of  these  substances 
in  greater  or  less  amounts  imparts  to  the  water  those  properties  which 
render  it  hard,  soft,  saline,  or  alkaline.     Some  of  these  substances  may 
be  partially  or  wholly  removed  by  merely  heating  the  water.     Here 
two  groups  are  distinguished :    (a)  those  which  evolve  a  gas  at  higher 
temperatures  and  form  insoluble  bodies ;    (6)  those  whose  solubility 
decreases  as  the  temperature  increases  in  the  solution ;  thus  hydrated 
salts  in  solution  lose  water  of  hydration  as  the  temperature  rises  and 
pass  into  less  hydrated  and  less  soluble  forms. 

The  more  common  soluble  crystalloids  are  the  bicarbonates,  sul- 
phates, and  chlorides  of  calcium  and  magnesium ;  sodium  chloride, 
sulphate,  and  carbonate ;  iron  salts ;  and  silica.  These  are  the  sub- 
stances which  cause  the  most  difficulty  in  technical  work,  and  espe- 
cially when  the  water  is  used  in  steam  boilers. 

Hard  water  contains  salts  of  calcium,  magnesium,  or  iron,  and  is 
defined  as  one  which  precipitates  soap  from  solution.  Thus  hardness 
is  determined  by  titration  with  a  standard  soap  solution.  Tem- 
porary hardness  is  due  to  the  presence  of  bicarbonates  of  iron  and  the 
alkaline  earth  metals ;  the  neutral  carbonates  are  insoluble  but  dis- 
solve in  water  containing  free  carbon  dioxide,  forming  CaH^  (003)2, 
MgH2(CO3)2,  etc.  Permanent  hardness  is  due  to  the  presence  of 
soluble  neutral  sulphates  and  chlorides  of  calcium  and  magnesium. 

Soft  water  usually  contains  very  little  mineral  matter.  Rain 
water  as  it  falls  is  very  soft,  and  if  collected  from  clean  surfaces  is 
suitable  for  most  purposes.  Natural  waters  collected  from  ground 
containing  little  calcium  or  magnesium  in  soluble  form  is  fairly  soft 
as  a  rule;  but  if  the  water  has  percolated  through  soil  containing 
peat  or  decaying  vegetable  matter,  it  is  often  discolored  by  dissolved 
organic  matter,  and  may  contain  organic  acids  which  cause  corrosion 
of  iron  or  other  metals. 

Saline  and  alkaline  waters  contain  the  sulphates,  carbonates,  or 
halogen  salts  of  the  alkali  metals,  in  rather  large  amounts.  Sea  water 
and  many  ground  waters  (springs,  wells)  are  characteristically  saline 
(mineral  waters).  Alkaline  waters  are  high  in  carbonates  and  sul- 
phates ;  as,  e.g.  the  "  alkali  "  waters  of  the  western  states. 

III.  Colloidal  substances  have  very  large  molecular  weight,  and 
are  characterized    by  the  tendency  to  adsorb  or  condense   on  the 
boundary  surfaces  of  precipitated  matter,  if  these  surfaces  are  rela- 
tively  large.     Thus   to   remove   colloidal   matter   from   solution,    a 


48  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

flocculent  or  finely  divided  amorphous  precipitate  may  be  produced 
in  the  water,  which  adsorbs  the  colloidal  matter  and  attaches  it  to  the 
precipitate.  Crystalline  precipitates  have  relatively  small  surfaces, 
and  do  not  serve  well  for  removing  colloidal  matter. 

Colloidal  substances  in  water  form  two  groups :  (a)  Suspension 
colloids,  consisting  of  small  particles  of  suspended  solid  matter,  which 
may  be  easily  coagulated  and  precipitated  by  adding  some  electro- 
lite.  (6)  Emulsion  colloids  consisting  of  minute  particles  of  in- 
soluble matter  probably  liquid,  suspended  in  the  water,  e.g.  emulsified 
oils,  gelatine,  gums,  and  certain  hydrated  compounds  mostly  of  complex 
structure,  such  as  some  varieties  of  clays,  tannic  acids,  humus  bodies, 
etc.  Emulsion  colloids  are  usually  difficult  to  coagulate,  and  only 
when  much  precipitating  agent  is  added,  can  it  be  done.  Thus  if 
emulsion  colloids  predominate  in  a  water,  purification  may  be  imprac- 
ticable, owing  to  the  large  quantity  of  precipitant  needed ;  but  these 
colloids  can  often  be  adsorbed  on  the  surfaces  of  suitable  materials, 
such  as  alumina,  iron  hydroxide,  charcoal  or  bone-char. 

Some  substances  present  in  natural  waters  may  impart  to  it 
corrosive  properties,  making  its  use  objectionable  for  industrial 
purposes.  Dissolved  oxygen  and  carbon  dioxide,  hydrogen  sulphide, 
free  acids,  either  mineral  or  organic,  and  easily  hydrolized  salts,  as 
MgCU  and  FeSO4,  are  very  liable  to  cause  corrosion  or  "  pitting  " 
in  a  boiler.  Some  of  these  may  be  derived  from  factory  wastes,  or 
from  swamps  and  peat  bogs,  or  from  mine  sumps  and  drainage  from 
culm  or  refuse  dumps. 

The  purification  of  water  for  industrial  use  consists  in  the  partial 
or  complete  removal  of  the  objectionable  substances  suspended  or 
dissolved  in  it.  This  is  often  difficult,  owing  to  the  nature  of  the 
impurities ;  the  size  of  the  plant  required  for  large  works  is  also  an 
item  of  concern.  The  quality  of  the  water  available  should  be  con- 
sidered in  locating  the  works. 

Water  containing  suspended  matter  only  may  be  purified  by  sedi- 
mentation, followed  by  sand  filtration;  but  this  is  often  combined 
with  chemical  treatment,  by  which  a  precipitate  is  formed  in  the  water. 
This  precipitate  acts  mechanically  to  entangle  the  suspended  matter ; 
and  it  also  acts  as  an  adsorption  agent  on  emulsion  colloids,  such  as 
dissolved  organic  coloring  matter,  grease  or  oils,  glutinous  substances, 
and  many  kinds  of  factory  wastes.  Aeration  by  spraying  into  the 
air,  or  by  trickling  in  thin  films  over  large  surfaces,  accelerates  the 
escape  of  carbon  dioxide,  or  hydrogen  sulphide,  while  absorption  of 
oxygen  aids  precipitation  of  iron  from  solution.  Bacteria  and  other 


WATER  49 

organisms  are  frequently  destroyed  in  sewage  effluents,  and  in  mu- 
nicipal supplies,  by  treatment  with  hypochlorites,  ozone,  or  copper 
sulphate.  Generally  the  raw  water  is  mixed  with  some  soluble  salt, 
such  as  aluminum  or  ferrous  sulphate,  which  is  precipitated  as  alumi- 
num or  iron  hydroxide  by  the  action  of  the  alkaline  substances  in  the 
water,  or  added  to  it  later.  This  gelatinous  precipitate  encloses 
suspended  matter,  and  combines  with  soluble  organic  coloring  matter 
by  adsorption;  by  filtration  on  sand  filters  (p.  19)  it  is  removed, 
carrying  with  it  the  impurities.  But  this  increases  the  soluble  im- 
purity by  the  alkaline  sulphates  left  in  the  water.  Sulphuric  acid 
and  iron  sulphate  are  removed  from  Allegheny  River  water  for  the 
Pittsburgh  city  supply,  by  adding  calcium  chloride.*  The  calcium 
sulphate  precipitate  aids  in  removing  the  suspended  silt  and  coloring 
matter. 

Water  for  boiler  supply  is  generally  treated  to  reduce  the  hard- 
ness or  to  neutralize  its  corrosive  properties ;  the  operation  is  called 
"  softening.'*  Temporary  hardness  is  removed  by  some  of  the  fol- 
lowing methods :  — 

1.  Boiling  the  water,  usually  in  "feed-water  heaters,"  to  decom- 
pose the  bicarbonates :  — 

CaH2(CO3)2  =  CaCO3  +  H2O  +  CO2. 

Feed-water  heaters  are  heated  by  exhaust  steam,  or  waste  flue-gases, 
and  may  be  "  open,"  when  working  under  atmospheric  pressure,  or 
"  closed "  if  under  internal  pressure  (as  economizers),  or  under 
vacuum.  Open  heaters  permit  the  ready  escape  of  dissolved  gases 
and  decomposition  of  bicarbonates,  with  precipitation  of  iron,  cal- 
cium, and  magnesium,  but  for  complete  separation  of  the  alkaline 
earths,  a  small  amount  of  sodium  carbonate  must  be  added  to  the 
water  in  the  heater,  to  decompose  any  permanent  hardness.  Closed 
heaters  working  under  pressure  (economizers)  afford  less  complete 
separation  of  hardness,  since  the  gases  cannot  readily  escape.  In 
vacuum  heaters  the  gases  are  removed,  and  the  water  is  purified. 

Heaters  employing  waste  flue  gases  are  known  as  "  economizers," 
the  water  being  heated  in  tubes  set  in  the  furnace  flue.  The  condi- 
tions are  essentially  those  prevailing  in  the  boiler  and  the  scale  de- 
posits inside  of  the  tubes,  which  need  to  be  frequently  cleaned. 

2.  Treatment  with  calcium  hydroxide   ("  milk  of  lime  ") :  — 

CaH2(C03)2  +  Ca(OH)2  =  2  CaCO3  +  2  H2O. 

*  Hoffmann,  J.  Ind.  Eng.  Chem.,  VI  (1914)  p.  52. 
E 


50  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

The  clear  calcium  hydroxide  solution  obtained  by  letting  the  undis- 
solved  lime  settle  is  preferable  for  this,  but  frequently  unsettled 
"  milk  of  lime "  is  used.  The  required  amount  of  quicklime  is 
slaked  in  a  little  water,  and  the  "  milk  "  thoroughly  mixed  with  the 
water  to  be  purified.  This  is  Clarke's  process.  The  sludge  of  cal- 
cium carbonate  is  removed  by  settling  in  suitable  tanks,  or  by  a 
filter-press. 

3.  Treatment  with  sodium  carbonate  (soda-ash) :  — 

CaH2(CO3)2  +  Na2CO3  =  CaCO3  +  2  NaHCO3. 

The  permanent  hardness  is  less  easily  remedied,  for  in  these  cases 
treatment  of  the  water  leaves  some  substance  more  or  less  deleterious 
in  solution :  — 

1.  CaSO4  +  Na2CO3  =  CaCO3  +  Na2SO4. 

2.  CaS04  +  Ba(OH)2  =  BaSO4  +  Ca(OH)2. 

3.  CaCl2  +  Na2C2O4  =  2  NaCl  +  CaC2O4. 

Much  care  is  necessary  to  avoid  an  excess  of  the  chemical  added.* 

When  natural  water  containing  soluble  impurities  is  used  in  a 
boiler,  a  more  or  less  coherent  deposit,  called  boiler  scale,  forms  on 
the  plates  and  tubes.  This  is  chiefly  composed  of  carbonate  and  sul- 
phate of  calcium ;  but  in  some  cases  magnesium  hydroxide  and  sul- 
phate, iron  hydroxide  or  oxide,  silica  and  organic  matter,  are  present. 
The  decomposition  of  bicarbonates  of  calcium  and  magnesium  by 
heat,  as  above  indicated,  also  takes  place  in  the  boiler.  Calcium  car- 
bonate alone  forms  a  porous,  non-adherent  scale  or  sludge,  which  is 
largely  removed  by  "  blowing  off  "  or  washing  out  the  boiler.  Cal- 
cium sulphate  is  rendered  less  soluble  by  the  heat  and  pressure  within 
the  boiler,  and  is  deposited  as  a  hard,  compact  scale,  adhering  firmly 
to  the  plates  and  tubes.  Magnesium  sulphate,  if  present,  is  deposited 
as  monohydrated  salt  (MgSO4 '  H2O),  and  is  strongly  adherent. 

Scale  formation  is  very  detrimental ;  being  a  poor  conductor  of 
heat,  the  evaporative  capacity  of  the  boiler  is  reduced  and  much 

*  Besides  the  methods  given  above,  many  other  substances  have  been  proposed, 
and  are  used  to  some  extent,  usually  within  the  boiler  itself,  for  water  purification. 
Among  these  are  sodium  hydroxide,  phosphate,  aluminate,  fluoride,  oxalate,  silicate, 
and  bichromate ;  also  barium  hydroxide  and  aluminate.  But  in  general  these  are 
too  expensive  for  large  works. 

1.  MgH2(CO3)2  +  2  NaOH  =  MgCOs  +  Na2CO3  +  2  H2O. 

2.  CaH2(CO3)2  +  Na2Cr2O7  =  CaCrO4  +  Na2CrO4  +  2  CO2  +  H2O. 

3.  MgSO*  +  Na2Cr207  =  MgCKX  +  Na2SC>4  +  CrO3. 
J.  Am.  Chem.  Soc.  1899,  655.     Eng.  Min.  Jour.  LX,  220. 


WATER  51 

more  fuel  is  consumed.  The  scale  separates  the  water  from  the  boiler 
plates  and  tubes,  which  thus  are  overheated  and  rapidly  burn  out. 
The  tubes  also  become  clogged  and  their  efficiency  is  much  impaired. 
Magnesium  chloride  is  especially  troublesome,  for  it  not  only 
forms  scale,  but  causes  rapid  corrosion  of  the  iron,  possibly  thus :  — 

MgCl2  +  Fe  +  2  H2O  =  Mg(OH)2  +  FeCl2  +  H2. 

Dissolved  oxygen  and  carbon  dioxide,  and  hydrogen  sulphide,  are 
strongly  corroding,  the  latter  probably  because  of  oxidation  to  sul- 
phuric acid.  Manganese  sulphide  in  the  boiler  plates  assists  depo- 
larization of  the  hydrogen ;  it  may  also  be  oxidized  and  hydrolized 
to  form  sulphuric  acid,  and  thus  accelerate  corrosion. 

As  a  rule  the  water  should  be  treated  before  it  goes  into  the  boiler, 
but  if  the  scale-forming  impurity  does  not  exceed  170  parts  per  mil- 
lion, the  purification  may  be  done  in  the  boiler  itself,  followed  by  a 
daily  "blowing  off."  A  good  circulation  of  water  in  the  boiler  tends 
to  keep  the  precipitated  matter  loose  so  it  may  be  easily  blown  out. 

In  some  cases  scaling  may  be  prevented  by  introducing  colloidal 
substances  into  the  boiler ;  possibly  the  particles  of  incrusting  matter 
become  coated  with  a  thin  film  of  the  colloid  by  adsorption.  Coales- 
cence of  the  particles  of  the  crystalloids  is  thus  prevented  and  they 
form  a  loose  sludge,  or  are  kept  in  suspension  in  the  water,  until  re- 
moved by  "  blowing  off,"  or  wrashing  out  the  boiler.  The  use  of 
kerosene,  of  tannins,  and  of  other  organic  substances  in  the  boiler  is 
based  upon  this  action. 

Many  proprietary  "  anti-scale  "  preparations  are  sold,  some  of 
which  are  of  no  particular  value.  These  are  generally  intended  for 
use  inside  of  the  boiler,  and  may  act  by  direct  precipitation  of  mineral 
matter,  or  by  preventing  adhesion  to  the  boiler  plates.  They  often 
contain  soda-ash,  caustic  soda,  sodium  silicate  or  phosphate,  barium 
hydroxide,  tannins  or  vegetable  extracts,  or  petroleum  products. 

Saline  or  alkaline  waters,  or  those  whose  content  of  alkali  sulphates 
and  chlorides  has  been  artificially  raised  by  purification  methods 
as  above,  may  give  trouble  in  steam  boilers  by  causing  "priming," 
i.e.  the  passage  of  water  particles,  mixed  with  the  steam,  from  the 
boiler.  Priming  is  associated  with  foaming,  resulting  from  much 
dissolved  matter,  or  due  to  finely  divided  suspended  particles.  When 
water  contains  a  great  number  of  suspended  fine  solid  particles,  each 
serves  to  release  steam  bubbles  in  its  immediate  vicinity,  and  this 
increases  the  space  occupied  by  the  water  in  the  boiler,  i.e.  foaming  is 


52 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


caused.*  The  presence  of  large  amounts  of  alkaline  chlorides  and 
sulphates,  along  with  much  calcium  or  magnesium  sulphate,  may  ren- 
der a  natural  water  useless  for  steam  raising,  since  it  will  foam  after 
chemical  treatment.  No  satisfactory  method  of  purifying  such  waters 
has  yet  been  proposed.  Frequent  blowing  off  of  the  boiler  is  the  only 
preventive  of  foaming.  In  locomotives  foaming  may  occur  when 
the  dissolved  salts  amount  to  1700  parts  per  million ;  but  stationary 
boilers  will  permit  four  times  as  much. 

Grading  of  natural  water  for  steam  raising  is  often  difficult,  owing 
to  the  local  conditions  in  the  region  where  the  water  is  to  be  used.  A 
water  containing  250  parts  per  million  would  be  considered  poor  in 
some  parts  of  New  England,  but  would  rank  as  good  in  Dakota  or 
Iowa.  A  classification  proposed  f  for  locomotive  supply  is  shown 
below :  — 


INCRUSTING  OR  CORRODING 
CONSTITUENTS. 
PARTS  PER  MILLION. 

FOAMING  CONSTITUENTS. 
PARTS  PER  MILLION. 

More  than 

Not  more  than 

More  than 

Not  more  than 

Good        .     .     .    *    . 

90 
200 
430 
680 

90 
200 
430 
680 

70 
150 

250 
400 

150 
250 

400 

Fair     .     .     .     .     .     . 
Poor                    .     .  '   . 

Bad     

Very  bad       .     .     ,     ,, 

The  character  of  the  water  available  is  very  important  in  some 
manufacturing  processes.  Hard  water  is  objectionable  for  laundries, 
bleacheries,  and  soap  works,  since  the  insoluble  lime  soaps  are  pre- 
cipitated, causing  loss  of  considerable  soap,  and  injury  to  the  goods, 
owing  to  the  insoluble  soaps  adhering  to  them. 

i 

The  permutite  process  t  for  water  softening  is  used  somewhat  in  dye 
works  and  bleacheries.  Permutite  is  an  artificial  zeolite  (hydrated  silicate 
of  sodium  and  aluminum)  made  by  fusing  together  feldspar,  kaolin,  and 
alkali  carbonates,  and  lixiviating  the  pulverized  mass  with  hot  water. 
The  composition  is  given  as  2  SiO2-Al2O3-Na2O-6  H20,  and  the  substance 
is  practically  insoluble  in  water.  Upon  contact  with  water  containing 
bicarbonates  or  sulphates  of  calcium  or  magnesium,  or  iron  or  manganese 

*  Railroad  Gazette,  Oct.  12,  1900.    C.  H.  Koyl. 

fProc.  Am.  Ry.  Eng.  and  Maintenance  of  Way  Assoc.  V  (1904),  595;  IX 
(1908),  134. 

I  Textile  World  Record,  Nov.  1912. 


WATER  53 

salts,  an  interchange  takes  place  between  the  sodium  of  the  permutite 
and  the  metal  of  the  dissolved  salts  ;  thus  :  — 

Na2O  •  A1203  •  2  SiO2  •  6  H2O  +  CaH2(CO3)2  = 

CaO  •  A12O3  •  2  Si02  •  6  H20  +  2  NaHCO3. 
NasO  •  A1203  •  2  Si02  -  6  H2O  +  MgSO4  =  MgO  •  A1203  -  2  SiO2 . 6  H2O  +  Na2SO4. 

Thus  by  simple  nitration  through  a  layer  of  granular  sodium  permutite, 
a  hard  water  can  be  softened.  When  the  permutite  becomes  inactive 
through  deposition  of  alkaline  earth  metal  and  removal  of  the  sodium,  the 
material  can  be  regenerated  in  situ,  by  washing  for  8  to  10  hours  with  a 
10  per  cent  sodium  chloride  solution  ;  thus  :  — 

CaO  •  A12O3  •  2  Si02  •  6  H2O  +  2  NaCl  =  Na^O  •  A12O3  •  2  SiO2  -  6  H2O  +  CaCl2. 

Hard  waters  may  cause  unevenness  of  color  deposition  in  dyeing ; 
they  also  lower  the  quantity  of  extract  matter  taken  up  from  malt 
in  brewing  and  distilleries.  Iron  in  any  form  is  very  bad  for  dye- 
ing, tanning,  paper  making,  bleacheries,  laundries,  and  for  brew- 
ing; it  causes  dark  color  in  the  material.  Moderate  hardness  due 
to  sulphates  is  of  advantage  in  paper  making;  for  tanning  sole 
leather,  owing  to  its  swelling  effect  on  the  hides,  and  for  brewing 
pale  beers,  since  it  decreases  the  extraction  of  coloring  matters  and 
protein  substances  from  the  malt.  Chlorides  are  injurious  in  nearly 
all  cases  where  the  water  comes  in  direct  contact  with  the  material, 
as  in  foods,  in  the  brewing  and  distilling  industries,  in  sugar  mak- 
ing, and  in  tanning. 

Suspended  matter,  either  of  mineral  or  organic  nature,  and  dis- 
solved organic  coloring  substances,  may  cause  discoloration,  or  spots 
in  goods  with  which  they  come  in  contact :  thus  paper-mills,  dye  works, 
bleacheries,  and  starch  factories  require  a  perfectly  clear  and  color- 
less water.  The  presence  of  organic  dirt  may  cause  decomposition 
or  putrefactive  changes  in  food  products,  in  the  fermentation  indus- 
tries, in  starch  and  sugar  making. 

REFERENCES 

Die   Chemische   Technologic   des  Wassers.     F.   Fischer,   Braunschweig, 

1880. 

Die  Verhutung  un'd  Beseitigung  des  Kesselsteins.  W.  Storck,  Halle,  1881. 
A  Treatise  on  Steam  Boiler  Incrustations.  C.  T.  Davis,  Washington, 

1884. 

Water  Supply.    William  R.  Nichols,  1886. 
Report  on  Boiler  Waters  of  the  C.  B.  &  Q.  R.R.     W.  L.  Brown,  Chicago, 

1888. 

Die  Verunreinigung  der  Gewasser.     K.  W.  Jurisch,  Berlin,  1890. 
Das  Wasser.     F.  Fischer,  Berlin,  1891.     (J.  Springer.) 
Das  Reinigen  von  Speisewasser  fur  Dampfkessel.     A.  Rossel,  Winterthur. 

1891. 


54  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

L'Eau  dans  1'Industrie.     P.  Guichard,  Paris,  1894.     (Bailliere.) 

Report  of  the  Filtration  Commission  of  the  City  of  Pittsburg,  1899. 

American  Machinist,  22  (1899).  A.  A.  Gary.  (Use  of  Boiler  Com- 
pounds.) 

L'Eau  dans  1'Industrie.     De  la  Coux,  Paris,  1900. 

Boiler-Waters.     Wm.  W.  Christie,  New  York,  1906.     (Van  Nostrand.) 

Clean  Water  and  How  to  Get  It.     Allen  Hazen,  New  York,  1907. 

Stream  Pollution  in  Potomac  River  Basin.  H.  N.  Parker.  U.  S.  Geol. 
Survey,  Water  Supply  Paper,  No.  192  (1907). 

Disinfection  of  Sewage  and  Sewage  Filter  Effluents.  E.  B.  Phelps. 
U.  S.  Geol.  Survey,  Water  Supply  Paper,  No.  229  (1909). 

Proc.  Western  Railway  Club,  1903,  241. 

Eng.  Min.  Jour.  1895,  220.     F.  Wyatt.     1899,  443.     J.  H.  Parsons. 

J.  Soc.  Chem.  Ind.  1884,  51.  J.  H.  Porter.  1886,  267.  Macnab  and 
Beckett.  416.  A.  Steiger.  1887,  178.  V.  C.  Driffield.  1888, 795. 
A.H.Allen.  1891,511.  Archbutt  and  Deeley. 

Eng.  News.  60  (1908),  355.     H.  Stabler. 


SULPHUR 

Most  of  the  sulphur  used  in  the  industries  is  derived  from  the 
native  mineral,  which  is  found  in  many  places,  but  usually  in  volcanic 
regions.  It  is  always  impure,  being  mixed  with  gypsum,  aragonite, 
clay,  or  other  matter,  in  the  interstices  of  which  the  sulphur  is  de- 
posited. The  formation  of  sulphur  beds  may  have  occurred  by  the 
reaction  of  gases,  such  as  hydrogen  sulphide  and  sulphur  dioxide, 
with  each  other  or  with  oxygen ;  or  by  the  decomposition  of  metallic 
sulphides  through  the  agency  of  heat ;  or  by  the  reduction  of  sulphates, 
especially  of  calcium  sulphate,  which  has  probably  caused  the  for- 
mation of  some  stratified  deposits. 

The  first  is  probably  the  most  frequent  mode  of  deposition,  and 
may  be  observed  at  the  present  time  in  many  volcanic  districts  where 
hydrogen  sulphide  and  sulphur  dioxide  are  escaping.  The  reactions 
are  the  following :  — 

SO2  +  2H2S  =  2  H2O  +  3S; 

H2S  +  O  =  H2O  +  S ; 
H2S  +  3  O  =  H2O  +  S02. 

The  largest  part  of  the  world's  supply  of  sulphur  comes  from 
Sicily,  but  some  is  obtained  in  Japan,  Italy,  Greece,  and  in  the 
United  States,  particularly  in  Louisiana,  in  Wyoming,  in  Utah,  and 
near  Humboldt,  Nevada.  The  Louisiana  deposit  is  now  yielding 
a  sufficient  supply  for  our  domestic  consumption  and  shipment 
abroad  has  been  introduced. 

In  Sicily  it  is  disseminated  through  the  matrix,  sometimes  in 
considerable  masses  of  nearly  pure  sulphur,  but  usually  in  fine  seams 
or  grains.  The  methods  of  obtaining  it  are  very  crude  and  wasteful. 
The  mines  are  for  the  most  part  open  pits,  ranging  from  200  to  500 
feet  in  depth,  and  the  ore  is  carried  to  the  surface  in  baskets  or  sacks 
by  laborers,  who  ascend  by  inclined  paths  on  the  walls  of  the  pit. 
In  some  of  the  better  mines,  however,  hoisting  machinery  is  now  used, 
but  only  after  overcoming  the  determined  opposition  of  the  laborers. 
The  ore  is  generally  refined  in  a  very  simple  manner,  the  process  being 
carried  on  in  kilns  called  "  calceroni"  As  usually  constructed,  these 
are  shallow  pits,  about  30  feet  in  diameter,  with  walls  about  10  feet 
high,  made  tight  with  mortar.  They  are  generally  built  on  a  hill-side, 
and  the  sloping  bottom  is  beaten  smooth.  The  ore  is  arranged  in 
the  calcerone  so  as  to  leave  a  few  vertical  draught  holes  from  top  to 

55 


56  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

bottom  of  the  heap,  which  is  fired  by  dropping  burning  brush  or  straw 
into  these  openings.  The  sulphur,  forming  from  25  to  40  per  cent  of 
the  ore,  burns  freely,  and  when  the  heap  is  well  on  fire,  the  draught 
holes  are  closed,  the  calcerone  covered  with  spent  ore,  and  the  whole 
left  for  several  days.  The  heat  given  out  by  the  burning  of  part 
of  the  sulphur  is  sufficient  to  melt  the  remainder  from  the  gangue, 
and  it  collects  in  a  pool  near  a  tap-hole,  made  in  the  wall  at  the  lowest 
point.  At  intervals  of  a  few  hours,  the  melted  sulphur  is  drawn  off 
into  moulds.  If  the  temperature  rises  above  180°  C.,  there  is  a 
large  formation  of  plastic  sulphur,  which  will  not  flow  from  the  tap- 
hole.  To  burn  out  a  calcerone  requires  35  to  80  days,  depending  on 
its  size,  the  amount  of  gypsum  in  the  ore,  and  the  weather.  From  a 
quarter  to  a  third  of  the  sulphur  is  lost  as  sulphur  dioxide,  and  as 
this  damages  vegetation,  calcerone  burning  is  prohibited  during  the 
spring  and  summer  months. 

Of  recent  years  the  Gill  kiln,  paterned  after  the  Hoffmann  furnace 
(p.  185),  has  been  introduced.  This  uses  part  of  the  sulphur  as  fuel 
and  consists  of  four  to  six  chambers,  the  air  for  combustion  entering 
that  chamber  where  the  melting  has  just  been  finished.  The  air 
thus  warmed  enters  the  second  chamber,  where  combustion  is  at  its 
highest  point  and  the  sulphur  is  melted  out  of  the  ore ;  the  hot  gases 
pass  to  the  next  chamber,  filled  with  fresh  ore,  which  is  thus  heated 
to  the  fusion  point  of  the  sulphur  before  combustion  begins.  The 
waste  gases  finally  pass  to  the  chimney.  The  yield  of  sulphur  is 
considerably  better  than  by  the  calcerone  method. 

Processes  for  extraction  of  the  sulphur  by  means  of  carbon  disul- 
phide  or  other  solvents  have  proved  too  expensive  for  industrial 
use.  Extraction  with  superheated  steam*  yields  an  excellent  quality 
of  sulphur  without  formation  of  sulphur  dioxide,  and  is  used  in  this 
country  and  Japan  to  some  extent. 

In  Wyoming,  sulphur  occurs  as  irregular  deposits  or  pockets  in 
limestone.  The  ore  is  broken  to  small  size,  loaded  into  steel  cars 
having  perforated  sides,  and  run  into  a  retort  where  steam  at  60  Ibs. 
pressure  is  admitted ;  the  sulphur  melts,  flows  to  the  bottom  of  the 
retort,  leaving  the  gangue  rock  in  the  car. 

By  boiling  the  ore  in  a  concentrated  solution  of  calcium  chloride  f 
at  125°  C.,  the  sulphur  can  be  melted  from  the  gangue,  with  no  forma- 
tion of  sulphur  dioxide,  and  no  nuisance  is  caused.  This  has  been 
tried  in  Sicily,  but  is  not  in  general  use. 

*  J.  Soc.  Chem.  Ind.  1887,  439,  442 ;    1889,  696. 

t  Vincent,  Bull.  Soc.  Chim.  40,  528.     Am.  Chem.  Jour.  VI,  63. 


SULPHUR  57 

In  Louisiana,  sulphur  is  obtained  by  the  method  devised  by  Her- 
mann Frasch,*  which  has  been  very  successful.  Driven  wells  are 
sunk  into  the  deposit,  which  lies  at  a  depth  of  about  450  feet,  and  is 
about  100  feet  thick.  In  each  well  are  four  concentric  lines  of  pipe, 
ranging  in  diameter  from  10  inches  to  1  inch.  Superheated  water 
(165°  to  170°  C.)  is  forced  down  between  the  10-inch  and  6-inch  pipes, 
and  passing  into  the  crevices  of  the  sulphur-bearing  rock,  melts  the 
sulphur,  which  runs  into  the  sump  at  the  foot  of  the  well.  Through 
the  1-inch  pipe,  compressed  hot  air  is  forced  to  the  bottom  of  the  well, 
where  it  mixes  with  the  melted  sulphur,  forming  an  aerated  mass, 
which  the  water  and  air  pressure  cause  to  rise  through  the  4-inch  pipe, 
to  the  surface ;  the  mixture  of  melted  sulphur,  hot  water,  and  air  is 
discharged  into  large  open  vats  made  of  boards.  The  solidified  sul- 
phur goes  direct  to  market  without  further  refining,  and  is  of  better 
quality  than  that  from  Sicily,  which  it  has  practically  displaced  from 
the  American  market. 

A  small  part  of  the  sulphur  of  commerce  is  recovered  sulphur, 
chiefly  obtained  from  the  calcium  sulphide  waste  of  the  Leblanc 
soda  process  (p.  103  et  seq.),  and  from  the  residues  from  the  purifica- 
tion of  illuminating  gas  by  iron  oxide  (p.  321).  The  residues  con- 
taining 50  to  60  per  cent  of  free  sulphur  are  heated  in  a  retort  and  the 
sulphur  distilled  off.  It  seems  improbable  that  recovered  sulphur 
will  ever  become  much  of  a  factor  in  the  market. 

The  sulphur  obtained  by  the  above  described  processes  is  gen- 
erally pure  enough  for  manufacturing  and  agricultural  uses.  But  in 
a  few  industries,  a  refined  sulphur  is  needed.  This  is  produced  by 
distillation  from  an  iron  retort,  the  vapors  being  condensed  in  brick 
chambers.  If  the  temperature  of  the  chamber  is  not  above  110°  C., 
the  vapors  condense  at  once  to  a  fine  powder,  called  "  flowers  of 
sulphur  " ;  but  if  the  temperature  in  the  condensing  chamber  rises 
much  above  110°  C.,  the  vapors  condense  to  a  liquid,  which  is  drawn 
into  moulds  to  form  the  "  roll  brimstone  "  of  commerce. 

The  chief  uses  for  crude  sulphur  are:  for  combating  Oidium 
tuckeri,  a  fungus  causing  the  vine  disease  (this  disposes  of  a  large  part 
of  the  yearly  production) ;  for  making  sulphuric  acid ;  for  sulphurous 
acid  and  bisulphite  solutions  ;  for  carbon  di sulphide ;  and  for  making 
ultramarine.  Refined  sulphur  goes  mainly  for  gunpowder,  matches, 
and  for  vulcanizing  rubber. 

*  U.  S.  Pat.  Nos.  461429,  461430,  461431.  Mining  World,  1907,  1049. 
Eng.  Min.  J.  1907  (84),  1107.  Mineral  Resources  of  the  United  States,  1907, 
(Pt.  II),  674, 


58 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


Sulphur  melts  at  115°-120°  C.,  and  has  a  specific  gravity  of  1.98- 
2.04 ;  it  is  a  poor  conductor  of  heat  and  electricity,  dissolves  easily 
in  carbon  disulphide,  and  less  readily  in  chloroform,  benzol,  turpentine, 
and  other  oils. 

Sicily,  owing  to  its  favorable  situation  as  a  shipping  point,  the 
abundance  of  cheap  labor,  and  its  rich  deposits,  was  long  the  dominat- 
ing factor  in  the  sulphur  market.  But  recent  competition  with  the 
American  and  Japanese  production  of  sulphur  has  caused  the  closing 
of  many  of  the  mines,  and  those  which  have  continued  working  have 
met  with  large  losses.  Only  by  greatly  improving  their  methods  of 
mining  and  refining  the  ore  can  the  industry  be  restored  to  a  satis- 
factory condition.  At  the  present  time  the  American  sulphur  industry 
in  Louisiana  is  in  a  flourishing  condition. 


SULPHUR  DERIVATIVES 

Sulphur  dioxide  (SO2)  is  the  most  important  sulphur  compound 
and  is  made  on  a  large  scale  by  roasting  iron  pyrites  (p.  66)  for  the 

sulphuric  acid  manufacture :  for  pro- 
ducing smaller  quantities  of  sulphur 
dioxide  direct  combustion  of  brim- 
stone is  customary.  Brimstone  burn- 
ers may  be  simple  brick  ovens,  or 
long  iron  retorts,  in  which  the  sul- 
phur is  ignited  and  a  regulated 
supply  of  air  admitted  to  ensure 
complete  combustion.  Too  much 
heat  in  the  retort  may  cause  distil- 
lation of  sulphur  into  the  flues  and 
other  parts  of  the  apparatus.  Me- 
chanical sulphur  burners  afford  more 
uniform  combustion  and  high  con- 
centration of  the  sulphur  dioxide  gas. 
A  modern  type  is  the  Wise  sulphur  burner  (Fig.  24),  consisting  of  a 
cast-iron  bowl  (B),  with  an  agitator  (A)  whose  ploughs  dip  into  the 
melted  sulphur  (C)  in  the  bowl.  Air  enters  by  openings  (D)  in  the 
wall  just  above  the  surface  of  the  burning  sulphur.  In  the  annular 
trough  (E)  is  placed  brimstone,  which  is  melted  by  the  heat  of  the 
burner  itself,  and  flows  through  the  inlets  (F)  into  the  bowl,  replacing 
that  which  is  burned  to  sulphur  dioxide.  Above  the  sulphur  pot  is 
a  combustion  box  (G),  in  which  is  a  horizontal  baffle  plate  with  slots 


FIG.  24. 


SULPHUR  59 

at  each  end.  Opposite  each  slot  is  a  damper  in  the  end  of  the  com- 
bustion box,  to  admit  air  for  completing  the  combustion  of  any  sul- 
phur vapor.  Thus  sublimation  of  the  sulphur  is  avoided  and  the 
sulphur  dioxide  concentration  in  the  gas  is  high,  18  to  19  per  cent  by 
volume  being  claimed. 

The  Tromblee-Paull  burner  is  a  rotary,  horizontal  iron  cylinder,  8 
feet  long  and  3  feet  in  diameter,  having  conical  ends ;  it  makes  one  revo- 
lution in  two  minutes,  and  consumes  about  5500  Ibs.  of  sulphur  per 
day.  The  sulphur,  melted  by  the  heat  of  the  burner,  flows  into  the 
cylinder,  coating  the  interior  of  the  shell  in  consequence  of  the  rotation. 
Air  entering  through  suitable  dampers  in  one  end  of  the  cylinder  burns 
the  sulphur  on  the  inner  surface  of  the  shell,  and  the  gases  pass  into  a 
combustion  chamber  to  complete  the  burning  of  any  volatilized  sulphur. 

Much  sulphur  dioxide  is  produced  in  the  roasting  and  smelting 
of  copper  and  lead  ores  (p;  594  et  seq.)  and  recently  attention  has 
been  given  to  the  condensation  of  these  fumes  for  the  making  of  acid 
or  other  purposes,  but  chiefly  with  the  object  of  abating  the  nuisance 
and  damage  they  cause  in  the  surrounding  country. 

Pure  sulphur  dioxide  is  made  by  dissolving  the  crude  gas  from 
sulphur  burners  in  water  by  use  of  counter-current  washing  towers, 
and  recovering  it  from  the  solution  by  heating.  The  gas  is  dried, 
compressed  to  liquid,  and  put  on  the  market  in  steel  cylinders. 

Sulphur  dioxide  is  used  for  making  sulphuric  acid ;  for  the  acid 
sulphite  liquor  used  in  making  wood  pulp ;  for  preparing  sodium  bisul- 
phite as  a  bleaching  agent  for  wool,  hair,  straw,  and  other  tissues ; 
as  a  disinfectant  and  germicide ;  and  in  the  liquid  state  in  ice  machines. 

Substances  such  as  wool  and  straw,  when  bleached  by  exposure 
to  sulphur  dioxide  gas,  slowly  regain  their  original  color  on  exposure 
to  the  light.  The  coloring  matter  is  not  destroyed,  but  probably 
unites  with  the  sulphur  dioxide  to  form  a  colorless  compound,  which 
slowly  decomposes. 

Sodium  bisulphite  (NaHSO3)  is  formed  by  saturating  sodium  car- 
bonate solution  with  sulphur  dioxide :  — 

Na2CO3  +  H2O  +  2  SO2  =  2  NaHSO3  +  CO2. 

It  forms  a-  strong-smelling  solution  occasionally  used  as  an  "  anti- 
chlor  "  to  remove  excess  of  chlorine  from  the  fibres  of  bleached  cotton 
or  linen  goods.  Its  reaction  is  probably  as  follows  :  — 

Ca(ClO)2  +  2  NaHSO3  =  2  NaCl  +  CaSO4  +  H2SO4;  or, 
=  Na2SO4  +  CaSO4  +  2  HC1 ; 

2  Cl  +  NaHSO3  +  H2O  =  NaCl  +  H2SO4  +  HC1 ;  or, 
=  NaHSO4  +  2  HC1. 


60  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

It  also  finds  some  use  in  other  industries,  such  as  chrome  tannage, 
brewing,  glucose  and  starch  making.  The  solution  of  bisulphite 
decomposes  on  evaporation,  giving  off  part  of  the  sulphur  dioxide, 
and  forming  neutral  sulphite  of  sodium. 

Calcium  bisulphite  [CaH^SOs^]  is  made  by  passing  sulphur  di- 
oxide into  milk  of  lime.  It  is  probably  a  solution  of  neutral  sulphite 
in  an  excess  of  aqueous  sulphurous  acid.  It  is  used  in  much  the  same 
way  as  the  sodium  salt. 

Hydrosulphurous  acid  (H2S2O4)  and  sodium  hydrosulphite  are 
important  bleaching  and  reducing  agents.  The  acid  results  from  the 
action  of  iron  or  zinc  on  aqueous  sulphurous  acid  :  — 

2  H2SO3  +  Zn  =  ZnO  +  H2S2O4  +  H2O. 

The  zinc  oxide  unites  with  another  molecule  of  sulphurous  acid,  form- 
ing zinc  sulphite. 

Sodium  hydrosulphite  (Na2S2O4)*  is  made  by  dissolving  zinc  in 
sodium  bisulphite  :  — 

4  NaHSO3  +  Zn  =  Na2Zn(SO3)2  +  Na^O,  +  2  H2O. 

The  zinc-sodium  sulphite  is  precipitated  with  milk  of  lime,  and  the 
hydrosulphite  is  left  as  a  solution,  which  is  very  unstable,  rapidly 
absorbing  oxygen  from  the  air.  The  hydrosulphite  can  be  precipitated 
from  the  solution  by  adding  salt,  and  cooling  the  liquid,  when  crys- 
tals of  Na2S2O4  •  2  H2O  separate.  By  treatment  with  hot  alcohol, 
the  water  of  crystallization  is  removed,  and  the  anhydrous  powder  is 

SO2Na 
/ 

fairly  stable  if  kept  dry;  its  formula  is  O  .'   It   can   also    be 

SONa 

made  by  treating  metallic  sodium  with  sulphur  dioxide  (gas  or  liquid) 
in  the  presence  of  petroleum  ether. 

Hydrosulphite  combines  with  formaldehyde,  producing  a  stable 
mixture  of  formaldehyde  compounds  of  sodium  sulphoxylate,  and 
sodium  bisulphite  :  — 

SO2Na  SONa  SO2Na 


O  +2CH2O  +  H2O  =  0  +0 

SONa  CH2OH  CH2OH 

(sulphoxylate)      (bisulphite) 

•*Bernthsen,  Ber.  13,  2277;  14,  438;  33,  126. 


SULPHUR  61 

This  mixture  is  much  used  under  various  trade  names,  hydrosulphite 
NF,  rongalite  C,  hyraldite,  decroline,  blanchite,  etc.,  as  reducing,  bleach- 
ing, and  discharge  agents  in  textile  industries.  By  treatment  with 
zinc  dust,  the  bisulphite-formaldehyde  is  converted  into  the  sulph- 
oxylate-formaldehyde  (NaHSO2  •  CH2O  -  2  H2O),  which  is  sold  as 
hydrosulphite  NF,  cone.  ;  hyraldite  C,  extra,  etc. 

Sodium  thiosulphate  (Na2S2O3  •  5  H2O),  sold  under  the  trade  name 
"  hyposulphite  of  soda"  is  made  by  digesting  sulphur  with  a  solution 
of  neutral  sodium  sulphite,  or  sodium  hydroxide  :  — 


Na2SO3  +  S  = 

6  NaOH  H-  12  S  =  Na^Og  +  2  Na2S5  +  3  H2O. 


It  is  also  obtained  from  the  waste  sulphide  liquors  of  the  Leblanc 
soda  process  (p.  104).  It  is  largely  used  in  chrome  tannage,  in  photog- 
raphy, in  wet  silver-extraction  processes,  as  antichlor  in  paper  bleach- 
ing (p.  562),  in  textile  dyeing  and  printing,  for  bleaching  straw,  wool, 
ivory,  etc.,  and  in  iodometry. 


SULPHURIC  ACID 

Sulphuric  acid  is  probably  the  most  important  of  all  chemicals, 
because  of  its  extensive  use  in  a  very  large  number  of  manufacturing 
operations.  Of  the  immense  quantities  made  yearly,  the  greater  part 
does  not  come  upon  the  market;  for,  being  expensive  and  difficult 
to  ship,  consumers  of  large  amounts  generally  make  their  own  acid. 

The  commercial  grades  of  acid  have  special  names.  A  moder- 
ately strong  acid  (50°-55°  Be.),  such  as  condenses  in  the  lead  cham- 
bers, is  known  as  "  chamber  -acid."  It  contains  from  62  to  70  per 
cent  of  H2SO4,  and  is  strong  enough  for  use  in  the  manufacture  of 
fertilizer,  and  for  other  purposes  requiring  a  dilute  acid.  By  con- 
centrating this  chamber  acid,  an  acid  of  60°  Be.  is  obtained,  contain- 
ing about  78  per  cent  of  H2SO4,  which  is  sufficiently  strong  for  most 
technical  uses.  Further  evaporation  in  platinum  or  iron  pans  yields 
an  acid  of  66°  Be.,  containing  93.5  per  cent  of  H^SO^  and  known  as 
oil  of  vitriol,  while  the  strongest  acid  that  can  be  made  by  direct 
evaporation  contains  about  98.5  per  cent  of  H2SO4,  and  is  called 
monohydrate.  Fuming  or  Nordhausen  acid,  which  is  still  more  con- 
centrated, is  prepared  by  special  means,  and  it  is  essentially  a  solu- 
tion, of  sulphuric  anhydride  (SOs)  in  sulphuric  acid ;  this  is  the  acid 
which  was  prepared  by  the  alchemists  in  the  Middle  Ages. 

In  about  the  year  1740,  Ward,  an  Englishman,  began  to  make 
sulphuric  acid  on  a  moderately  large  scale.  He  burned  sulphur  and 
nitre  (KNOs)  together,  and  condensed  the  vapors  in  glass  vessels 
containing  a  little  water.  The  dilute  acid  so  formed  was  then  con- 
centrated in  glass  alembics  or  retorts.  In  this  way  an  acid  was 
produced  at  a  lower  price  than  the  fuming  acid  could  be  made,  and 
the  industry  was  soon  established  on  a  commercial  scale. 

Sulphuric  acid  is  now  made  by  two  important  methods :  the  old 
chamber  process  yielding  dilute  chamber  acid  (p.  74)  directly,  and 
the  newer  contact  processes  yielding  sulphuric  anhydride  (SOs) 
as  first  product,  from  which  any  desired  strength  of  sulphuric  acid 
may  be  made  by  dissolving  in  weak  acid  or  water.  For  producing 
concentrated  acid  the  contact  method  has  proved  generally  more 
economical,  and  is  slowly  displacing  the  old  chamber  process  with  its 
concentrating  plant.  But  for  acid  of  50°-60°  Be.,  the  advantage  is  not 
so  decidedly  in  favor  of  the  newer  method.  It  is  probable  that  the 
lead  chamber  will  not  be  entirely  given  up  for  many  years  to  come. 

62 


SULPHURIC   ACID  63 

The  reactions  involved  in  Ward's  process  are  those  of  the  present 
chamber  process  for  sulphuric  acid.  This  consists  in  bringing  to- 
gether, under  suitable  conditions,  sulphur  dioxide,  oxygen,  and  water 
vapor,  in  the  presence  of  certain  oxides  of  nitrogen.  The  latter 
probably  act  catalytically,  causing  the  oxygen  to  unite  with  the  sul- 
phur dioxide  and  water  to  form  acid.  The  apparent  reaction  is  :  — 

SO2  +  H2O  +  O  =  H2SO4. 

But  this  does  not  represent  the  actual  process,  which  is  more 
complicated  than  it  at  first  appears.  Several  theories  have  been 
advanced  to  explain  the  reactions  occurring  in  the  lead  chambers, 
and  the  part  taken  by  the  nitrogen  oxides,  but  the  most  generally 
accepted  one,  that  of  Lunge,  regards  nitrous  anhydride  (N2O3)*  as 
the  essential  factor,  f  According  to  this  view,  the  principal  reactions 
involved  are  as  follows  :  — 

1)  2  S02  +  N2O3  +  O2  +  H2O  =  2  SO2  •  (OH)  •  (ONO)  (Nitrosyl- 
sulphuric  acid) ; 

2)  2  SO2  •  (OH)  •  (ONO)  +  H2O  =  2  SO2(OH)2  +  N2O3 ;  or, 

3)  2  SO2(OH)(ONO)  +  SO2  +  O  +  2  H2O  =  3  SO2(OH)2  +  N2O3. 

First  there  is  a  union  of  sulphur  dioxide,  nitrous  anhydride, 
oxygen,  and  water,  to  form  nitrosylsulphuric  acid,  which  probably 
separates  as  part  of  the  mist  or  fog  seen  in  the  lead  chambers.  But 
in  the  presence  of  water  vapor  or  of  dilute  sulphuric  acid,  this  nitrosyl- 
sulphuric acid  is  at  once  decomposed,  according  to  reaction  (2),  sul- 
phuric acid  being  formed, -and  nitrous  anhydride  regenerated;  or  if 
sulphur  dioxide  and  oxygen  are  concerned  in  the  process,  then  reac- 
tion (3)  occurs.  This  cycle  of  reactions  repeats  an  indefinite  number 
of  times.  But  in  the  first  lead  chamber,  where  the  temperature  is 
rather  high  and  an  excess  of  water  vapor  is  usually  present,  the  fol- 
lowing secondary  reactions  probably  occur  to  a  greater  or  less  extent :  — 

4)  2  SO2  -  (OH)  •  (ONO)  +  SO2  +  2  H2O  =  3  H2SO4  +  2  NO, 
this  reaction  being  only  momentary. 

*  Ramsey  and  Cundall  (J.  Chem.  Soc.,  1885,  672)  maintain  that  N2Os  exists 
only  as  a  liquid,  and  on  heating,  it  decomposes  into  NO  and  NOs ;  accepting  this 
view,  N2C>3,  as  such,  cannot  be  present  in  the  lead  chambers,  where  the  temperature 
is  over  60°  C. 

t  Hurter  (J.  Soc.  Chem.  Ind.,  1882,  49  and  83)  supports  the  theory  that  nitro- 
gen peroxide  (NO2)  plays  an  important  part  in  the  process. 


64  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

Since  there  is  usually  an  excess  of  oxygen  present,  however,  the 
nitric  oxide  here  formed  is  at  once  brought  into  action  again,  thus :  — 

5)  2  S02  +  2  NO  +  3  O  +  H2O  =  2  SO2  •  (OH)  •  (ONO). 

If  there  is  a  deficiency  of  oxygen,  the  nitric  oxide  is  not  returned 
to  the  process,  but  passes  through  the  several  chambers  and,  since 
it  is  not  absorbed  by  the  concentrated  acid  in  the  Gay-Lussac  tower, 
it  escapes  into  the  atmosphere  and  is  lost. 

The  nitrogen  oxides  are  derived  from  nitric  acid,  or  by  the  action 
of  sulphuric  acid  on  sodium  nitrate  in  the  nitre  pots.  When  nitric 
acid  is  used,  it  must  be  introduced  in  the  form  of  vapor,  or  at  least 
as  a  very  fine  spray,  whereupon  it  reacts  as  follows :  — 

6)  2  SO2  +  2  HNO3  +  H2O  =  2  H2SO4  +  N2O3. 

Perhaps  this  reaction  really  occurs  in  two  stages,  thus :  — 

(a)  SO2  +  HNO3  =  SO2  •  (OH)  •  (ONO) ; 

(6)  2  SO2  •  (OH)  •  (ONO)  +  H2O  =  2  H2SO4  +  N2O3. 

The  formula  assigned  to  the  nitrosylsulphuric  acid   may  perhaps 
OH 

be  written  SO2          ,  and  the  compound  would  then  be  called  nitro- 

NO2 

sulphonic  acid.  But  in  either  case  the  existence  of  the  substance  is 
only  transitory,  it  being  broken  up  at  once  by  the  steam  and  sulphur 
dioxide  present  when  the  process  is  working  properly.  In  case  there 
is  a  deficiency  of  water  vapor  in  the  chambers,  and  especially  if  the 
temperature  falls  too  low,  the  nitrosylsulphuric  acid  may  separate 
as  crystals,  which  deposit  at  various  points  on  the  walls,  forming 
"chamber  crystals."  This  is  an  undesirable  accident,  for  when 
steam  or  water  come  in  contact  with  them,  they  decompose  into  sul- 
phuric acid,  nitric  oxide,  and  nitrogen  peroxide  (N2O4) :  — 

4  S02  •  (OH)  -  (ONO)  +  2  H20  =  4  H2SO4  +  N2O4  +  2  NO.  s 

Then  the  nitrogen  peroxide  unites  with  some  of  the  water, 
N204  +  H20  =  HNO2  +  HNO3, 

forming  nitrous  and  nitric  acids  directly  on  the  walls,  corroding  the 
lead  at  the  point  where  the  cluster  of  crystals  was  attached.  To 
prevent  this  separation  of  "  chamber  crystals  "  or  retention  of  nitro- 


SULPHURIC  ACID  65 

gen  oxides  in  the  sulphuric  acid  an  excess  of  steam  in  the  lead  cham- 
bers is  often  preferred,  although  it  dilutes  the  acid  somewhat. 

Raschig,*  after  an  extended  study  Of  the  process,  maintains  that 
nitrous  acid  (HNO2)  is  present  dissolved  in  the  mist  of  sulphuric  acid 
droplets  filling  the  chamber.  In  the  presence  of  air,  water,  and  excess 
sulphuric  acid,  the  sulphur  dioxide  and  nitrous  acid  combine  to  form 
nitrosisulphonic  acid,  HO  •  SO2  •  NOHO ;  this  then  decomposes  into 
sulphuric  acid  and  nitric  oxide.  Finally  the  nitric  oxide,  reacting 
with  water  and  air,  is  oxidized  to  nitrous  acid.  The  cycle  of  re- 
actions thus  becomes  continuous,  regenerating  nitrous  acid  to  react 
with  new  portions  of  sulphur  dioxide,  as  follows :  — 

1)  2  HNO2  +  SO2  =  H2NSO5  +  NO. 

2)  H2NSO5  =  H2SO4  +  NO. 

3)  2  NO  +  H2O  +  O  =  2  HNO2. 

If,  from  any  cause,  the  proportion  of  nitrous  acid  present  falls  below 
the  quantity  required  by  reaction  (1),  there  is  probably  formed  some 
nitrososulphonic  acid,  thus  :  — 

4)  HN02  +  SO2  =  ONSO3H  or  (NO  •  SO2  •  OH). 

This  may  be  one  of  the  regular  cycle  of  reactions  of  the  process,  but 
if  an  excess  of  nitrous  acid  is  present,  the  nitrososulphonic  acid  passes 
over  at  once  to  nitrosisulphonic  acid  :  — 

5)  HN02  +  ONSO3H  =  H2NSO5  +  NO. 

But  with  an  excess  of  water  vapor  present,  the  nitrososulphonic  acid 
is  hydrolized  to  form  sulphuric  acid  and  nitrous  oxide :  — 

6)  2  (ONS03H)  +  H20  =  2  H2SO4  +  N2O. 

Since  nitrous  oxide  is  not  absorbed  in  the  Gay  Lussac  tower,f  there  is 
here  a  possible  cause  of  the  steady  loss  of  nitrogen  oxides  (nitre)  ob- 
served in  every  chamber  system. 

The  occasional  formation  of  chamber  crystals  when  water  is 
deficient  in  the  chambers  is  due  to  the  formation  of  nitrosulphonic 
acid  (HO  .  SO2 .  NO2),  by  the  oxidation  of  nitrosisulphonic  acid  by  the 
nitric  acid  produced  through  reaction  between  excess  oxygen  and 
nitric  oxide  present  in  the  chamber  gases,  thus :  — 

2  NO  +  2  O  =  N2O4. 

N204  +  H20  =  HN02  +  HN03. 

H2NS05  +  HNO3  +  HNO2  =  HNSO5  +  H2O  +  HNO2  +  NO2. 

*  Zeitschr.  angew.  Chem.,  1905,  1301 ;  1907,  701. 
t  J.  Soc.  Chem.  Ind.,  1906,  149. 
F 


66  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

The  manufacture  of  chamber  acid  is  shown  in  the  diagram  in 
Fig.  25. 

The  acid  may  be  made  from  brimstone,  pyrites,  blende,  hydrogen 
sulphide,  or  the  sulphur  dioxide  produced  in  metallurgical  processes. 
Crude  sulphur  gives  a  pure  acid  free  from  arsenic,  iron,  copper,  or 
zinc,  and  much  smaller  condensing  chambers  may  be  used  for  a  given 
yield  than  when  pyrites  or  blende  is  employed.  Various  types  of 
brimstone  burners  are  in  use  (see  p.  58). 

Pyrites,  or  natural  disulphide  of  iron  (FeSfe),  is  a  dense,  hard 
mineral  of  crystalline  structure  and  pale  yellow  color.  Large 
deposits  in  the  United  States  are  in  Virginia,  at  Mineral  City,  and 
at  Charlemont  in  Massachusetts.  Of  the  foreign  deposits,  those  in 
Spain*  are  the  most  important.  A  pure  pyrites  contains  53.3  per 
cent  of  sulphur,  but  that  commonly  used  for  acid  making  carries 
from  43  to  48  per  cent.  It  seldom  pays  to  use  an  ore  with  less  than 
35  per  cent  of  sulphur,  for  it  will  not  support  its  own  combustion. 

The  first  proposal  to  use  pyrites  originated  with  an  Englishman 
named  Hill,  who  took  out  a  patent  for  the  process  in  1818.  But  it 
was  not  until  1838,  when  the  Sicilian  government  sold  the  monopoly 
of  the  sulphur  export  to  a  French  firm  which  nearly  trebled  the 
price  of  crude  brimstone,  that  pyrites  began  to  find  favor  with  acid 
makers.  At  the  present  time,  because  it  is  cheap  and  easily  obtained, 
pyrites  has  almost  completely  replaced  sulphur  for  acid  making. 
The  product  from  pyrites  is  usually  contaminated  with  arsenic,  and 
often  with  zinc,  copper,  and  selenium. 

By  the  oxidation  of  pyrites  in  a  suitable  furnace,  the  sulphur 
is  converted  to  dioxide,  and  iron  oxide  remains.  The  reaction  may 
be  written  as  follows :  — 

2  FeSs  +  11  O  =  4  SO2  +  Fe2O3. 

This  is  not  exact,  however,  as  some  sulphur  remains  in  the  ore 
and  some  sulphur  trioxide  is  formed.  The  proper  regulation  of  the 
pyrites  burners  is  one  of  the  problems  of  the  manufacturer.  If  the 
ore  contains  over  35  per  cent  of  sulphur,  the  burning,  once  started, 
generates  sufficient  heat  to  maintain  the  combustion,  and  no  fuel 
is  necessary.  But  zinc  sulphide  and  the  "  mattes  "  from  metallurgi- 
cal processes  must  be  heated  by  fuel. 

The  complete  burning  of  pyrites  is  difficult.  With  lump  ore 
there  is  apt  to  be  a  kernel  in  the  centre  of  the  lump,  from  which 

*  Spanish  pyrites  containing  copper  is  much  used  in  England  and  to  some  extent 
in  this  country,  the  burned  cinder  being  afterwards  treated  to  recover  the  copper. 


SULPHURIC   ACID 


67 


the  sulphur  is  not  burned  out.  If  the  temperature  rises  too  high,  the 
charge  fuses  together,  forming  clinkers  or  "  scar,"  and  choking 
the  furnace.  If  too  much  air  is  admitted,  the  furnace  cools  below 
the  temperature  at  which  fresh  pyrites  will  ignite,  and  the  gases  leav- 
ing the  burner  are  so  diluted  that  the  desired  reactions  do  not  take 
place  in  the  lead  chambers.  With  "  smalls  "  the  tendency  to  fuse 
is  more  marked  than  with  lump  ore,  and  the  fine  ore  packs  together 
so  densely  that  the  air  will  not  penetrate  it,  and  unless  it  is  constantly 
stirred  only  the  surface  is  burned.  (The  lump  ore  is  that  which  has 
been  broken  to  about  the  size  of  a  goose  egg,  the  "  smalls  "  constituting 
what  will  pass  through  a  half -inch  screen.) 

Pyrites  burners  are  usually  built  in  benches  containing  from  three 
to  thirty  furnaces,  in  order  that  the  supply  of  gas  may  not  be  broken 
while  charging  or  cleaning  one  furnace. 

A  burner  for  lump  ore  (Fig.  26)  consists  of  a  brick  furnace,  con- 
taining a  grate  formed  of  single  loose  iron  bars  (B,  B)  having  a  square 
section,  and  resting  in 
grooves  at  each  end. 
These  bars  may  be 
turned  parallel  with 
their  longitudinal  axes, 
but  have  no  lateral 
motion.  They  are  so 
adjusted  that  their 
sides  are  at  an  angle 
of  45°  to  the  vertical.  After  a  charge  is  burned,  the  bars  are  given 
several  quarter  turns  by  means  of  a  key,  to  allow  the  cinders  on 
them  to  drop  through  into  the  ash  pit.  Air  is  admitted  by  dampers 
beneath  the  grate.  When  properly  working,  the  cinders  resting  on 
the  bars  are  nearly  cold,  the  hottest  part  of  the  fire  being  eighteen 
inches  above  the  grate.  The  furnaces  are  lined  with  fire-brick, 
and  to  prevent  any  access  of  air  except  through  the  dampers,  the 
doors  (D,  K)  for  charging,  cleaning,  raking,  etc.,  are  made  to  fit 
closely,  and  are  generally  luted  with  clay. 

•  All  the  burners  in  one  bench  deliver  their  sulphur  dioxide  gas 
into  a  common,  wide  flue,  or  "  dust  box  "  (F),  where  any  fine  dust 
carried  along  by  the  gases  may  settle  before  they  enter  the  Glover 
tower.  This  dust  consists  of  unburned  pyrites,  arsenic,  antimony  or 
zinc  oxides,  iron  oxide,  etc. 

In  one  or  more  of  the  burners  a  cast-iron  "  nitre  pot  "  may  be 
set,  in  which  nitrous  gases  are  generated  by  the  action  of  sulphuric 


FIG.  20. 


68 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


acid  on  sodium  nitrate.  Or  the  pots  may  be  placed  in  a  small  chamber 
built  into  the  flue  (F),  and  heated  by  the  waste  heat  of  the  burners. 
Sometimes,  however,  the  pots  are  placed  in  separate  furnaces. 

A  lump  burner  of  average  size  has  a  grate  area  of  15  to  25  square 
feet.  The  furnace  is  sometimes  made  slightly  hopper-shaped  in- 
side, so  that  it  is  larger  at  the  level  of  the  charging  doors  than  at  the 
grate  bars.  About  40  pounds  of  pyrites,  containing  48  per  cent  of 
sulphur,  are  burned  per  square  foot  of  grate  area  in  24  hours,  a  larger 
quantity  of  such  high-grade  ore  being  liable  to  cause  fusion,  unless 
great  care  is  exercised.  A  larger  quantity  of  poorer  ore  may  be 
burned  daily,  without  danger  of  fusion. 

A  number  of  burners  for  fines  have  been  invented,  of  which  the 
Maletra  burner  (Fig.  27)  is  an  early  type.  It  consists  of  a  series 

of  shelves,  about  5  by  8  feet  in  size, 
arranged  in  a  tall  furnace.  The 
smalls,  introduced  through  a  hopper, 
fall  on  the  top  shelf  and  are  spread 
out  by  rakes,  introduced  at  the  door 
(A) ;  they  can  be  dropped  through 
an  opening  (B),  upon  the  next  shelf, 
to  be  again  spread  in  a  thin  layer, 
and  so  on,  each  shelf  being  hotter 
than  the  preceding.  The  spent  cin- 
ders are  taken  out  at  (C).  In  start- 
ing the  furnace,  the  shelves  are 
heated  by  burning  brimstone  or 
fuel,  until  the  walls  are  hot  enough 
to  ignite  the  pyrites,  which  by  their 
combustion  evolve  heat  enough  to  continue  the  burning,  as  long  as  the 
furnace  is  properly  regulated,  and  fresh  ore  supplied  as  needed. 

In  Spence's  furnace,  fines  are  put  into  long  muffles,  externally 
heated. by  waste  heat  from  lump  burners,  or  by  generator  gas,  or  a 
fire ;  this  furnace  is  used  for  roasting  zinc  blende,  copper  mattes,  or 
concentrates,  in  which  the  sulphur  is  too  low  to  burn,  without  external 
heat ;  the  sulphur  dioxide  gas  is  fairly  concentrated. 

Raking  shelf  burners  by  hand  is  heavy  labor  and  permits  the  en- 
trance of  undue  amounts  of  air;  mechanical  raking  obviates  this 
largely,  and  several  appliances  are  in  use. 

The  Herreshoff  burner  *  for  fines  has  been  largely  introduced. 


FIG.  27. 


*  This  burner  is  a  modified  form  of  the  McDougall  furnace  (see  p.  552). 
eral  Industry,  Vol.  VI,  236 ;   XII,  267.     J.  Soc.  Chem.  Ind.,  1899,  459. 


Min- 


SULPHURIC   ACID 


69 


It  is  a  steel  cylinder  about  11  feet  in  diameter,  9  to  10  feet  high,  and 
raised  3  feet  from  the  ground  on  iron  posts.  It  is  lined  with  fire-brick 
and  contains  five  slightly  arched  shelves,  the  top  one  having  holes 
at  the  outer  edge ;  the  next  has  a  central  opening ;  the  third  at  the 
outer  edge,  and  so  on.  The  cinders  are  discharged  at  the  outer  edge 
of  the  lowest  shelf.  A  hollow  cast-iron  shaft,  14  inches  in  diameter, 
passing  through  the  centre  of  the  furnace,  contains  sockets  into  which 
the  cast-iron  rakes  for  moving  the  ore  are  fitted  and  locked  by  a 
simple  lip  catching  in  a  notch.  The  shaft  is  steadied  by  a  side  bear- 
ing at  the  top  of  the  furnace  and  is  turned  by  a  gear  beneath  the  fur- 
nace bottom.  From  the  upper  end  of  the  shaft  a  pipe  extends  into  the 
open  air ;  at  the  bottom  of  the  shaft,  cold  air  is  drawn  in,  and  passing 
up  through  it  and  out  by  the  pipe  at  the  top,  keeps  the  iron  from 
becoming  heated  sufficiently  for  the  sulphurous  gases  to  act  on  the 
metal.  As  the  shaft  is  rotated  continuously,  the  rakes  scrape  the 
fines  down  from  shelf  to  shelf,  fresh 
ore  being  fed  in,  to  maintain  the 
combustion.  Air  for  burning  the 
pyrites  is  admitted  through  dampers 
near  the  bottom  of  the  furnace,  and 
the  hot  gases  pass  under  and  over 
each  shelf  as  they  ascend  to  the  out- 
let at  the  top.  The  rakes  may  be 
easily  replaced  when  broken,  with 
only  a  few  minutes'  delay  (compare 
Fig.  125,  p.  597). 

The  Wedge  furnace  (Fig.  28)  is  a 
recent  development  of  the  mechani- 
cal burner.  It  is  much  larger  than 
the  previously  mentioned  and  has 
five  to  seven  shelves.  A  steel  central 
shaft,  four  or  five  feet  in  diameter  and  protected  from  the  action  of 
the  hot  gases  by  a  fire-brick  covering,  carries  the  stirring  arms  set  in 
cast-iron  holders  riveted  to  the  shaft.  This  shaft  is  supported  on, 
and  rotated  by  a  large  gear  about  12  feet  in  diameter,  which  runs 
on  heavy  rollers  beneath  the  furnace,  and  is  driven  by  a  pinion  and 
pulley.  The  hollow  cast-iron  arms  are  divided  by  a  partition,  which 
causes  the  cooling  water  or  air  to  circulate  through  them,  thus  giving 
some  control  of  the  temperature  on  the  separate  hearths.  Special 
shaped  fire-brick  are  used  in  the  shelves,  which  are  flat  on  top,  so  the 
ploughs  scrape  the  hearths  clean.  The  top  arch  is  used  to  dry  the 


FIG.  28. 


70  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

material,  which  is  then  delivered  at  the  centre  on  to  a  cast-iron  feed 
plate,  so  arranged  that  the  ore  forms  an  air-tight  lute,  preventing  any 
escape  of  sulphurous  gases.  The  large  size  of  the  central  shaft  permits 
of  workmen  entering  same  to  make  repairs,  without  cooling  down  the 
furnace.  These  furnaces  are  built  in  several  styles,  some  with  muffle 
hearths,  for  desulphurizing,  chloridizing,  sulpha tizing,  etc.  (see  p.  594). 
The  Glover  tower,  used  in  nearly  all  sulphuric  acid  works,  is 
placed  next  to  the  burners.  Its  functions  are  to  set  free  the  nitrogen 
oxides  from  the  Gay-Lussac  tower  acid ;  to  cool  the  burner  gases  to  50° 
or  60°  C.  before  they  enter  the  lead  chambers ;  to  furnish  part  of  the 
steam  needed  in  the  lead  chambers ;  and  in  many  works  to  concen- 
trate the  dilute  acid  from  the  lead  chambers  to  a  specific  gravity  of 
1.75.  It  also  increases  the  yield  of  acid  from  a  plant  of  given  lead 
chamber  capacity,  for,  in  addition  to  that  condensed  in  the  chambers, 
some  acid  is  formed  in  the  tower  itself.  The  tower  (20  to  30  feet 
high  and  about  10  feet  across)  is  made  of  sheet  lead,  joined  as  de- 
scribed below,  and  supported  on  a  framework  of  timbers  or  steel. 
It  is  lined  with  acid-resisting  brick  or  segments  of  Volvic  lava,*  laid 
without  mortar,  and  is  filled  with  quartz  lumps,  flint  stones,  or  vitri- 
fied brick.  At  the  top  is  an  apparatus  for  distributing  the  acid,  which 
is  to  run  through  the  tower,  f  The  burner  gases  enter  at  the  bottom, 
and  pass  out  at  the  top,  by  a  pipe  leading  to  the  lead  chambers.  These 
form  the  most  important  part  of  a  sulphuric  acid  plant,  since  in  them 
the  reactions  involved  in  the  formation  of  the  acid  take  place.  They 
are  immense  boxes,  made  by  joining  sheets  of  lead,  and  are  supported 
from  a  strong  timber  or  steel  framework,  by  means  of  lugs  or  strips 
of  lead  attached  to  the  outside  of  the  sheets.  The  joints  cannot  be 
made  with  solder,  but  the  edges  of  the  sheets  are  fused  together  by 
means  of  an  aero-hydrogen  flame,  and  the  process,  called  "  lead  burn- 
ing," is  both  difficult  and  slow.  Steam  or  atomized  water  is  intro- 
duced into  the  chambers  to  supply  water  vapor  as  needed.  Each 
chamber  is  suspended  above  a  large  lead  pan  in  such  a  way  that  the 
acid  collecting  in  the  pan  forms  a  hydraulic  seal  for  the  lower  edge  of 
the  lead  chamber.  These  pans  are  6  or  8  inches  wider  than  the  cham- 
ber, and  have  sides  from  14  to  24  inches  high.  There  is  much  dif- 
ference of  opinion  as  to  the  best  size  and  number  of  the  lead  cham- 
bers.J  There  are  usually  from  3  to  5,  with  a  capacity  of  140,000  to 

*  An  acid-  and  heat-resisting  rock,  found  in  the  Puy  de  Dome*  France. 

t  The  working -of  the  Glover  tower  is  described  in  connection  with  the  Gay- 
Lussac  tower. 

J  The  so-called  "  tangential  "  chambers  of  Meyer  consist  of  large  cylindrical 
lead  chambers,  the  inlet  pipes  placed  tangentially  on  the  sides  and  the  outlet  leading 


SULPHURIC   ACID  71 

200,000  cubic  feet  in  the  system.*  As  a  rule,  the  first  chamber  is  the 
largest,  and  in  it  the  greater  part  of  the  acid  is  formed.  The  individual 
chambers  vary  from  10,000  to  80,000  cubic  feet  (100  by  40  by  20  feet). 
In  this  climate  they  are  enclosed  in  a  building  to  avoid  changes  of 
temperature,  which  should  not  vary  much  from  50°  to  65°  C.  in  the 
first  chamber,  and  15°  above  that  of  the  outside  air  in  the  last ;  f 
and  they  are  usually  elevated,  so  that  the  acid  may  flow  from  them 
by  gravity  to  the  evaporating  pans  often  placed  on  top  of  the  pyrites 
burners ;  and  also  that  the  bottoms  may  be  better  watched  for  leaks. 
To  observe  the  working  of  each  chamber,  small  lead  dishes  are  fixed 
at  various  points  on  the  inside  of  the  chamber  wall,  and  from  these, 
pipes  called  "  drips  "  lead  to  test  glasses  outside,  where  the  density 
of  the  acid  may  be  taken.  A  better  method  is  to  place  the  dish  inside 
the  chamber  at  a  distance  from  the  wall,  supporting  it  above  the 
level  of  the  condensed  acid,  and  connecting  it  by  means  of  a  pipe 
with  a  test  glass  outside.  Glass  panes  are  sometimes  set  at  opposite 
points  in  the  chamber  walls,  so  that  the  color  of  the  gases  may  be 
observed.  In  the  first  chamber  the  color  is  white  and  opaque,  owing 
to  the  copious  condensation  of  acid  vapor,  but  in  the  succeeding 
chambers  the  color  becomes  more  and  more  reddish,  owing  to  the 
excess  of  nitrogen  oxides.  If  the  color  becomes  pale  in  the  last  cham- 
ber, there  may  be  a  deficiency  of  nitrous  gases ;  or  too  much  or  too 
little  steam  J ;  or  the  draught  may  not  be  properly  regulated,  causing 
too  much  or  too  little  oxygen  to  enter  the  chamber.  The  usual  remedy 
is  to  introduce  more  nitre  and  then  to  locate  the  difficulty  and  grad- 
ually bring  the  system  to  its  normal  working  condition. 

From  the  last  lead  chamber  the  gases  pass  to  the  Gay-Lussac 
tower,  whose  purpose  is  to  recover  the  oxides  of  nitrogen.  Sometimes 

from  the  centre  of  the  bottom  and  becoming  the  inlet  to  the  next ;  thus  the  gases 
have  a  spiral  movement  which  insures  intimate  mixing. 

Eng.  Pat.  No.  18376,  1898.     Zeitschr.  angew.  Chem.,  1899,  656:   1900,  739. 

*  The  usual  American  practice  is  to  allow  16  to  22  cubic  feet  of  chamber  capac- 
ity per  each  pound  of  sulphur  burned  per  24  hours.  In  English  practice  for  each 
pound  of  sulphur  burned  per  day,  from  22  to  29  cubic  feet  of  chamber  capacity  is 
provided. 

•  f  Attempts  have  been  made  to  operate  at  higher  chamber  temperatures,  since 
a  larger  yield  per  unit  of  volume  of  chamber  space  is  obtained,  but  these  methods 
have  generally  failed,  doubtless  on  account  of  the  increased  corrosion  of  the  lead. 
Since  a  large  excess  of  sulphur  dioxide  i~  present  in  the  first  chamber,  the  reduction 
of  the  nitrogen  oxides  is  practically  instantaneous  and  the  corrosion  is  correspond- 
ingly low.  Thus  the  maintenance  of  higher  temperature  there  is  feasible  though 
not  in  the  later  chambers  where  the  sulphur  dioxide  is  nearly  gone. 

J-The  steam  is  derived  from  a  boiler,  or  from  the  evaporation  of  water  from  the 
diluted  tower  acid  in  the  Glover  tower. 


72  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

two  towers  are  used,  the  gases  passing  up  through  one  and  then  to  the 
bottom  of  the  other,  and  up  through  this  to  the  chimney.  The  tower 
is  usually  about  50  feet  high,  and  8  to  15  feet  across.  It  is  built  of 
lead,  supported  on  a  frame,  in  much  the  same  way  as  the  Glover.  It 
is  lined  with  a  double  row  of  vitrified  brick  placed  next  to  the  lead 
walls,  and  inside  of  this  is  hard  coke,  or  pottery  rings,  plates,  saucers, 
or  balls.  At  the  top  is  a  distributing  apparatus  to  spread  the  acid 
evenly  over  the  coke.  The  acid  which  flows  down  the  Gay-Lussac 
tower  is  that  which  has  been  concentrated  in  the  Glover  tower  to 
a  density  of  from  60°  to  62°  Be.  (about  1.750  sp.  gr.).  Acid  of  this 
strength  absorbs  the  nitrous  anhydride  (N2O3)  and  the  nitrogen  tetrox- 
ide  (NO2  or  N2O4),  but  does  not  absorb  nitric  oxide  (NO)  or  nitrous 
oxide  (N2O).  With  normal  working  of  the  process,  only  that  part 
of  the  nitrogen  oxides  is  lost  which  is  reduced  to  nitrous  and  nitric 
oxide.  When  an  excess  of  oxygen  is  present,  some  of  the  nitric  oxide 
is  converted  to  nitrous  anhydride,  and  thus  saved.  These  nitrogen 
oxides  are  only  absorbed  when  strong  acid  is  run  through  the  Gay- 
Lussac  tower ;  if  the  acid  is  of  less  than  1.50  sp.  gr.,  it  will  not  absorb 
them  ;  for  best  results  it  should  be  1.75  sp.  gr.  The  solution  of  nitrous 
gases  in  sulphuric  acid,  known  in  the  works  as  "  nitrous  vitriol," 
is  run  into  the  Glover  tower,  where  it  is  diluted  with  water,  or  cham- 
ber acid,  till  its  specific  gravity  is  about  1.6.  As  it  passes  down  the 
tower,  coming  in  contact  with  the  hot  sulphur  dioxide  from  the  burn- 
ers and  steam  from  the  lower  part  of  the  tower,  the  high  temperature 
causes  the  dilute  acid  to  give  out  its  absorbed  nitrous  gases,  which 
mix  with  the  sulphur  dioxide  and  pass  back  into  the  lead  chambers. 
This  process  is  called  denitration  of  the  tower  acid.  The  heat  in  the 
lower  part  of  the  Glover  tower  evaporates  a  considerable  portion  of 
the  water  from  the  acid,  thus  concentrating  it  again  to  a  strength 
sufficient  for  use  in  the  Gay-Lussac,  to  which  the  required  amount 
is  returned,  and  the  remainder  is  added  to  the  acid  which  has  been 
concentrated  in  the  lead  pans  (p.  74).  The  hot  burner  gases  are 
cooled  by  contact  with  the  tower  acid  in  the  Glover  tower  to  between 
50°  and  60°  C.,  the  best  temperature  to  work  the  first  chamber. 

If  the  nitrogen  oxides  go  to  waste  entirely,  about  11  to  13  kilos 
of  sodium  nitrate  must  be  used  with  each  100  kilos  of  sulphur  burned. 
The  recovery  by  means  of  the  Glover  and  Gay-Lussac  towers  reduces 
the  nitrate  consumption  to  4  kilos  or  less,  per  100  kilos  of  sulphur,  while 
a  larger  quantity  of  nitrous  oxides  is  introduced  into  the  chambers, 
causing  the  acid  to  form  more  rapidly  and  in  greater  quantities. 

Some  manufacturers  supply  the  nitrogen  oxides  in  the  form  of 


SULPHURIC   ACID  73 

liquid  nitric  acid,  introduced  into  the  chambers.  This  is  easily  regu- 
lated, admits  no  excess  of  air,  and  causes  no  loss  of  sulphur  dioxide, 
such  as  may  happen  during  the  introduction  of  the  "  nitre."  But  care 
must  be  taken  that  the  nitric  acid  does  not  run  down  the  chamber 
sides,  nor  collect  in  the  acid  on  the  floor,  for  then  the  lead  is  rapidly 
corroded.  Frequently  the  nitric  acid  is  introduced  into  the  Glover 
tower  with  the  tower  acid.  The  cost  of  the  liquid  nitric  acid  must  be 
balanced  against  the  advantages  gained  by  its  use. 

When  sodium  nitrate  is  decomposed  by  sulphuric  acid  in  the  nitre 
pots,  the  nitric  acid  vapor  enters  the  bottom  of  the  Glover  tower  with 
the  sulphur  dioxide.  The  vapors  here  coming  in  contact  with  steam 
begin  to  react  at  once,  probably  as  follows :  — 

2  SO2  +  2  HN03  +     H2O  =  2  H2SO4  +  N2O3 ; 
or,  3  SO2  +  2  HN03  +  2  H2O  =  3  H2SO4  +  2  NO. 

Thus  the  process  of  acid  making  begins  in  the  Glover  tower,  and 
continues  in  the  chambers  according  to  the  reactions  given  on  p.  63. 

Sufficient  sulphuric  acid  is  used  to  form  the  acid  sodium  sulphate 
(NaHSO4).  This  is  liquid  at  the  temperature  prevailing  and  after 
the  reaction  is  ended  is  easily  run  out  through  a  tap  in  the  bottom  of 
the  pot.  On  cooling,  this  acid  sulphate  solidifies,  forming  ".nitre 
cake"  (p.  138). 

Compressed  air  is  employed  to  force  the 
concentrated  acid  from  the  Glover  tower  to 
the  top  of  the  Gay-Lussac,  and  the  nitrous 
vitriol  from  the  Gay-Lussac  to  the  top  of  the 
Glover  tower.  The  acid  collects  in  a  large 
oval  vessel  of  cast-iron,  called  the  acid  egg  FIQ 

(Fig.  29),  and  the  compressed  air  from   (B) 
forces  it  out  through  the  pipe  (A)  to  the  Glover  or  Gay-Lussac  tower. 

Kestner's  acid  elevator  (Fig.  30)  is  much  used ;  a  cast-iron  lead- 
lined  vessel  (B)  has  a  vertical  pipe  (T)  in  which  a  rod  hangs  free, 
extending  from  the  air- valve  case  (D)  to  the  float  (X).  Acid  enters 
through  the  valve  (M)  and  the  pipe  (A),  lifting  the  float  (X),  which 
opens  the  valve  in  (D)  by  the  rod  in  (T),  admitting  compressed  air 
from  the  pipe  (P)  to  (B)  through  (T).  The  air  compressed  in  (B) 
closes  the  valve  (M)  and  forces  the  acid  out  through  the  pipe  (0)  to 
the  desired  elevation.  As  the  acid  level  in  (B)  falls,  the  float  sinks 
until  it  closes  the  air  valve  (D),  while  acid  again  flows  in  through  (A). 
The  apparatus  is  automatic,  simple,  and  occupies  but  little  space. 
Modified  forms  are  used  for  hydrochloric  and  other  acids.  The  acid 


74 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


in  the  cistern  supplying  the  apparatus  must  never  reach  a  higher 
level  than  the  line  (FG). 

The  "air-lift"  pump  (Fig.  31)  is  used  to  some  extent  to  raise 
the  acid  to  the  top  of  the  towers.     A  pipe  (P)  is  sunk  into  the  ground 
to  a  depth  equal  to  the  height  to  which  the 
acid  from  (S)  is  to  be  raised ;  the  air  from 
(R)  is  forced  in  near  the  bottom  of  the  pipe, 
the  pressure  causing  a  rush  of  air  up  the 


FIG.  30. 


FIG.  31. 


pipe,  carrying  before  it  some  of  the  acid,  which  is  thus  thrown  out 
into  (T)  in  "  slugs,"  and  not  in  a  continuous  stream. 

The  acid  condensed  in  the  lead  chambers  varies  from  1.5  to  1.62 
sp.  gr.  If  more  concentrated,  it  absorbs  oxides  of  nitrogen  present 
in  the  chambers,  and  attacks  the  lead. 

In  the  concentration  of  chamber  acid  it  is  first  evaporated  to 
1.70  sp.  gr.  (60°  Be.)  in  shallow  lead  pans  often  heated  by  the  waste 
heat  from  the  pyrites  burners.  Since  acid  stronger  than  1.70  attacks 
lead, '"oil  of  vitriol"  is  made  in  glass  balloons,  or  in  platinum  or 
iron  stills,  or  by  direct  heating  in  the  Glover  tower,  Kessler  apparatus, 
or  dishes  of  porcelain  or  fused  silica. 

Continuous  acting  concentrators,  using  porcelain  or  fused  silica 
(Vitreosil,  etc.)  evaporating  dishes  set  en  cascade  (Fig.  32)  are  con- 
siderably employed.  Quartz  dishes  are  bedded  in  asbestos  rings  on 


SULPHURIC   ACID 


75 


FIG.  32. 


fire-clay  supports,  so  the  flame  strikes  directly  on  the  lower  part  of 
the  vessel,  but  is  not  in  contact  with  the  acid,  nor  with  the  fumes 
from  the  evaporation.  The  acid  over- 
flows from  one  vessel  to  the  next, 
through  a  series  of  some  25  basins. 

Glass  stills  set  in  sand  baths  and 
heated  by  a  fire  are  used  somewhat, 
and  yield  a  very  pure,  colorless,  and  strong  acid  ;  but  owing  to  break- 
age there  is  much  loss  and  some  danger. 

Platinum  stills  (Fig.  33)  are  shallow  platinum  dishes  (S,  S)  cov- 
ered with  a  lead  hood  or  bell  (B),  which  is  kept  cool  by  a  water  jacket. 

The  vapors  condensing 
in  this  hood  as  a  dilute 
acid  do  not  fall  back  into 
the  still,  but  collect  in  a 
narrow  trough  around 
the  lower  edge  of  the 
bell,  and  are  usually  re- 
turned to  the  lead  pans. 
When  the  acid  in  the 
still  has  reached  1.835 
sp.  gr.  (66°  Be.),  it  is 
drawn  off  through  a  platinum  or  lead  cooling  apparatus  (C),  as  "  oil 
of  vitriol."  The  platinum  stills  are  set  directly  over  coke  or  coal 
fires  on  the  grate  (G),  and  are  not  allowed  to  cool  except  for  repairs. 
Platinum  stills  may  have  a  spiral  partition  in  the  pan  which  compels 
the  dilute  acid  to  flow  a  considerable  distance  over  the  hot  still- 
bottom  before  it  escapes  through  a  tube  from  the  central  compart- 
ment. The  rate  of  flow  through  the  still  determines  the  concentration 
of  the  acid. 

If  the  chamber  acid  contains  nitrous  vitriol,  the  platinum  is  often 
attacked.  To  prevent  this,  ammonium  sulphate  may  be  added  to 
the  acid  during  the  concentration  in  the  lead  pans  ;  the  nitrogen  oxides 
are  destroyed,  thus  :  — 


FIG.  33. 


N2O3  + 


=  3  H2O  +  H2SO4  +  4  N. 


Platinum  alloyed  with  iridium  is  more  resistant  to  the  action  of  nitrous 
vitriol.  A  still  invented  by  Herseus  *  consists  of  platinum  lined  with 
a  layer  of  pure  gold  rolled  with  the  platinum,  and  not  electroplated. 
It  resists  the  action  of  concentrated  acid,  but  is  attacked  by  nitrous 

*  J.  Soc.  Chem.  Ind.,  1891,  460  ;    1892,  36. 


76 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


vitriol.     The  average  loss  of  platinum  in  concentrating  to  "  oil  of 
vitriol  "  is  about  1  gram  per  ton  of  acid  produced. 

Cast-iron  stills  for  highly  concentrated  acid  are  much  used  in 
modern  work.  These  are  usually  shallow  iron  retorts,  from  6  to  8 
feet  long,  by  2  to  4  feet  wide,  having  a  low  cover  provided  with  an 
outlet  flue  to  carry  off  the  vapors.  The  still  is  set  so  that  it  is  en- 
tirely surrounded  by  the  flame,  thus  preventing  any  condensation 
of  dilute  acid  on  the  cover.  Fins  are  often  cast  in  the  bottom  to 
make  the  acid  flow  in  a  zigzag  channel  across  the  pan.  Acid  of  1.75 
sp.  gr.  or  over  has  very  little  action  on  chilled  cast-iron,  and  the  stills 
stand  from  two  to  six  months'  constant  use.  The  chamber  acid  is 
first  concentrated  to  about  64°  Be.,  in  lead  and  platinum  pans,  or 
by  running  through  the  Glover  tower,  and  then  the  hot  acid  enters 


Fia.  34.* 

the  iron  still  and  is  brought  up  to  the  desired  strength,  ranging  from 
93  to  98  per  cent  H2SO4.  One  type  of  cast-iron  still  setting  is  shown 
in  Fig.  34  * ;  the  acid  enters  in  a  slow  stream  at  (A),  flows  across  the 
still  and  out  at  (B)  into  the  vessel  (C),  where  any  sediment  (sulphates, 
etc.)  deposits.  From  (C)  the  concentrated  acid  flows  into  the  coolers 
(E,  E). 

Chamber  acid  is  sometimes  concentrated  to  60°  Be.  in  open  lead 
pans  heated  by  steam  in  lead  coils ;  this  gives  a  clean  product,  but  is 
not  so  economical  as  evaporation  by  waste  heat  from  the  burners. 
Over-surface  evaporation  (p.  4)  in  lead  pans  is  occasionally  practised, 
but  yields  a  dark-colored  acid. 

Kessler's  acid-concentrating  apparatus  f  (Fig.  35)  is  a  combina- 
tion of  over-surface  heating  with  a  tower  evaporator.  A  chamber 
(G),  built  of  siliceous  materials  enclosed  in  a  lead  case,  is  divided  longi- 
tudinally by  curtain  partitions  (P,  P) ;  over  this  chamber  is  a  short 
tower  (T),  containing  plates  with  overflow  pipes  (L)  and  porcelain 

*  Trans.  Am.  Inst.  Min.  Eng.,  Vol.  16,  517. 
t  J.  Soc.  Chem.  Ind.,  1892,  434 ;  1900,  246, 


SULPHURIC   ACID 


77 


FIG.  35. 


or  fused  quartz  caps   (J).     The  acid  to  be  concentrated  enters  at 

(K),  flows  over  the  plates,  and  passes  down  by  the  pipes  (L)  from  plate 

to  plate,  and  finally  to  the  chamber  (G),  where  it  lies  about  six  inches 

deep  on  the  floor;    the  curtain  walls  (P)  just  touch  the  surface  of 

the  acid.     The  hot  gases 

from  a  coke  fire  enter  at 

(E),  pass  under  the  lower 

edge  of  the  curtain  walls 

and    into    the    channels 

leading  to  the  tower.     In 

passing   under    the   walls 

(P)  the  hot  gases  bubble 

through  the  shallow  layer 

of  acid  on  the  floor  of  (G), 

thus  concentrating  it ;  the 

vapors  and  hot  gases  then  pass  up  the  tower,  bubbling  through  the 

layers  of  dilute  acid  on  the  tower  plates,  and  pass  off  through  the 

hood  and  vapor  pipe  (V). 

When  chamber  acid  is  concentrated  by  running  through  the  Glover 
tower,  it  is  contaminated  with  iron  from  the  flue  dust  of  the  burners. 
It  is  better  to  further  concentrate  such  acid  in  cast-iron  stills,  since, 
when  the  density  reaches  64°  or  65°  Be.,  a  precipitate  of  ferric  sul- 
phate forms,  which  may  cake  upon  the  platinum  and  cause  it  to  crack. 
The  acid  intended  for  oil  of  vitriol  is  usually  drawn  from  the  lead 
pans,  while  that  which  has  been  through  the  Glover  tower  is  fre- 
quently not  further  concentrated. 

To  secure  the  intimate  mixing  of  the  gases  essential  in  the  lead 
chambers,  Professor  Lunge  invented  his  plate  tower,*  a  tall  lead- 
lined  tower  divided  into  narrow  chambers  by  transverse  stoneware 
plates  (Fig.  36)  perforated  by  small  holes,  and  so  placed  that  the 
holes  are  not  in  line.  By  this  arrangement  the  gases  and  liquids  are 
brought  into  very  close  contact,  and  by  placing  such  a  tower  between 
each  pair  of  adjoining  chambers,  it  is  claimed  that  the  chamber  space 
for  a  given  yield  of  acid  can  be  much  reduced.  The  plates  are  not 
practicable  for  the  Glover  tower,  because  the  heat  is  liable  to  crack 
them,  and  the  small  holes  become  clogged  with  dust,  but  they  may 
be  used  in  the  Gay-Lussac  tower. 

*  Zeitschrift  fur  angewandte  Chemie,  1889,  385.  J.  Soc.  Chem.  Ind.,  1889,  774. 
It  may  be  noted  here  that  these  Lunge-Rohrmann  "plate  towers"  have  found 
much  favor  for  condensing  hydrochloric  acid,  but  are  said  to  obstruct  the  draught 
in  sulphuric  acid  making. 


78 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


M 


'  ': 


I 


FIG.  36. 


The  "  pipe  column  "  *  invention  of  Gilchrist  and  Hacker  and  the 
towers  of  Hart  and  Baileyf  carry  out  the  same  idea  of  mixing  and 

cooling  the  gases  more  thoroughly. 
They  consist  of  towers  containing 
a  number  of  small  lead  pipes  set 
horizontally,  and  open  to  the  air 
at  each  end.  The  gases,  in  pass- 
ing through  the  tower,  impinge 
upon  these  tubes  and  are  thus 
cooled  and  mixed,  while  air,  pass- 
ing through  the  tubes,  cools  them 

also- 

The  Barbier  tower  system,!  in 
which  the  lead  chambers  are  abol- 
ished and  a  series  of  towers  substi- 
tuted, was  carefully  tested  on  a  large 
scale  in  Italy,  but  the  results  were 
not  satisfactory,  §  probably  due  to 
excessive  attack  on  the  lead  due  to 

the  high  temperature  (see  footnote,  p.  71).  The  advantages  claimed  for 
the  system  were  :  it  occupies  less  ground  and  is  cheaper  to  build  than  lead 
chambers ;  it  works  at  high  temperature  (90°  C.),  hence  is  less  influenced 
by  atmospheric  changes,  and  is  suitable  for  either  hot  or  cold  climates  ;  it 
gives  a  larger  yield  of  acid  per  cubic  metre  of  space  than  does  the  chamber 
system. 

While  tower  systems  may  be  further  developed  in  the  future,  the  most 
promising  substitute  for  the  cumbersome  and  expensive  lead  chambers 
will  probably  be  found  in  some  of  the  "  contact  "  processes  (see  below). 

To  assist  in  the  circulation  and  mixing  of  the  gases  in  the  cham- 
bers a  fan  of  iron,  hard  lead,  or  earthenware  is  frequently  placed  in 
the  inlet  pipe,  behind  the  Glover,  or  at  the  end  of  the  system.  This 
makes  the  working  of  the  chambers  uniform  and  independent  of  out- 
side temperature  and  wind. 

Atomized  water  instead  of  steam  is  often  introduced  into  the 
lead  chambers.  This  helps  to  abstract  the  heat  liberated  by  the 
reactions,  and  increases  the  yield  of  acid  per  cubic  foot  of  chamber 
space.  The  water  must  be  in  only  the  finest  mist,  made  by  directing 
a  small  jet,  under  high  pressure,  against  a  flat  disk,  or  by  using  some 
type  of  spraying  nozzle. 

Very  concentrated  acid  may  be  made  by  artificially  cooling  oil 
of  vitriol  of  66.3°  Be.  considerably  below  0°  C.,  when  crystals  of  sul- 


*  J.  Soc.  Chem.  Ind.,  1894,  1142  ;   1899,  459. 
$  Bui.  Soc.  Chim.,  11,  726. 


t  Ibid.,   1903,  473. 

§  J.  Soc.  Chem.  Ind.,  1895,  698. 


SULPHURIC   ACID 


79 


phuric  acid  (monohydrate)  separate,  and  are  quickly  freed  from 
mother-liquor  in  a  centrifugal  machine.  The  crystals  melt  at  10°  C., 
yielding  an  acid  of  99.5  per  cent  H2SO4,  with  only  a  trace  of  water. 


CATALYTIC  PROCESSES 


The  catalytic  or  contact  processes  had  their  origin  chiefly  in  some 
experiments  by  Professor  C.  Winkler,*  on  the  conversion  of  sulphur 
dioxide  into  sulphuric  anhydride  by  the  action  of  certain  catalyzers. 
The  fact  of  this  conversion  has  long  been  known  (Phillips,  Eng. 
Pat.,  1831),  but  no  attempt  to  make  practical  use  of  it  had  been 
made.  In  1878  Winkler  patented  a  method  for  producing  platinized 
asbestos  to  be  used  as  a  contact  substance,  and  soon  after  other  experi- 
menters began  work  along  these  lines. 

These  processes  attract  manufacturers,  since  the  plant  occupies 
less  ground  area  and  does  away  with  the  costly  lead  chambers  and 
the  platinum-pan  concentration ;  all  strengths  of  acids,  from  the 
weakest  to  the  most  concentrated  monohydrate  of  98.5  per  cent 
H2SO4,  and  even  fuming  acid,  can  be  produced  in  the  same  works, 
and  with  comparative  ease.  Further,  no  nitre,  with  the  accompany- 
ing recovery  process,  is  necessary. 

The  raw  materials  are  sulphur  dioxide  and  oxygen  from  the  air, 
to  produce  SOs.  By  solution  of  the  sulphur  trioxide  in  water,  any 
concentration  of  acid  can  be  made. 

The   equation   2  SOz  +  Oz  <^  2  SOs    shows   a    characteristic   gas 

reaction.     The  equilibrium  constant  Kp  =  — ^so;! is  given  in   the 

Pso2Vp02 

following   table;    note   that    dissociation   of    the  trioxide  increases 
rapidly  with  the  temperature  :  — 


Degrees  C. 
K,    .     .     . 

450 

188 

528 
31.3 

579 
13.8 

627 
5.54 

680 
3.24 

727 
1.86 

789 
0.956 

832 
0.627 

897 
0.358 

In  the  absence  of  a  catalyzer  the  rate  of  reaction  is  negligible  below 
400°  C. ;  with  finely  divided  platinum,  combination  may  be  detected 
at  200°  C.,  and  becomes  rapid  above  400° ;  above  500°  to  600°  any 
surface  is  fairly  active  and  burned  pyrites  cinder  may  be  used.  The 
reaction  evolves  21.7  Cal.,  and  unless  the  resulting  rise  of  tempera- 
ture is  controlled  by  dilution  of  the  gases,  and  radiation  of  the  heat, 
reversal  of  the  reaction  and  destruction  of  the  apparatus  results. 

*  Dingl.  J.,  1875,  296  ;  1877,  232  ;  1879,  384. 


80  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

This  necessary  temperature  control  is  secured  by  enclosing  the  reaction 
chamber  within  the  flue,  in  which  the  cold  mixture  of  sulphur  dioxide 
and  air  is  passing  to  the  catalyzer,  thus  cooling  the  contact  mass 
and  apparatus,  and  warming  the  mixed  gases  to  the  initial  temperature. 
Or  regulated  quantities  of  the  cold  mixture  are  passed  into  the  con- 
tact chamber  at  different  points.  By  use  of  spongy  platinum,  the 
reaction  may  be  carried  on  at  400°  to  450°  C.,  with  nearly  quantita- 
tive conversion;  with  less  active  accelerators,  higher  temperatures 
(500°  C.,  or  more)  are  required,  and  oxidation  is  less  complete,  neces- 
sitating recovery  of  the  residual  sulphur  dioxide  from  the  exit  gases. 

The  catalyzers  most  in  use  are  spongy  platinum  and  iron  oxide 
from  pyrites  burners.  The  platinum  mass  may  be  platinized  asbestos, 
or  a  sponge  of  metallic  platinum  disseminated  through  a  porous  mass 
of  non-volatile  soluble  sulphates,  oxides,  or  similar  substance. 

The  presence  of  flue  dust,  sulphur  vapors,  or  of  arsenic,  phospho- 
rus, or  mercury  compounds  in  the  mixed  gases  acts  very  injuriously 
upon  the  contact  mass,  soon  rendering  it  inactive  or  causing  rapid 
destruction  of  the  apparatus.  These  substances  must  be  entirely 
removed  from  the  burner  gases  by  cooling,  scrubbing  with  water, 
injecting  steam,  or  filtering. 

Cast-iron  has  proved  unsuited  for  the  construction  of  the  appara- 
tus, since  fuming  acid  makes  it  crack.  The  cause  of  this  appears  to  be 
the  formation  of  sulphurous  acid  in  the  pores  of  the  iron,  through  the 
reduction  of  the  acid  by  the  action  of  the  iron  itself.  Wrought  iron 
seems  to  be  passive  to  acid  containing  more  than  27  per  cent  of  sul- 
phuric anhydride  and  is  well  suited  to  the  purpose. 

The  contact  process  has  entirely  replaced  the  old  dry  distilla- 
tion of  iron  sulphate  for  fuming  acid;  it  has  also  largely  affected 
the  manufacture  of  monohydrate  and  oil  of  vitriol.  In  this  country,  for 
making  acid  of  50°  to  60°  Be.,  the  old  chamber  process  appears  to  be 
economical,  but  in  large  plants,  maintaining  both  processes,  the  expense 
of  evaporating  the  chamber  acid  is  avoided  when  making  stronger 
grades,  by  adding  contact  sulphur  trioxide  to  the  weaker  acid. 

The  process  of  the  Badische  Anilin  u.  Soda-Fabrik*  at  Ludwigs^- 
hafen,  Germany,  was  the  first  commercially  successful  one.  In  this, 
platinized  asbestos  is  the  contact  material.  The  apparatus  (Fig.  37) 
consists  of  several  vertical  iron  tubes  (R),  containing  perforated 
plates  on  which  the  platinized  asbestos  lies  in  thin  layers,  so  that  it 
does  not  offer  too  much  resistance  to  the  passage  of  the  gases.  The 
burner  gases,  cooled  and  purified,  enter  through  (AA')>  pass  up  the 

*  Ber.  deutsch.  chem.  Ges.,  34  (1901),  4069. 


SULPHURIC  ACID 


81 


FIG.  37. 


space  (S,  S),  between  the  tubes,  thus  cooling  them,  and  thence  through 
(0)  and  (F)  to  the  chamber  (D),  from  which  they  enter  the  tubes, 
pass  down  through  the  contact  mass  and 
out  by  (D')  and  (C).  The  tubes  are  first 
raised  to  the  initial  temperature  by  gas 
burners  at  (H),  the  combustion  gases  pass- 
ing out  at  (L) ;  but  once  started,  the  heat 
of  the  reaction  maintains  the  process.  Thus 
the  reaction  heat  is  utilized  to  bring  the 
mixture  of  SO2  and  air  to  the  initial  tem- 
perature, while  the  reaction  products  are 
cooled  below  the  decomposition  tempera- 
ture. 

The  Grillo-Schroeder  process  *  employs 
platinized  masses  of  soluble  anhydrous  salts, 
such  as  magnesium  or  sodium  sulphate,  as 
contact  mass.  This  becomes  inactive  after 
a  time,  when  the  soluble  salts  are  dissolved  in  water  or  acid  and  the 
platinum  readily  recovered. 

Hasenbach  and  Clemm  propose  to  use  the  iron  oxide  residue 
from  pyrites  burning  as  contact  material.  This  is  not  so  effective 
as  platinum,  and  the  formation  of  sulphur  trioxide  is  not  near  the 
theoretical  amount,  but  the  cheap  material  offers  inducement  for 
experiment.  The  pyrites  cinders  are  introduced,  still  hot,  into  the 
contact  chamber,  which  is  a  vertical  shaft,  and  the  burner  gases 
require  no  purifying.  Dust,  arsenic,  and  other  impurities  are  re- 
tained by  the  iron  oxide  in  the  lower  part  of  the  apparatus,  and 
the  anhydride  is  formed  in  the  upper  part.  The  cinder  is  removed 
periodically,  as  it  becomes  inactive. 

The  difficulty  of  removing  from  the  gas,  dust  and  impurities  (ar- 
senic) which  poison  the  catalyzer  is  very  great,  especially  when  burn- 
ing pyrites.  Frequently  the  gases  are  scrubbed  in  towers  with  strong 
sulphuric  acid,  or  washed  in  spray  chambers  with  a  fine  spray  of  acid  ; 
then  they  are  filtered  through  layers  of  pulverized  coke,  slag,  or  asbestos 
wool,  before  admitting  them  to  the  contact  chamber.  This  difficulty 
of  purifying  the  gases  is  a  large  factor  in  limiting  the  extension  of  the 
contact  process.  The  operation  is  more  sensitive  and  a  higher  grade  of 
labor  is  required  than  for  the  chamber  process,  in  which  the  elaborate 
treatment  of  the  gases  is  unnecessary.  Thus  despite  the  expensive  lead 
chambers  and  high  cost  of  nitre,  the  latter  holds  its  own  for  dilute  acid. 
*  J.  Soc.  Chem.  Ind.,  1899,  584;  1901,  5794 


82  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

FUMING  SULPHURIC  ACID 

By  absorbing  the  sulphur  trioxide  produced  in  the  contact  process 
in  concentrated  sulphuric  acid,  a  brown,  oily  liquid  is  obtained,  which 
fumes  in  the  air,  owing  to  the  escape  of  some  of  the  dissolved  sul- 
phur oxides.  Sulphur  trioxide  fume  cannot  be  dissolved  in  dilute 
sulphuric  acid,  and  hence  concentrated  acid  must  be  used,  which  is 
later  diluted  to  the  desired  strength.  Fuming  acid  ("  Nordhausen 
acid  ")  was  formerly  produced  in  Bohemia  by  the  dry  distillation  of 
basic  iron  sulphates,  obtained  by  weathering  a  kind  of  pyritiferous 
shale.  When  dried  and  heated  in  small  retorts,  decomposition  ensues, 

Fe2(S04)3 '  2  FeSO4  =  2  Fe2O3  +  4  SO3  +  SO2. 

When  absorbed  in  oil  of  vitriol,  these  vapors  produced  the  fuming 
acid. 

REFERENCES 

J.  Soc.  Chem.  Ind.,  1882  +. 

Progress  in  the  Concentration  of  Oil  of  Vitriol.     By  W.  H.  Adams,  Trans. 

Am.  Inst.  Min.  Eng.,  1887-1888.     Vol.  16,  p.  496. 
Mineral  Industry.     1892  +. 

Schwefelsaurefabrication.     Dr.  K.  W.  Jurisch,  Stuttgart,  1893. 
Die  Gegenwartige   Stand  der  Schwefelsaureindustrie.     Gustav  Rauter, 

Braunschweig,  1903. 

Sulphuric  Acid  and  Alkali.     Vol.  I.  3d  ed.     G.  Lunge,  London,  1903. 
Ber.  deutsch.  chem.  Gesell.,  34  (1901),  4069.     R.  Knietsch. 
Zeitschr.  angew.  Chem.,  1905  (18),  1253.     (Chamber  process.) 
Thermodynamik  Technischer  Gasreactionen.    F.  Haber,  Berlin,  1905. 


SALT 

The  sources  of  salt  are :  — 

1.  Sea-water. 

2.  Rock  salt. 

3.  Salt  brines  derived  from  springs,  lakes,  or  wells. 

Atlantic  sea-water,  except  near  the  mouths  of  large  rivers,  aver- 
ages about  3.4  per  cent  of  solid  matter,  of  which  about  75  per  cent 
is  sodium  chloride,  the  remainder  consisting  of  chlorides,  bromides, 
and  sulphates  of  potassium,  magnesium,  calcium,  lithium,  etc.,  with 
minute  amounts  of  other  salts. 

The  concentration  of  sea-water  for  salt  is  carried  on  to  some 
extent  in  warm,  dry  countries  by  solar  evaporation,  the  water  usually 
being  exposed  in  shallow  tanks  or  ponds  to  the  sun's  rays.  Sea- 
water  is  seldom  evaporated  over  fire  because  of  the  cost  of  fuel.  In 
Russia  it  is  allowed  to  freeze  over  the  surface,  and  the  ice,  which  con- 
tains but  little  salt,  is  removed.  This  is  repeated  until  the  brine  is 
sufficiently  concentrated  to  make  the  evaporation  over  fire  profitable. 
Salt  made  from  sea-water  ("sea-salt")  is  coarse  and  is  usually  damp, 
owing  to  the  presence  of  some  magnesium  chloride,  which,  being  a 
deliquescent  substance,  attracts  moisture  from  the  air.  It  is  of  less 
importance  in  this  country  than  that  made  from  other  brines. 

Rock  salt  is  found  in  many  countries,  and  often  very  pure.  In  Eng- 
land, Austria,  Germany,  Spain,  and  Louisiana  are  large  deposits, 
some  so  pure  that  it  is  only  necessary  to  grind  it  for  use,  but  in  most 
cases  it  is  contaminated  with  iron  oxides,  clay,  sand,  and  other  im- 
purities, which  often  necessitate  its  purification.  In  this  country 
it  is  mined  in  New  York,  Kansas,  California,  Utah,  and  Louisiana. 
As  it  does  not  dissolve  so  readily  as  finely  crystallized  salt,  it  is 
preferred  for  many  purposes,  such  as  curing  meat,  preserving  green 
hides,  and  feeding  to  live  stock. 

The  salt  of  principal  interest  in  this  country  is  derived  from 
natural  brines,  found  chiefly  in  New  York,  Michigan,  Kansas,  and 
Ohio,  while  West  Virginia,  Utah,  Texas,  and  Pennsylvania  produce 
lesser  quantities. 

The  New  York  deposits  are  near  Syracuse  and  in  the  neighbor- 
hood of  Warsaw  and  Batavia.  The  Onondaga  (Syracuse)  deposit 
has  been  known  since  the  middle  of  the  seventeenth  century,  but 
that  at  Warsaw,  opened  in  1883,  is  now  the  most  important.  The 

83 


84  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

Michigan  deposits  are  near  Saginaw  Bay  and  Manistee,  a  strong 
brine  being  obtained  by  boring.  Large  amounts  of  brine  are  evap- 
orated near  Salina,  Kansas.  The  Ohio  and  West  Virginia  deposits 
are  in  the  valley  of  the  Ohio  River,  near  Pomeroy  and  Wheeling. 

Brines  are  obtained  by  bored  wells,  8  inches  in  diameter,  similar 
to  those  for  petroleum  (p.  336).  The  wells  are  lined  with  iron  casings 
to  exclude  water  from  the  over-lying  strata.  The  brine  as  it  comes 
from  the  well  has  some  turbidity,  due  to  clay  or  fine  sand,  together 
with  minute  bubbles  of  carbon  dioxide,  with  which  the  brine  is 
usually  charged.  Ferrous  carbonate  is  also  held  in  solution  by  the 
carbon  dioxide,  and  on  exposure  to  the  air  a  yellowish  red  precipitate 
of  ferric  hydroxide  separates.  This  is  usually  hastened  by  adding 
"  milk  of  lime,"  or  soda-ash,  which  also  throws  out  some  of  the  cal- 
cium and  magnesium  salts  from  the  brine. 

"  Solar  salt  "  was  formerly  made  in  large  amounts  at  Syracuse, 
and  is  yet  produced  at  Great  Salt  Lake  in  Utah,  and  in  California, 
from  sea-water.  The  brine  was  exposed  to  the  sun's  rays  in  shallow 
wooden  vats,  from  6  to  8  inches  deep.  During  the  early  part  of  the 
evaporation,  crystals  of  gypsum,  CaSO4  •  2  H^O,  separate  in  clusters, 
which  are  attached  to  the  floor  of  the  vat.  After  the  gypsum  is 
all  separated,  the  brine  is  drawn  into  other  vats,  "  salt-rooms," 
where  evaporation  causes  the  salt  crystals  to  separate.  These  col- 
lect on  the  floor  of  the  vat,  and  two  or  three  times  each  season  the 
salt  is  "  harvested,"  i.e.  raked  up,  freed  from  excess  liquor  in  per- 
forated drainers,  and  removed  to  the  store  house.  Wooden  covers 
over  the  vats,  which  may  be  rolled  back  in  fair  weather,  serve  to  keep 
out  rain.  In  foreign  countries  "  ricks  "  (p.  4)  are  used  to  concentrate 
brines,  prior  to  evaporation  for  crystallization. 

Solar  salt  forms  aggregates  of  the  cubical  crystals,  which  often 
take  a  "  hopper  "  shape,  and  contain  cavities  in  which  small  amounts 
of  mother-liquor  are  retained,  even  after  long  draining.  Since  the 
liquors  contain  considerable  amounts  of  calcium  and  magnesium 
chlorides,  these  contaminate  the  salt  and  cause  it  to  become  moist 
in  damp  weather. 

Strong  brines,  purified  with  milk  of  lime  or  soda-ash,  are  gen- 
erally concentrated  by  use  of  fuel,  several  types  of  evaporator  being 
in  use. 

The  old  "  kettle  process  "*  (Fig.  38),  in  which  the  evaporation  was 
carried  on  in  cast-iron  kettles  (A,  A)  about  4  feet  in  diameter,  set  in  rows 
of  16  to  25  over  a  flue  leading  from  the  fire-box  (G)  to  the  chimney,  has 

*  After  Merrill,  Bui.  N.  Y.  State  Museum,  III,  No.  11. 


SALT 


85 


been  generally  abandoned.  The  brine  was  delivered  through  (P)  to  each 
kettle  and  the  salt  was  raked  out  as  it  crystallized  and  drained  in  the 
basket  (D),  set  over 
the  kettle.  A  special- 
shaped  "  bittern  pan  " 
(B)  was  placed  in  the 
kettle  at  the  start,  and 
left  until  the  salt  began 
to  crystallize,  when  it 
was  lifted  out,  carrying 
much  of  the  calcium 
and  magnesium  sul- 
phates, or  "  bittern," 
which  separates  first 
as  the  brine  evaporates. 


FIG.  38. 


Sometimes   the 
kettles  are  heated  by 
steam  jackets ;  as  all  have  the  same  steam  pressure,  the  temperature 
is  uniform,  and  only  one  quality  of  salt  is  produced. 

Salt  is  also  made  by  the  "  pan  process  "  (Fig.  39)  *  of  direct 
evaporation  over  fire.  Large  wrought-iron  pans  (H,  H),  24  feet 
wide,  100  feet  long,  and  12  inches  deep,  are  used.  These  pans  are 
divided  into  two  sections  by  a  loose  partition,  which  allows  the 
brine  to  flow  slowly  from  the  rear  to  the  front  section.  A  second 
smaller  pan  is  set  behind  and  slightly  above  the  first,  so  that  its 
contents  may  be  syphoned  into  the  front  pan.  Both  are  heated  by 
flues  from  grates  (G),  but  the  rear  one  gets  only  the  waste  heat, 
before  the  gases  pass  into  the  chimney.  The  ends  of  each  pan  are 
made  perpendicular  to  the  bottom,  but  the  sides  are  inclined,  and 
sloping  wooden  platforms  (F,  F),  called  "  drips,"  are  joined  to  them; 
on  these  the  salt  is  drained  when  removed  from  the  pans.  The 
brine  is  purified  with  "  milk  of  lime,"  as  in  the  kettle  process. 

The  pan  process  permits  an  easy  control  of  the  size  of  the  grain. 
For  the  preparation  of  a  very  fine  grained  product,  called  "  factory- 
filled  salt,"  it  is  customary  to  add  a  small  amount  of  sodium  carbon- 
ate to  the  brine ;  this  decomposes  the  chlorides  of  calcium  and  mag- 
nesium and  any  excess  of  caustic  lime  from  the  "  liming."  Then  a 
small  quantity  of  butter,  glue,  or  soft  soap  is  added,  and  forms  an 
insoluble  calcium  soap  with  the  remaining  traces  of  lime,  and  this  is 
removed  by  skimming. 

For  both  the  kettle  and  the  pan  process,  coal  dust  is  used  as  fuel. 

Strong  brine  boils  at  105°-109°  C.,  and  thus  the  heat  in  the  kettle 
and  pan  process  is  sufficient  to  dehydrate  any  calcium  sulphate  in  the 
*  After  Merrill,  Bui.  N.  Y.  State  Museum,  III,  No.  11. 


86 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


salt;  when  dissolved  in  water,  such  products 
cause  a  slight  milkiness,  which  disappears  after 
a  time,  owing  to  the  hydration  of  the  calcium 
sulphate  and  its  solution  in  the  water. 

In  Michigan  and  in  western  New  York  brine 
is  evaporated  in  "grainers"  (Fig.  40)*;  these 
are  long,  shallow  vats  of  wood  or  iron,  contain- 
ing steam  pipes  (P,  P),  through  which  live  or 
exhaust  steam  is  passed.  The  pipes  are  about 


FIG.  40. 

4  inches  in  diameter  and  are  hung  about  6  inches 
above  the  floor  of  the  "  grainer,"  which  is  some 
20  inches  deep.  Once  a  day  the  salt  is  raked  up 
and  deposited  on  draining  platforms  over  the 
grainers.  The  brine  is  purified  before  evapora- 
tion, as  in  the  pan  process,  and  is  supplied  to 
the  grainer  in  just  sufficient  quantities  to  replace 
the  water  evaporated.  When  the  mother-liquors 
become  too  highly  charged  with  calcium  and 
magnesium  chlorides,  they  are  drawn  into  special 
grainers,  and  a  low  grade  of  salt  is  made  from 
them. 

Brine  is  frequently  evaporated  in  continu- 
ous-acting vacuum  pans,  and  a  finely  crystalline 
product,  the  best  grade  of  table  and  dairy  salt, 
results.  It  is  separated  from  adhering  mother- 
liquor  by  the  centrifugal  machine. 

Sometimes  pure  water  is  introduced  into  rock 
salt  deposits  through  tube  wells ;  when  saturated 
with  salt,  it  is  pumped  to  the  surface  and  evap- 
orated. A  much  stronger  brine  than  is  found 
in  nature  is  secured  in  this  way. 

*  After  Merrill,  Bui.  N.  Y.  State  Museum,  III,  No.  11. 


SALT  87 

In  Michigan,  West  Virginia,  Germany,  and  other  places  large 
quantities  of  bromine  are  recovered  from  the  mother-liquors  (also 
called  "  bittern  ")  from  the  salt  industry. 

In  Italy,  Austria,  and  China  the  manufacture  and  sale  of  salt  is 
a  government  monopoly.  In  France,  Germany,  and  India  salt  used 
for  seasoning  food  is  subject  to  tax.  When  used  for  technical  pur- 
poses, or  in  agriculture,  the  tax  is  very  small.  To  prevent  fraud, 
all  German  salt,  not  intended  for  table  use,  must  be  mixed  with  cer- 
tain substances  to  render  it  unfit  for  eating.  Some  of  these  adulter- 
ants are  iron  oxide,  crude  petroleum,  coal  dust,  pyrolusite,  carbolic 
acid,  mineral  acids,  sodium  sulphate  or  carbonate,  alum,  soot,  etc. 

REFERENCES 

Die  Industrie  von  Stassfurt  und  Leopoldshall.     G.  Krause,  Cothen,  1877. 

Report  on  Manufacture  of  Chemical  Products  and  Salt.  W.  L.  Row- 
land, United  States  Census,  1880 ;  Washington,  1884. 

Mineral  Resources  of  the  United  States.     (1882  +.) 

Chemische  Industrie.     1883,  225.     G.  Lunge. 

Report  of  the  State  Geologist  of  New  York,  1885,  pp.  12-47.     I.  P.  Bishop. 

Jour.  Soc.  Chem.  Ind.,  1888, 660.   On  the  Tees  Salt  Industry.   T.  W.  Stuart. 

Die  Salz  Industrie  von  Stassfurt.     Dr.  Precht,  1889.     (Weicke,  Stassfurt.) 

Bulletin  of  the  New  York  State  Museum,  Vol.  Ill,  No.  11.  Salt  and 
Gypsum  Industries  of  New  York.  F.  J.  H.  Merrill,  Albany,  1893. 

Forty-seventh  Report  of  the  State  Museum  of  New  York,  pp.  205-257. 
The  Livonia  Salt  Shaft.  James  Hall,  1894. 

Journal  of  the  Society  of  Arts,  1894.     Manufacture  of  Salt.     F.  Ward. 

Salt  Deposits  and  Salt  Industry  in  Ohio.  J.  A.  Bownocker,  Ohio  Geol. 
Survey,  Bull.  8,  Vol.  IX,  1906. 

Gewinnung  und  Reinigung  des  Kochsalzes.  Carl  Riemann,  Halle,  a.  S., 
1909. 

Louisiana  Salt  Mines.    P.  Wooten,  Min.  Eng.  World,  1912,  401. 

The  Salt  Industry  of  Michigan.  C.  W.  Cook.  Mich.  Geol.  Survey,  Pub. 
8,  1912. 


HYDROCHLORIC  ACID  AND  SODIUM  SULPHATE 

Hydrochloric  or  muriatic  acid  is  generally  made  by  the  action  of 
sulphuric  acid  on  common  salt.  It  is  a  by-product  of  the  Leblanc 
soda  process,  and  in  the  early  years  of  the  industry  was  allowed  to 
escape  into  the  air,  as  the  demand  for  it  was  small.  But  the  nuisance 
caused  by  the  acid  fumes  in  the  neighborhood  of  the  alkali  works 
became  so  great,  that  in  England  a  very  stringent  law  was  enacted 
forbidding  the  soda  makers  to  allow  more  than  5  per  cent  of  the  gas 
to  escape  into  the  atmosphere.  This  made  it  necessary  to  absorb 
the  acid  fumes  in  water.  The  provisions  of  the  present  "  Alkali  Act  " 
permit  only  0.2  grain  of  hydrochloric  acid  per  cubic  foot  of  chimney 
gas  to  be  discharged  into  the  atmosphere. 

The  Leblanc  industry  has  declined  in  recent  years,  but  there  is  an 
increased  demand  for  hydrochloric  acid,  and  at  present  this  is  one  of 
the  main  products  desired.  Its  chief  use  is  for  the  generation  of 
chlorine  for  the  manufacture  of  bleaching  powder;  now  nearly  all 
soda  makers  also  produce  bleaching  powder,  and  the  profits  derived 
from  the  latter  have  largely  offset  the  decline  in  returns  from  soda- 
ash.  Up  to  the  present,  no  better  method  than  the  above  has  been 
devised  for  making  this  acid.  The  process  may  be  represented  by  the 

equation :  — 

2  NaCl  +  H2SO4  =  Na2SO4  +  2  HC1. 

But  as  actually  carried  out  it  takes  place  in  two  stages,  according 
to  the  following  reactions  :  — 

1)  NaCl  +  H2S04  =  NaHS04  +  HC1. 

2)  NaHSO4  +  NaCl  =  Na2SO4  +  HC1. 

These  reactions  may  be  carried  out  by  heating  the  mixture  of 
salt  and  sulphuric  acid  either  in  an  "open  roaster,"  or  in  a  muffle  or 
"  close  roaster."  These  are  both  called  "  salt-cake  furnaces." 

The  open  roaster  (Fig.  41)  consists  of  two  parts,  the  cast-iron 
pan  (A)  and  the  reverberatory  hearth  (C).  The  salt  and  sulphuric 
acid  (60°  Be.,  sp.  gr.  1.72)  are  put  into  the  pan  (A),  and  are  moder- 
ately heated  by  a  fire  on  the  grate  (E).  The  first  reaction  takes 
place  at  a  comparatively  low  heat,  and  the  hydrochloric  acid  vapors 
escape  through  the  earthenware  pipe  (B).  Then  the  fused  mass 
of  sodium  acid  sulphate  and  undecomposed  salt  is  raked  up  on  the 
reverberatory  hearth  (C),  where  it  is  exposed  to  the  high  temperature 

88 


HYDROCHLORIC  ACID   AND   SODIUM   SULPHATE 


89 


of  the  flame  from  (D).  This  completes  the  second  reaction,  and  a 
pasty  mass  of  normal  sodium  sulphate  is  formed.  The  hydrochloric 
acid  vapors,  set  free 

during   the    reaction,  gp 

mix  with  the  furnace 
gases  from  (D),  and 
escape  through  the 
pipe  (F)  to  the  ab- 
sorbing apparatus. 
The  furnace  gases 

dilute  the  acid  vapors  so  much  that  a  very  concentrated  solution 
of  hydrochloric  acid  cannot  be  made  with  the  open  roaster ;  however, 
it  yields  acid  strong  enough  for  use  in  Weldon's  chlorine  process 
(p.  117).  Moreover,  the  soot  and  dust  from  the  furnace  at  (D)  con- 
taminate the  acid,  and  may  cause  clogging  in  the  passages  and  pipes 
of  the  absorption  apparatus.  The  open  roaster  has  the  advantage 
over  the  close  roaster  that  it  yields  more  sodium  sulphate  with  smaller 
consumption  of  fuel.  The  crude  sodium  sulphate,  called  "  salt-cake," 
usually  contains  a  little  undecomposed  salt  and  a  slight  excess  of 
sulphuric  acid. 

The  muffle  or  "  close  roaster  "  is  used  very  generally  on  the  con- 
tinent of  Europe,  and  yields  a  stronger  and  purer  acid  than  the  open 
roaster.  The  usual  form  is  shown  in  Fig.  42.  The  pan  (A)  is  built  very 

much  as  in  the  open 
roaster,  but  is  heated 
by  the  furnace  gases 
from  the  grate  (D). 
The  acid  vapors  set 
free  in  the  pan  es- 
cape by  the  pipe 
(C)  to  the  absorption  apparatus.  The  muffle  (B)  is  made  of  fire-clay 
or  brick,  and  is  heated  by  the  flames  from  the  grate  (D).  The 
mixture  of  acid  sulphate  and  salt  is  raked  from  the  pan  (A)  into 
the  muffle  (B),  where  it  is  heated  to  a  red  heat,  and  the  acid  vapor 
liberated  passes  through  the  pipe  (E)  to  the  absorption  appara- 
tus. In  this  form  of  roaster  the  soot  and  dust  from  the  grate  are 
kept  away  from  the  acid  vapor,  and  a  concentrated  acid  vapor  is 
obtained,  which  favors  the  formation  of  a  concentrated  solution  of 
hydrochloric  acid  in  the  absorbers.  But  the  muffles  are  expensive 
to  build,  yield  a  smaller  output  of  salt-cake,  and  require  more  fuel 
than  the  open  roaster.  Moreover,  they  often  crack,  thus  permit- 


Fia.  42. 


90 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


ting  acid  vapors  to  escape  into  the  flues  and  chimney,  causing  loss 
and  creating  a  nuisance.  It  is  customary  to  maintain  a  slight  pres- 
sure ("plus  pressure")  in  the  flues  and  chimney,  so  that  if  the 
muffle  cracks,  the  flue  gases  force  their  way  into  it.  This  may  cause 
a  slight  contamination  of  the  acid,  but  no  nuisance  is  created. 
Cheaper  fuel  may  be  used  with  these  furnaces,  but  repairs  are  apt  to 
be  expensive. 

The  pan  (A)  in  both  furnaces  is  about  10  feet  in  diameter,  7  inches 
thick  at  the  centre,  and  3  inches  thick  at  the  sides.  After  a  charge 
is  drawn,  the  pan  is  cooled  somewhat  before  introducing  another, 
for  cold  salt,  coming  in  contact  with  the  hot  pan,  might  crack  it. 
The  sulphuric  acid  is  generally  heated  to 
100°  or  130°  C.  for  the  same  reason. 

During  the  second  reaction,  the  charge  is 
constantly  stirred  with  a  "  rabble,"  a  large 
hoe-shaped  tool,  to  prevent  "  crusting  "  or 
burning  on  to  the  hearth  or  retort.  The 
stirring  is  very  heavy  work  and  the  work- 
men are  sometimes  careless,  and  allow  a 
crust  to  form,  which  may  crack  the  muffle. 
Hence,  many  attempts  have  been  made  to 
construct  mechanical  stirrers.  Of  these,  the 
Mactear  furnace  *  is  most  successful,  but  the 
difficulty  of  protecting  the  driving  mechanism 
from  the  acid  fumes,  and  the  cost  of  building 
and  heavy  up-keep  charges,  have  caused  gen- 
eral abandonment  of  mechanical  furnaces. 

If  salt-cake  free  from  iron  is  desired,  lead 
pans  instead  of  cast-iron  ones  are  used.  But 
these  are  easily  overheated  or  injured. 
The  hydrochloric  acid  gas  is  absorbed  in  water,  by  passing  through 
tall  towers  (Fig.  43)  f  filled  with  coke,  over  which  water  trickles ;  or 
in  a  series  of  large  earthenware  Woulff  bottles  (bombonnes  or  tourills, 
Fig.  44  {),  with  an  absorption  tower  at  the  end  to  catch  acid  gas  which 
may  pass  through  the  bottles.  These  are  set  en  cascade  §  and  the  side 
tubulatures  joined  so  that  a  stream  of  dilute  acid  from  the  tower 
flows  through  them  in  opposite  direction  to  the  movement  of  the  gas. 

*  Chemische  Industrie,  1881,  253.    J.  Soc.  Chem.  Ind.,  1885,  534. 
t  After  Lunge. 

J  Metal.  Chem.  Eng.,  1911,  611. 

§  That  is,  on  a  series  of  steps,  so  that  each  stands  slightly  lower  than  the  one 
preceding. 


FIG.  43. 


HYDROCHLORIC  ACID  AND   SODIUM   SULPHATE       91 


The  standard  absorber  is  difficult  to  cool  externally  with  water  and 
presents  relatively  a  small  liquid  surface  to  the  gas.     A  modified  form 

(Fig.  45)  *  is  claimed  to  be  better,  as 
it  affords  greater  liquid  surface  exposure, 
and  can  be  readily  water-cooled. 

The   Lunge-Rohrmann   plate   tower 


FIG.  44. 


FIG.  45. 


(p.  77)  has  been  tried  with  some  success  as  a  substitute  for  the  coke 
tower  and  bombonnes,  for  hydrochloric  acid  absorption. 

The  condensation  of  hydrochloric  acid  vapors  is  not  so  simple  a 
process  as  it  at  first  appears.  The  gases  coming  from  the  roasters 
are  very  hot,  and  must  be  cooled  before  they  can  be  absorbed  to 
form  a  strong  acid.  Moreover,  with  open  roasters,  there  is  a  large 
amount  of  inert  gas  present  (nitrogen  and  carbon  dioxide  from  the 
fire)  which  dilutes  the  acid  vapors.  Then,  too,  the  vapors  are  not 
set  free  regularly  in  any  roaster,  there  being  a  rapid  evolution  during 
the  progress  of  the  first  reaction,  and  a  much  slower  liberation  during 
the  second.  This  may  cause  a  temporary  rush  of  vapors  through  the 
apparatus,  so  that  they  cannot  be  properly  taken  up  by  the  water. 

The  ordinary  muriatic  acid  of  trade  is  an  aqueous  solution  of  the 
acid  vapor,  having  a  specific  gravity  of  about  1.20  and  containing 
about  40  per  cent  by  weight  of  dry  hydrochloric  acid  vapor.  It  is 
impure,  containing  sulphuric  acid,  chlorine,  iron  chloride,  arsenic, 
and,  generally,  lead  and  calcium  chlorides.  Its  yellow  color  is  partly 
due  to  organic  matter,  and  sometimes  to  iron  and  free  chlorine.  To 
remove  arsenic  and  sulphuric  acid,  the  acid  is  diluted  to  1.12  sp.  gr., 
and  barium  sulphide  is  added;  a  pure  hydrochloric  acid  vapor  is 
then  driven  out  by  distillation  and  absorbed  in  pure  water.  Or  a  solu- 
tion of  stannous  chloride  in  concentrated  hydrochloric  acid  is  added 
to  the  crude  acid,  which  latter  must  have  a  strength  of  at  least  1.15 
sp.  gr.  A  brown  precipitate  of  arsenic  with  some  tin  separates  and 
is  removed  by  decantation.f  Sulphuric  acid  alone  is  removed  by 

*  Metal.  Chem.  Eng.,  1911,  611. 

t  3  SnCh  +  6  HC1+  As2O3  =  As2  +  3  H2O  +  3  SnCh. 

2  AsCls  +  3  SnClz  =  As2  +  3  SnCh. 
This  leaves  stannic  chloride  in  the  acid. 


92  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

adding  barium  chloride  and  redistilling.  To  remove  chlorine,  the 
crude  acid  is  digested  with  strips  of  copper  for  some  hours.  This 
precipitates  arsenic,  and  the  chlorine  combines  with  the  copper.  The 
acid  is  then  redistilled. 

Attempts  to  recover  hydrochloric  acid  from  the  waste  liquors  of 
the  ammonia  soda  process  (p.  122)  have  not  proved  very  successful. 
The  magnesium  chloride  mother-liquors  from  the  potash  salts  of 
Stassfurt  (p.  160)  may  be  decomposed  by  distillation  with  steam, 
and  a  dilute  hydrochloric  acid  obtained. 

MgCl2  +  H2O  =  2  HC1  +  MgO. 

But  this  has  not  proved  a  commercial  success. 

The  Hargreaves  and  Robinson  process  for  the  direct  production 
of  hydrochloric  acid  and  sodium  sulphate  from  salt,  sulphur  dioxide, 
water,  and  oxgyen  is  of  some  importance.  The  damp  salt  is  pressed 
into  blocks  and  dried  ;  it  is  then  charged  into  vertical  cast-iron  retorts, 
a  number  of  which  are  connected  in  a  series.  These  are  heated  from 
without;  the  temperature  of  the  reaction  is  from  400°  to  550°  C. 
The  sulphur  dioxide,  steam,  and  air  are  made  to  pass  through  all 
the  retorts  in  succession,  the  hydrochloric  acid  being  carried  along 
with  them.  A  slight  excess  of  sulphur  dioxide  and  steam  is  used  to 
prevent  the  mutual  reaction  between  the  hydrochloric  acid  vapor 
and  the  oxygen,  by  which  chlorine  is  set  free.  The  decomposition 
being  slow,  the  gases  must  be  kept  in  contact  with  the  salt  for  a 
considerable  length  of  time  ;  a  cylinder  containing  40  tons  of  material 
requiring  from  15  to  20  days'  continuous  action  to  secure  complete 
conversion. 

The  process  is  an  uninterrupted  one  ;  for  as  soon  as  no  more  sul- 
phur dioxide  is  absorbed  in  a  given  cylinder,  it  is  cut  out  from  the 
series,  the  sodium  sulphate  removed,  a  new  charge  of  salt  blocks 
introduced,  and  the  cylinder  made  the  final  one  of  the  series;  so 
that  newly  charged  salt  is  exposed  to  the  most  nearly  exhausted 
sulphur  fumes.  The  reaction  representing  the  process  appears  quite 

simple  :  — 

2  NaCl  +  SOa  +  H2O  +  O  =  Na2SO4  +  2  HC1. 


But  the  mechanical  difficulties  encountered  in  working  it  were  great, 
and  only  recently  has  the  process  met  with  any  marked  success. 

Sodium  sulphate  or  salt-cake  is  largely  used  in  the  production  of 
soda  by  the  Leblanc  process,  for  glass  making,  for  ultramarine,  in 
dyeing  and  coloring,  and  to  some  extent  in  medicine.  For  some  kinds 
of  glass  the  salt-cake  must  be  free  from  iron,  and  consequently  it  is 


HYDROCHLORIC  ACID  AND  SODIUM   SULPHATE        93 

made  in  lead  pans.  Or  the  sulphate  may  be  purified  from  iron  and 
excess  of  acid  by  dissolving  it  in  hot  water,  adding  "  milk  of  lime," 
and  stirring  into  it  a  solution  of  bleaching  powder.  The  iron  is  pre- 
cipitated as  hydroxide  and  settles  on  standing.  By  evaporation,  crys- 
tals of  Glauber's  salt  (Na2SO4  •  10  H2O)  are  obtained.  But  generally 
the  purified  solution  is  rapidly  evaporated  to  dryness,  and  the  product 
is  calcined  to  remove  all  the  water. 


REFERENCES 

Berichte  iiber  die  Entwickelung  der  Chemischen  Industrie,  u.s.w.     A.  W. 

Hofmann,  Braunschweig,  1877.     (Vieweg.) 
Darstellung  von  Chlor  und  Salzsaure,  unabhangig  von  der  Leblanc  Soda 

Industrie.     Dr.  N.  Caro,  Berlin,  1893.     (Oppenheim.) 
Sulphuric  Acid  and  Alkali.     3d  ed.,  Vol.  II.     G.  Lunge,  London,  1909. 

(Gurney  and  Jackson.) 
Die  Fabrikation  von  Sulfat  und  Salzsaure.     Theo.  Meyer,  Halle,  a.  S., 

1907. 


THE  SODA  INDUSTRIES 

THE  LEBLANC  SODA  PROCESS 

Nearly  all  the  soda  of  trade  was  formerly  obtained  from  certain 
natural  deposits  of  the  so-called  "  sesquicarbonate,"  or  from  the  ashes 
of  sea  plants.  But  towards  the  end  of  the  last  century,  the  sup- 
ply from  these  sources  became  insufficient  to  meet  the  increasing 
demands.  About  1775  the  French  Academy  of  Science  offered  a 
large  prize  for  a  method  of  making  soda  from  salt.  Among  other 
processes  submitted  was  one  by  Nicolas  Leblanc,  which  seemed  prom- 
ising, and  being  granted  a  patent  in  1791,  he  began  manufacturing 
on  a  commercial  scale.  But  in  the  French  Revolution  his  factory 
was  seized,  the  patent  declared  public  property,  and  no  indemnity 
was  paid  to  him.  Having  lost  all  his  property,  he  finally  committed 
suicide. 

Leblanc's  process  was  so  perfect  and  complete  that  very  slight 
changes,  and  those  only  in  minor  details,  have  been  made  up  to  the 
present.  It  has  been  in  use  for  more  than  a  century,  and  although 
seriously  threatened  by  newer  processes,  it  still  produces  a  large 
part  of  the  world's  supply  of  soda.  Owing  to  the  fact  that  it  pro- 
duces hydrochloric  acid  and  bleaching  powder  as  by-products,  it  has 
been  able  to  survive  competition,  although  its  condition  is  becom- 
ing more  desperate  every  year.  Its  chief  rival  is  the  ammonia  or 
Solvay  process.  Within  a  few  years  many  electrolytic  methods  for 
caustic  soda  have  appeared,  and  the  extensive  production  of  bleach- 
ing material  by  any  of  these  processes  will  sweep  away  about  the 
only  source  of  profit  left  to  the  Leblanc  manufacturer.  It  is  not 
probable  that  this  change  will  come  immediately,  although  several 
electrolytic  processes  have  proved  fairly  successful  on  a  large  scale; 
but  the  decline  of  the  Leblanc  process  is  generally  regarded  as  inevi- 
table, and  inventors  have,  for  the  most  part,  abandoned  further 
attempts  to  improve  it. 

The  reactions  of  the  Leblanc  process  are  generally  expressed  as 
follows :  — 

1)  2  NaCl  +  H2S04  =  Na2SO4  +  2  HC1. 

2)  Na2SO4  +  2  C  =  Na2S  +  2  CO2. 

3)  Na2S  +  CaCO3  =  Na2CO3  +  CaS. 

4)  CaCO3  +  C  =  CaO  +  2  CO. 

94 


THE    SODA   INDUSTRIES 


95 


But  these  equations  *  do  not  represent  all  the  reactions  which  take 
place  during  the  process,  for  a  number  of  other  substances  are  formed. 
The  first  equation  represents  the  preparation  of  sodium  sulphate  and 
hydrochloric  acid  (p.  88).  The  second  and  third  reactions  are  real- 
ized in  one  operation.  The  fourth  has  no  direct  relation  to  the  process, 
as  the  formation  of  carbonic  oxide  does  not  become  marked  until  all 
the  salt-cake  has  been  decomposed.  This  serves  to  indicate  the  end 
of  the  process,  and  aids  in  the  formation  of  a  porous  product. 

The  salt-cake  should  be  friable  and  porous,  containing  very  little 
free  sulphuric  acid,  and  no  undecomposed  chloride.  The  carbon 
is  supplied  in  the  form  of  powdered  coal,  which  should  contain  very 
little  ash-forming  impurity.  A  little  pyrite  does  no  harm,  but  the 
coal  should  be  as  free  as  possible  from  nitrogen,  in  order  to  prevent 
the  formation  of  cyanides  and  cyanates.  Calcium  carbonate  in  the 
form  of  pure  limestone  or  chalk,  crushed  to  the  size  of  a  small  pea, 
is  mixed  with  the  crushed  salt-cake  and  coal  in  order  to  carry  out 
the  third  reaction.  If  the  limestone  contains  magnesia  or  silica, 
there  is  a  consequent  loss  as  insoluble  residue.  Usually  100  pounds 
of  salt-cake,  100  pounds  of  limestone,  and  50  pounds  of  coal  dust 
form  a  charge.  This  is  an  excess  of  limestone,  the  purpose  of  which 
is  explained  below. 

The  reactions  are  carried  out  in  a  "  black-ash  "  or  "  balling  fur- 
nace," which  may  be  worked  either  by  hand  or  mechanically.  The 
hand-worked  furnace  is  a  long  reverberatory  (Fig.  46).  The  charge 


FIG.  46. 


is  introduced  on  the  platform  (A)  nearest  the  flue,  where  the 
heat  is  not  high.  When  well  heated,  it  is  raked  on  to  the  front 
platform  (B),  which  is  a  few  inches  lower  than  (A).  Here  the  tem- 

*  Lunge  (Sulph.  Acid  and  Alkali,  Vol.  II,  460  et  seq.)  regards  the  theory  of 
Scheurer-Kestner  (Comptes  rendus,  57,  1013,  and  58,  501)  as  correct,  viz.  that 
the  reactions  are  :  — 

5  Na2SO4  +  10  C  =5  Na2S  +  10  CO*. 

5  Na2S  +  5  CaCO3  =  5  Na2CO3  +  5  CaS. 
2  CaCOs  +  2  C  =  2  CaO  +  4  CO. 

While  these  equations  closely  represent  the  net  result,  the  first  and  last  re- 
actions each  yield  mixtures  of  CO2  and  CO,  depending  on  the  temperature  and 
equilibrium  conditions. 


96 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


perature  is  high,  usually  about  1000°  C.,  and  the  surface  of  the  mass 
soon  begins  to  fuse.  It  is  then  raked  over,  thoroughly  exposing  it 
to  the  direct  heat  until  it  becomes  a  thick,  pasty  mass,  from  which 
carbon  dioxide  is  escaping  freely.  After  the  salt-cake  is  all  decom- 
posed, the  charge  begins  to  stiffen,  and  the  evolution  of  carbon  mon- 
oxide is  shown  by  the  appearance  of  jets  of  blue  flame,  known  to  the 
workmen  as  "  candles."  The  charge  is  then  raked  together  into  a 
"  ball,"  which  is  drawn  out  of  the  furnace  into  an  iron  barrow.  The 
evolution  of  carbon  monoxide  continues  for  a  few  minutes  after 
the  "  ball  "  is  removed,  and  the  bubbles  escaping  from  the  pasty  mass 
cause  it  to  become  porous.  The  formation  of  this  gas  is  due  to  the 
action  between  the  coal  and  the  excess  of  limestone  according  to 
reaction  (4).  The  caustic  lime  formed  here  slakes  during  the  lixiv- 
iation  of  the  black-ash  (p.  97),  and  swells,  thus  disintegrating  the 
mass. 

Although  the  heavy  tools  are  suspended  by  chains,  their  operation 
is  still  so  difficult,  and  the  temperature  is  so  high,  that  a  man  cannot 
handle  much  more  than  300  pounds  at  one  time.  In  order  to  work 


larger  charges,  without  the  expensive  hand  labor,  revolving  black- 
ash  furnaces  (Fig.  47)  are  much  used.  These  are  similar  to  the  re- 
volving furnaces  described  on  page  21 ;  the  flame  from  the  furnace  (A) 
passes  through  the  cylinder  (B).  The  charge  is  introduced  through 
the  manhole  (P),  and  the  finished  product  discharged  through  the 
same  opening,  into  the  wagon,  at  the  end  of  the  operation.  The 
cylinder  is  about  16  feet  long  by  10  feet  in  diameter,  and  is  revolved 
by  a  gear  (E)  connected  with  an  engine.  Projections  are  fixed  in  the 
lining  to  help  mix  the  contents.  The  charge  is  usually  about  two 
tons  of  salt-cake,  with  proportionate  amounts  of  coal  and  limestone. 
It  is  customary  to  introduce  only  the  limestone  and  a  part  of  the  coal 
at  first,  and  to  rotate  the  cylinder  until  some  caustic  lime  is  formed ; 
then  the  remainder  of  the  coal,  together  with  the  salt-cake,  is  intro- 
duced, and  the  rotation  continued  until  the  reactions  are  completed. 
The  speed  varies  from  one  revolution  in  three  or  four  minutes,  at  first, 


THE    SODA   INDUSTRIES  97 

to  four  or  five  revolutions  per  minute  during  the  last  part  of  the 
process. 

The  hot  gases  from  the  black-ash  furnace,  whether  hand-worked 
or  mechanical,  pass  through  the  dust  box  (N),  and  then  through  the 
long  flue  over  the  pan  (J,  J)  on  their  way  to  the  chimney  (D).  In 
this  shallow  pan,  the  liquor  obtained  by  lixiviating  the  black-ash  is 
evaporated.  When  crystallized,  the  salts  are  removed  through  the 
small  doors  (J). 

Black-ash  is  a  brownish  black  or  dark  gray  substance  of  a  pumice- 
like  texture,  containing  about  45  per  cent  sodium  carbonate,  30  per 
cent  calcium  sulphide,  10  per  cent  caustic  lime,  and  from  10  to  12 
per  cent  of  other  impurities,  —  sulphate,  silicate,  aluminate,  and 
chloride  of  sodium,  calcium  carbonate,  coal,  and  iron  oxide,  with 
traces  of  cyanides  and  of  sulphides  of  sodium. 

The  next  stage  in  the  process  is  the  lixiviation  of  the  black-ash. 
This  presents  some  difficulties :  if  the  black-ash  is  put  directly  into 
cold  water,  it  often  agglomerates  in  hard  lumps,  which  dissolve  ex- 
ceedingly slowly ;  the  free  lime  present  forms  calcium  hydroxide, 
which  reacts  with  the  sodium  carbonate  solution,  forming  some  caustic 
soda ;  the  solution  of  sodium  carbonate,  especially  if  hot  and  dilute, 
reacts  on  any  calcium  sulphide  present,  forming  some  sodium  sulphide ; 
moreover,  moist  calcium  sulphide  oxidizes  rapidly  to  sulphate  in  the 
air,  and  this  reacts  with  the  sodium  carbonate.  Hence  the 'lixivia- 
tion must  be  done  as  rapidly  as  possible,  at  a  low  temperature,  and 
without  exposing  the  wet  black-ash  to  the  air. 

Shank's  process  gives  the  most  satisfactory  results.  The  lixivia- 
tion is  carried  on  in  a  series  of  tanks,  each  having  a  false  bottom  per- 
forated with  small  holes.  Because  of  its  density,  the  solution  of 
sodium  carbonate  sinks,  and  passing  through  these  perforations,  is 
drawn  off  by  means  of  a  pipe  which  delivers  it  at  the  top  of  the  next 
tank.  There  must  always  be  sufficient  liquor  in  each  tank  to  keep 
the  black-ash  entirely  submerged.  The  process  is  continuous,  suffi- 
cient fresh  water  being  admitted  to  the  nearly  exhausted  ash  to  give 
an  unbroken  flow  of  strong  liquor  (above  45°  Tw.)  from  the  last  tank 
of  the  series.  When  the  liquor  from  the  last  tank  falls  to  45°  Tw.,  it 
is  turned  into  a  tank  which  has  just  been  filled  with  new  ash.  The 
exhausted  ash  is  washed  until  the  wash  water  has  a  density  of  only 
1°  Tw.  Then  the  residue  of  calcium  sulphide  and  hydroxide,  coal, 
ashes,  and  other  insoluble  matter,  which  constitutes  the  "  tank  waste," 
is  dumped  and  the  tank  refilled  with  black-ash  arid  made  the  last  of 
the  series,  to  receive  the  strong  liquors  from  the  preceding  tank. 
H 


98  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

Since  the  black-ash  contains  caustic  lime,  sufficient  heat  is  gen- 
erated by  its  slaking  during  the  lixiviation  to  warm  the  concentrated 
liquor  to  about  50°  C.,  which  is  the  best  temperature  for  complete  ex- 
traction. The  temperature  of  the  dilute  lye  from  the  first  tank  of 
the  series  is  not  allowed  to  rise  above  38°  C.,  in  order  to  prevent  the 
above-mentioned  interaction  between  the  calcium  sulphide  and  the 
sodium  carbonate. 

Good  tank  liquor  has  approximately  the  following  composition :  — 

Na2CO3  (+NaOH)        23.60* 

NaCl 50 

Na^S 13 

NajSaO, 30 

Na*SO4 23 

Na2SiO3  ) 

NaCN  Traces. 

NaCNS 

FeS  (in  solution)  J 

The  lye  obtained  by  the  lixiviation  has  a  specific  gravity  of  about 
1.25,  and  is  muddy  from  suspended  impurities.  It  is  purified  by 
settling  and  then  pumped  to  the  top  of  the  "  carbonating  towers," 
which  are  filled  with  pebbles  or  coke,  or  have  numerous  chains  or 
wire  ropes  suspended  from  the  top  and  weighted  at  the  lower  ends. 
The  tank  liquor  trickles  over  the  porous  material  or  chains,  and 
comes  into  intimate  contact  with  a  strong  current  of  carbon  dioxide  f 
entering  at  the  bottom  and  passing  up  through  the  tower. 

The  carbon  dioxide  and  oxygen  which  pass  through  the  tower 
convert  the  caustic  soda  to  carbonate,  decompose  the  ferro-sodium 
sulphide  (solution  of  ferrous  sulphide  in  sodium  sulphide),  convert- 
ing the  sodium  sulphide  into  bicarbonate,  and  precipitating  the  iron, 
together  with  any  silica  and  alumina  which  may  be  present. 

The  reactions  involved  were  supposed  to  be  the  following :  — 

1)  2  NaOH  +  CO2  =  Na2CO3  +  H2O. 

2)  Na2S  +  C02  +  H20  =  NaHCO3  +  NaSH. 

3)  NaHCO3  +  NaSH  =  Na2CO3  +  H2S. 

Reactions  (2)  and  (3)  are  incomplete,  as  hydrogen  sulphide  is  of 
practically  the  same  acid  strength  as  carbonic  acid ;  only  when 

*  Mohr,  Analysis  of  Soda-ash  from  Stolberg  (Lunge,  Sulphuric  Acid  and  Alkali, 
Vol.  II). 

t  This  is  derived  from  the  gases  of  the  black-ash  furnace,  which  also  contain 
some  oxygen.  Or  it  is  obtained  from  the  gases  from  lime  kilns,  which  are  much 
richer  in  carbon  dioxide  and  introduce  less  flue  dust  into  the  product. 


THE    SODA   INDUSTRIES  99 

enough  CO2  is  used  to  convert  all  the  carbonate  to  bicarbonate,  or 
when  a  large  excess  is  used  at  fairly  high  temperature,  can  all  the  sul- 
phide be  decomposed.  By  adding  zinc  hydroxide  the  sulphide  may 
be  precipitated  :  — 

Na2S  +  Zn(OH)2  =  ZnS  +  2  NaOH. 

Or  by  blowing  air  through  the  tank  liquor  the  sulphide  is  converted 
to  thiosulphate  :  — 

NmS  +  2  O2  +  H2O  =  2  NaOH  +  Na«SA. 

Pauli's  process  of  purifying  tank  liquor  by  adding  "  Weldon  mud  " 
and  blowing  in  air  and  steam  is  more  effective.  Thus  the  sulphide  is 
oxidized,  and  ferric  oxide,  alumina,  and  silica  precipitate  in  the  sludge. 
Assuming  "  Weldon  mud  "  to  be  essentially  manganese  dioxide,  the 
following  reactions  take  place  :  — 


2  Na^S  +  4  Mn02  +  5  H2O  =  2  NaOH  +  NasSA  +  Mn(OH)2. 
Mn(OH)2  +  2  02  =  4  MnO2  +  4  H2O. 

The  manganese  oxide  thus  recovered  is  used  repeatedly,  until  it  be- 
comes much  contaminated  with  ferric  oxide,  alumina,  silica,  etc. 

After  settling,  the  purified  and  carbonated  tank  liquor  is  drawn 
into  the  evaporating  pans,  usually  large  shallow  iron  tanks,  and  heated 
by  surface  contact  with  the  waste  gases  from  the  black-ash  furnace. 
Sometimes  deep  pans,  heated  from  below,  are  used,  since  surface 
evaporation  gives  a  product  contaminated  with  dust  from  the  furnace. 
The  liquor  is  evaporated  directly  to  dry  ness,  and  the  "  black  salt  " 
(chiefly  monohydrated  sodium  carbonate,  Na2COs  •  H2O)  is  calcined 
by  heating  it  to  a  red  heat.  Sometimes  sawdust  is  mixed  with  the 
uncarbonated  liquor  before  evaporation,  and  then  on  calcining,  the 
soda-ash  is  carbonated  by  the  carbonaceous  matter  from  the  wood  ; 
but  the  charge  is  liable  to  cake  in  this  method.  The  caustic  soda  and 
sodium  sulphide  of  the  tank  liquor  are  thus  converted  to  sodium  car- 
bonate, and,  after  the  sawdust  is  burned  out,  the  ash  becomes  white 
or  light  brown. 

Or  the  liquor  is  evaporated  till  a  crystalline  mass  separates  ;  then 
the  mother-liquor  ("  red  liquor  ")  is  drawn  off,  and  the  black  salt  is 
raked  out  of  the  pan.  Much  care  is  necessary  to  prevent  the  forma- 
tion of  a  crust  or  the  burning  on  of  the  precipitated  carbonate. 

In  large  works,  a  semi-cylindrical  evaporating  pan  is  used, 
provided  with  mechanical  scrapers,  to  prevent  the  black  salt  from 
adhering  to  the  pan.  An  excellent  form  of  this  apparatus  is 


100 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


Thelen's  pan  (Fig.  48).  In  this,  the  scrapers  (R,  R)  move  the  salts 
towards  the  end  of  the  pan  as  they  deposit,  and  a  scoop  lifts  them  to 
the  draining  apron.  The  beam  (B),  carrying  the  frame  from  which 
the  scrapers  are  suspended,  is  rotated  by  the  gear  (J). 


For  a  very  light-colored  product,  the  crude  soda-ash  is  dissolved 
in  water,  and  a  little  bleaching  powder  solution  added ;  the  precipi- 
tated iron  and  other  impurities  settle  out,  and  the  clear  solution  is 
evaporated  until  a  thick  mass  of  crystals  separates,  when  the  mother- 
liquor  is  drawn  off  to  remove  any  soluble  impurities.  The  mono- 
hydrated  salt  remaining  is  then  calcined  without  the  addition  of  car- 
bonaceous matter,  to  remove  its  crystal  water,  and  the  product  is 
called  "  white  alkali  "  or  "  refined  alkali."  A  little  sodium  chloride 
is  formed  by  the  addition  of  the  bleaching  powder,  so  that  refined 
alkali  is  not  quite  so  strong  as  soda-ash.  It  is  chiefly  used  for  glass 
making  and  other  purposes  where  iron  and  sulphides  would  be  detri- 
mental. Good  Leblanc  soda  is  nearly  white  or  pale  yellow,  and  should 
contain  but  few  black  specks.  It  usually  contains  a  little  caustic 
soda,  a  trace  of  sulphides  and  sulphites,  some  chloride  and  sulphate, 
and  not  over  1  per  cent  of  insoluble  matter.  It  should  be  finely 
ground  before  packing. 

Soda  crystals  or  sal-soda  (Na2CO3  •  10  H2O)  is  made  by  dissolving 
soda-ash  in  warm  water,  allowing  the  hot  solution  to  stand  quietly 
until  all  sediment  deposits,  and  drawing  off  the  clarified  liquor  into 
crystallizing  tanks,  where  is  it  cooled  to  the  atmospheric  temperature. 
Large  crystals  of  sal-soda,  very  nearly  pure,  are  deposited.  They 
contain  over  60  per  cent  of  water,  and  are  thus  very  bulky  and  not 
economical  to  ship ;  but  they  are  still  preferred  to  soda-ash  for  some 
manufacturing  purposes  and  for  household  uses.  They  are  some- 
times used  for  making  sodium  bicarbonate,  by  exposing  them  on  a 
grating  to  an  atmosphere  of  carbon  dioxide :  — 

Na2CO3  •  10  H2O  +  CO2  =  2  NaHCO3  +  9  H2O. 


THE    SODA   INDUSTRIES  101 

The  water  resulting  from  the  "reaction  drips  through,  leaving 
the  bicarbonate  on  the  grating. 

CAUSTIC  SODA 

Caustic  soda  is  made  from  soda-ash,  or  from  the  "  tank  liquors  " 
directly,  by  adding  calcium  hydroxide  (milk  of  lime)  to  the  solution  :  — 

Na2CO3  +  Ca(OH)2  =  CaCO3  +  2  NaOH. 

When  caustic  soda  is  the  ultimate  product,  it  is  generally  custom- 
ary to  use  this  lime  mud  (CaCO3)  instead  of  limestone,  in  the  charge 
for  the  black-ash  furnace,  for  the  formation  of  caustic  in  the  tank 
liquor  is  then  of  course  not  objectionable. 

The  tank  liquor  must  not  have  a  density  of  over  20°  Tw.  (1.10 
sp.  gr.),  or  the  reaction  will  be  incomplete.*  Consequently  it  is 
diluted  with  the  wash  waters  from  the  lime  mud  of  a  previous  opera- 
tion. The  liquor  is  then  heated  to  boiling,  and  run  into  large  iron 
tanks,  where  the  "  milk  of  lime  "  is  added,  and  the  mixture  well 
stirred.  Air  or  steam  is  usually  blown  into  the  liquor  to  assist  in  the 
mixing.  The  air,  especially  when  aided  by  the  addition  of  "  Weldon 
mud  "  (p.  118),  converts  the  sodium  sulphide  to  sodium  thiosulphate 
and  sulphate  :  — 

2  NajS  +  H2O  +  4  O  =  2  NaOH  + 


The  thiosulphate  is  afterwards  destroyed  by  oxidizing  it  to  the 
sulphate. 

*  This  reaction  may  be  written  in  the  ionic  form,  thus  :  — 
COr-  +  Ca(OH)2±2  OH-+  CaCO3. 


—  — 

Equilibrium  will  therefore  correspond  to  the  equation,  -  -  -    -   =  Const.,   where 

(OH-)2 

the  parenthesis  indicates  that  the  concentration  of  the  ion  enclosed  is  meant.  It  is 
desired  to  produce  a  high  hydroxyl  concentration  relative  to  the  carbonate,  but  this 
is  attained  only  at  low  total  concentration,  since  the  influence  of  the  hydroxyl  ion 
tending  to  reverse  the  reaction  is  proportional  to  the  square  of  its  concentration  while 
the  carbonate  is  only  in  the  first  power.  In  fact  in  dilute  solutions  the  reaction  goes 
almost  quantitatively  to  the  right,  but  at  20°  Tw.  the  conversion  is  only  about  85 
per  cent,  and  at  higher  concentrations  it  is  even  less.  These  facts  have  been  used  as 
text-book  illustration  of  the  industrial  application  of  the  law  of  mass  action,  but  it  is 
not  the  incompleteness  of  the  conversion  which  is  the  reason  for  the  technical  use  of 
dilute  solutions,  since  any  unconverted  carbonate  is  recovered  on  concentrating. 
It  is  rather  the  fact  that  the  precipitated  carbonate  requires,  in  any  case,  large 
amounts  of  water  for  washing,  which  must  be  evaporated.  Since  this  water,  if 
used  in  the  original  batch,  gives  the  advantage  of  high  causticization,  with  no  dis- 
advantages, it  is  of  course  employed. 


102  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

In  large  plants,  the  dilute  caustic  solution,  after  settling,  is  con- 
centrated in  multiple-effect  systems  to  a  density  of  60°  Tw.,  at  which 
point  the  other  salts,  such  as  sodium  carbonate  or  chloride,  still  dis- 
solved in  the  liquor,  begin  to  crystallize ;  the  liquor  is  then  run  into 
cast-iron  kettles  ("  pots  "),  which  are  heated  by  direct  fire,  and  the 
last  of  the  water  evaporated,  when  caustic  soda  remains  as  a  fused 
mass.  The  salts  separated  during  the  evaporation  are  raked  out. 
Some  nitre  may  be  added,  or  air  blown  in,  to  complete  the  oxidation 
of  any  thiosulphate  to  normal  sulphate,  which  remains  in  the  caustic, 
reducing  its  strength.  In  small  works  the  dilute  liquor  is  evaporated 
directly  in  the  iron  pots.  For  strong  caustic  zinc  oxide  is  often  added 
to  remove  the  sulphide  from  the  tank  liquors.  The  precipitated  zinc 
sulphide  is  removed  by  settling  and  calcined  to  reconvert  it  into 
oxide. 

The  fused  caustic  soda  is  run  directly  into  the  sheet-iron  drums 
in  which  it  is  sold.  These  are  sealed  as  soon  as  cold,  to  prevent  the 
absorption  of  moisture  by  the  caustic. 

Loewig's  process  *  for  caustic  soda  depends  on  the  formation  of 
sodium  ferrate  (Na2Fe2O4),  which  is  then  decomposed  with  water. 
The  soda  liquors  are  mixed  with  ferric  oxide,  and  the  mass  evaporated 
to  dryness  and  calcined  at  a  bright  red  heat,  usually  in  a  revolving 
furnace.  By  the  calcination,  a  reaction  between  the  sodium  carbonate 
and  the  iron  oxide  is  brought  about,  carbon  dioxide  escaping  and 
sodium  ferrate  remaining  in  the  furnace.  The  mass  is  washed  with 
cold  water  until  all  soluble  matter  is  removed ;  then  water  at  90°  C. 
is  run  over  the  sodium  ferrate,  by  which  it  is  decomposed,  caustic 
soda  formed,  and  iron  oxide  regenerated ;  the  last  is  returned  to  the 
calcining  process.  The  ferric  oxide  used  is  a  natural  iron  ore,  very 
clean  and  free  from  silica  or  other  impurities ;  that  made  by  calcining 
a  precipitated  ferric  hydroxide  is  not  well  adapted  to  the  process,  as 
it  gives  a  product  difficult  to  lixiviate.  The  density  of  the  resulting 
solution  of  caustic  is  about  62°  Tw.  (1.31  sp.  gr.),  and  so  less  evapora- 
tion is  necessary  than  in  the  lime  process,  where  the  density  is  only 
15°  or  20°  Tw.  Moreover,  there  are  no  other  salts  present,  such  as 
sulphate,  thiosulphate,  sulphide,  or  chloride,  and  the  product  is  purer 
than  that  yielded  by  the  lime  process.  But  Loewig's  process  is  not 
so  well  adapted  to  use  with  the  Leblanc  soda-ash,  because  the  tank 
liquors  must  be  evaporated  to  dryness  before  calcining  the  ferric  oxide 
and  sodium  carbonate  mixture,  and  the  sodium  carbonate  must  be 

*  German  Patent,  No.  1650,  Dec.  21,  1877.  J.  Soc.  Chem.  Ind.,  1887,  438. 
Konrad  W.  Jurisch,  Die  Fabrikation  von  Schwefelsaurer  Thonerde,  p.  13. 


THE    SODA    INDUSTRIES 


103 


pure.  The  process  may  be  advantageously  used  with  ammonia  soda- 
ash,  since  this  is  obtained  directly  as  a  solid  and  no  evaporation  is 
necessary. 

Caustic  soda  of  better  quality  can  be  made  by  Loewig's  method, 
but  it  cannot  be  made  so  cheaply  as  by  the  use  of  lime  with  the  tank 
liquor  of  the  Leblanc  process,  especially  in  small  works  where  the  out- 
put is  irregular  and  uncertain.  For  although  there  is  no  expense  for 
lime,  and  less  fuel  is  used  for  evaporation  in  the  former  method,  yet 
an  extensive  and  somewhat  costly  plant,  designed  to  reduce  labor  to 
the  minimum,  is  required,  and  considerable  fuel  is  needed  for  the 
calcination. 

For  the  preparation  of  caustic  soda  by  electrolysis  of  brine,  see 
p.  124. 

TREATMENT  OF  TANK  WASTE 

In  the  Leblanc  process  nearly  all  the  sulphur  of  the  salt-cake  re- 
mains in  the  "  tank  waste  "  or  residue  from  the  lixiviation  of  the  black- 
ash.  The  average  composition  of  this  waste  is  shown  in  the  follow- 
ing tables :  — 

COMPOSITION   OF   TANK  WASTE 

FRESH* 


REVOLVER 

HAND  FURNACE 

HAND  FURNACE 

Water 

29  20 

29  96 

3040 

Na2CO3     .... 

3  16 

1  97 

1.63 

CaCO3       

21.19 

36.92 

38.81' 

Ca(OH)2   .     .     . 

Trace 

885 

9.53 

CaS       

5689 

37.90 

35.12 

CaS2O3 

1  07 

068 

1.49 

CaSO3 

Trace 

CaSO4 

Trapft 

0  20 

CaSiO3      .     .               .     . 

3  53 

1  34 

1.21 

Coal      -     .. 

720 

7.04 

6.27 

A12O3    . 

1  02 

037 

0.13 

FeS       

1  65 

2.44 

2.76 

Sand     /, 

2.82 

1.79 

2.61 

*  Chance,  J.  Soc.  Chem.  Ind.,  1882,  p.  266. 


104 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


COMPOSITION   OF   WEATHERED   TANK   WASTE 
60  YEARS  OLD* 


w 

19  INCHES  BELOW  THE 
SURFACE 

5  FEET  BELOW  THE 
SURFACE 

CaCOs 

53  14 

5277 

CaSO4    

1787 

11  11 

CaSO3 

0  65 

3  10 

CaS2O3  

080 

289 

Pa^l 

O  C\A 

Insoluble  in  HC1      .... 

10  10 

1091 

A12O3,  Fe2O3,  etc  

7.18 

11  04 

Water    . 

10.26 

8.14 

When  fresh  waste  is  thrown  on  the  dump,  the  changes  produced 
by  weathering  cause  great  nuisance.  The  air  is  contaminated  by  the 
hydrogen  sulphide  and  sulphur  dioxide  liberated,  and  the  soluble 
polysulphides  of  calcium  and  sodium  formed  are  dissolved  by  rain- 
water, making  the  objectionable  "  yellow  liquors,"  which  run  into 
streams  and  sewers. 

In  fresh  waste  the  sulphur  is  chiefly  in  the  form  of  sulphide  and 
thiosulphate  of  calcium,  but  in  weathered  material  these  have  been 
converted  by  oxidation  into  sulphate  and  sulphite,  which  in  them- 
selves cause  no  trouble  except  by  their  bulk. 

The  simplest  method  of  disposing  of  waste  is  to  send  it  out  to  sea 
and  dump  it,  if  the  works  are  so  situated  that  this  is  convenient ;  or, 
if  this  is  impossible,  to  spread  it  evenly  and  beat  it  down  hard  to 
prevent  as  far  as  possible  the  infiltration  of  rain.  But  since  the  sul- 
phur thus  lost  every  year  represents  an  enormous  money  value,  many 
attempts  have  been  made  to  recover  it  in  an  available  form.  Of  the 
numerous  processes  proposed  only  three  need  be  considered  here. 

In  Mond's  process  the  waste  was  treated  directly  in  the  lixiviating  tanks  by 
blowing  air  or  chimney  gases  through  the  wet  mass.  This  oxidized  the  waste 
according  to  the  following  reactions :  — 

1)  CaS  +  2  H2O  =  Ca(SH)2  +  Ca(OH)2. 

2)  Ca(SH)2  +  4  O  =  CaS2O3  +  H2O. 

But  the  hydration  and  oxidation  processes  were  slow,  and  after  a  time  it  was 
necessary  to  lixiviate  the  mass,  blow  in  air,  and  again  lixiviate.  By  several  lixivia- 
tions  the  calcium  sulphydrate  and  thiosulphate  were  dissolved,  forming  "  yellow 


*  Lunge,  Sulphuric  Acid  and  Alkali,  2d  ed.,  Vol.  II,  p.  815. 


THE    SODA   INDUSTRIES  105 

liquors."  To  recover  the  sulphur  these  were  treated  while  still  hot  with  dilute 
hydrochloric  acid,  the  following  reactions  *  taking  place  :  — 

3)  CaS2O3  +  2  HC1  =  CaCl2  +  H2O  +  SO2  +  S. 

4)  Ca(SH)2  +  2  HC1  =  CaCl2  +  2  H2S. 

In  the  presence  of  the  calcium  chloride  solution  the  two  gases,  sulphur  dioxide 
and  hydrogen  sulphide,  react  upon  each  other,  forming  water  and  free  sulphur :  — 

5)  2  H2S  +  SO2  =  2  H2O  +  3  S. 

The  hydration  and  oxidation  process  was  so  controlled  that  the  proportion  of 
thiosulphate  to  sulphydrate  yielded  one  molecule  of  sulphur  dioxide  to  two  mole- 
cules of  hydrogen  sulphide.  When  properly  worked  very  little  escape  of  hydrogen 
sulphide  occurred.  The  precipitated  sulphur  was  filtered  from  the  solution  of  cal- 
cium chloride  which  went  to  waste.  The  sulphur  was  then  refined. 

This  process  recovered  about  60  per  cent  of  the  total  sulphur,  but  it  consumed 
a  great  deal  of  hydrochloric  acid,  which  now  has  considerable  value,  and  some 
sulphur  was  lost,  owing  to  the  formation  of  sulphate  and  sulphite  of  calcium,  which, 
being  insoluble,  were  left  in  the  residue  after  lixiviation.  The  process  is  not  now  in 
use. 

Schaffner  and  Helbig's  f  process  depends  upon  the  reaction  between  magnesium 
chloride  and  calcium  sulphide  in  a  boiling  solution :  — 

1)  CaS  +  MgCl2  +  H2O  =  CaCl2  +  MgO  +  H2S. 

2)  MgO  +  CaCl2  +  CO2  =  CaCOs  +  MgCh. 

The  second  reaction  was  employed  to  recover  the  magnesium  chloride,  but  the 
calcium  carbonate  formed  was  too  impure  for  use  in  the  black-ash  furnace.  The 
hydrogen  sulphide  set  free  was  pure,  and  could  be  utilized  by  burning  it  with  air, 
and  conveying  the  resulting  sulphur  dioxide  into  the  lead  chambers  of  the  sulphuric 
acid  plant ;  or  the  sulphide  could  be  decomposed  with  sulphur  dioxide,  according 
to  the  method  given  above,  reaction  (5).  Lime-kiln  gases  were  used  for  the  carbon 
dioxide  in  reaction  (2) .  This  process  was  not  a  commercial  success. 

The  Chance-Glaus  process  {  appears  to  be  the  only  successful 
method  of  recovering  sulphur  on  a  large  scale,  and  even  this  has  not 
fully  realized  the  original  expectations  of  its  promoters.  The  reac- 
tions of  the  process  were  proposed  by  Gossage  in  1837,  but  although 
he  worked  on  the  idea  for  thirty  years,  and  spent  a  large  fortune  in 
experimenting,  he  failed  to  make  it  a  success. 

The  following  are  the  reactions  involved :  — 

1)  2  CaS  +  H20  +  CO2  =  CaCO3  +  Ca(SH)2. 

2)  Ca(SH)2  +  H20  +  CO2  =  CaCO3  +  2  H2S. 

3)  CaS  +  H2S  =  Ca(SH)2. 

A  carbon  dioxide  containing  at  least  30  per  cent  CO2  is  necessary 
and  is  obtained  in  a  special  form  of  lime  kiln.  The  tank  waste  is 

*  Mactear  proposed  to  use  the  same  reactions  for  the  treatment  of  the  drain- 
age from  old  waste  heaps,  which  were  creating  a  nuisance. 

t  J.  Soc.  Chem.  Ind.,  1882,  264.  J  Ibid.,  1888,  162. 


106 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


diluted  with  water  and  treated  by  counter-current  system,  with  the 
carbon  dioxide  gas,  in  a  series  of  seven  cast-iron  cylinders,  so  arranged 
that  one  may  be  emptied  and  recharged  while  the  others  are  in  un- 
interrupted operation.  Since  hydrogen  sulphide  and  carbon  dioxide 
are  acids  nearly  equal  in  strength,  no  hydrogen  sulphide  is  set  free 
till  the  calcium  sulphide  is  converted  to  a  mixture  of  calcium  sul- 
phydrate  and  bicarbonate.  The  gas  entering  a  freshly  filled  tank  is 
largely  hydrogen  sulphide  and  nitrogen ;  the  former  is  absorbed  as 
shown  in  reaction  (3),  while  nitrogen  escapes,  until  the  calcium  sul- 
phide is  nearly  all  converted  to  sulphydrate.  Reaction  (2)  then 
progresses  and  the  content  of  hydrogen  sulphide  in  the  gas  leaving 
the  tank  rises  rapidly  and  it  is  collected  in  a  gasometer.  As  the  treat- 
ment proceeds,  the  hydrogen  sulphide  content  of  the  gas  falls  off  while 
the  percentage  of  CO2  rises  correspondingly.  When  the  hydrogen 
sulphide  is  below  30  per  cent,  the  gases  are  diverted  to  a  freshly  filled 
tank,  where  reaction  (3)  takes  place. 

The  hydrogen  sulphide  collected  in  the  gasometer,  together  with 
air,  is  passed  through  the  Claus  sulphur  kiln  (Fig.  49),  in  which  the 
reaction  H2S  +  O  =  H2O  +  S 

takes  place.  On  the  grate  (A)  is  a  layer  of  broken  fire-brick  covered 
with  about  12  inches  of  ferric  oxide  to  serve  as  a  catalyzer  of  the  re- 
action. The  mixture  of  hydrogen  sulphide  and  air  is  led  into  the  kiln 

at  (B),  and  made 
to  pass  through  the 
ferric  oxide  (pre- 
viously heated  to 
a  dull  red) ;  this 
causes  the  reaction 
to  take  place,  and 
at  the  same  time 
the  heat  generated 
by  the  reaction  is 
sufficient  to  keep 
the  iron  oxide  at  the  proper  temperature,  after  being  once  well  started. 
Sulphur,  nitrogen,  and  water  vapor  escape  from  the  kiln.  The  sulphur 
vapor  condenses  in  the  chamber  (D)  as  liquid  sulphur,  and  in  (E)  as 
flowers  of  sulphur,  while  the  steam  and  nitrogen,  together  with  a 
small  quantity  of  sulphur  dioxide,  pass  on  to  a  condensing  tower, 
where  they  are  brought  into  contact  with  limestone  over  which  water 
is  dripping,  to  retain  the  sulphur  dioxide.  When  working  well,  this 


HiS+O 


FIG.  49. 


THE    SODA   INDUSTRIES  107 

process  recovers  about  85  per  cent  of  the  sulphur.  According  to 
Lunge,  the  form  of  the  kiln  has  been  recently  modified,  but  the  prin- 
ciple of  the  process  is  unchanged.  The  water  in  the  storage  gasom- 
eter is  usually  covered  with  a  layer  of  petroleum  oil,  to  prevent  the 
absorption  of  the  hydrogen  sulphide  by  the  water. 

The  process  is  not  very  lucrative  when  the  price  of  sulphur  is  low, 
but  since  it  reduces  the  nuisance  created  by  the  alkali  waste,  and 
yields  very  pure  sulphur,  a  number  of  English  firms  employ  it.  In 
1893,  over  30  plants  were  in  operation  in  England,  and  more  than 
35,000  tons  of  sulphur  recovered. 

For  the  Parnell  and  Simpson  *  process  for  utilizing  alkali  waste, 
seep.  111. 

THE  AMMONIA  SODA  PROCESS 

The  reactions  involved  in  the  ammonia  soda  process  were  dis- 
covered by  H.  G.  Dyar  and  J.  Hemming,  about  1838,  but  owing  to  the 
mechanical  difficulties,  its  practical  success  was  not  thoroughly  estab- 
lished until  1873.  In  1863,  Ernest  Solvay,  a  Belgian,  constructed  an 
apparatus  which  has  led  to  an  enormous  development  of  the  industry, 
by  which  one-half  of  the  world's  supply  of  soda  is  now  made.  Its 
advantages  lie  in  the  strength  and  purity  of  its  products  and  the  ab- 
sence of  troublesome  by-products,  such  as  "  tank  waste."  But  it 
does  not  yield  chlorine  nor  hydrochloric  acid,  all  the  former  going  to 
waste  as  calcium  chloride. 

The  ammonia  soda  process  depends  upon  the  fact  that  sodium 
bicarbonate  is  but  slightly  soluble  in  a  cold  ammoniacal  solution  of 
common  salt.  The  technical  success  of  the  process  depends  chiefly 
on  the  proper  regulation  of  the  temperature  during  the  precipitation, 
and  on  the  capacity  of  the  works  to  handle  large  quantities  of  gases 
and  liquids.  As  far  as  possible,  manual  labor  must  be  avoided,  and 
the  products  moved  and  treated  in  solution  or  in  suspension.  The 
reactions  are  as  follows  :  — 


1)  NaCl  +  NH3  +  H20  +  COz  =  NH4C1  +  NaHCO3. 

2)  2  NH4C1  +  Ca(OH)2  =  CaCl2  +  2  H2O  +  2  NH3. 

The  first  equation  is  the  chief  one  ;  the  second  represents  the  recovery 
of  the  ammonia,  and  is  essential  to  the  commercial  success  of  the 
process. 

The  salt  is  used  as  a  very  concentrated  brine,  which  has  been 

*  J.  Soc.  Chem.  Ind.,  1889,  11. 


108 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


purified  from  iron,  silica,  magnesia,  etc. ;  it  is  then  saturated  with 
ammonia  gas,  obtained  from  gas  liquors,  or  by  the  recovery  process 
according  to  equation  (2).  The  carbon  dioxide  is  obtained  partly 
from  lime  kilns  and  partly  from  the  calcination  of  the  bicarbonate 
to  form  the  normal  carbonate  (p.  110).  It  must  contain  at  least  30 
per  cent  of  CC>2,  and  is  prepared  in  special  forms  of  continuous  lime 
kilns.  The  lime  resulting  is  used  in  the  recovery  of  the  ammonia 
(reaction  2),  and  for  making  caustic  soda ;  the  lime-kiln  gases  are 
cooled,  and  the  sulphur  dioxide  removed,  by  washing  in  water  before 
they  pass  into  the  carbonating  towers  (see  below). 

The  brine  is  contained  in  a  tank,  under  the  perforated  bottom  of 
which  the  ammonia  gas  is  introduced,  and  rising  through  the  liquor, 

is  rapidly  absorbed.  The 
heat  evolved  by  the  absorp- 
tion is  taken  up  by  cold 
water  circulating  in  coils. 
When  saturated,  the  am- 
moniacal  brine  is  pumped 
into  a  receiving  and  settling 
tank,  from  which  it  is  de- 
livered to  the  "  carbonating 
tower"  (Fig.  50).*  This  is 
from  50  to  65  feet  high,  built 
of  cast-iron  rings  or  seg- 
ments (A,  A),  each  about 
3.5  feet  high  and  6  feet  in 
diameter.  At  the  bottom  of 
each  segment  is  a  flat  plate 
having  a  large  hole  in  the 
centre.  Above  each  plate 
is  a  dome-shaped  diaphragm 
(D)  perforated  with  a  great 
number  of  small  holes.  In 
modern  works  a  system  of 
pipes  passes  through  each  segment,  as  shown  at  (B,  B) ;  in  these,  cold 
water  is  kept  flowing,  thus  counteracting  the  heat  generated  by  the 
chemical  action.  The  ammoniacal  brine  is  forced  under  pressure 
through  the  pipe  (P),  entering  a  little  above  the  middle  of  the  tower, 
which  is  nearly  filled  with  brine.  By  this  arrangement,  any  free 
ammonia  in  the  brine,  which  would  be  swept  away  by  the  stream  of 


FIG.  50. 


*  After  Lunge. 


THE    SODA   INDUSTRIES  109 

gases  passing  up  through  the  tower,  is  taken  up  by  the  carbon  dioxide 
in  the  upper  part  of  the  tower.  The  carbon  dioxide,  having  been  pre- 
viously well  cooled,  is  forced  through  the  pipe  (C),  entering  under  the 
lowest  dome,  and  rising  in  small  bubbles  through  the  perforations  in 
each  dome,  comes  into  intimate  contact  with  the  ammoniacal  brine. 
The  bicarbonate  of  sodium  thus  precipitated  gradually  works  its  way 
down  through  the  tower.  A  thick,  milky  liquid,  containing  the  bicar- 
bonate in  suspension,  and  ammonium  chloride  and  common  salt  in 
solution,  is  drawn  off  through  (H)  at  the  bottom. 

After  a  tower  has  been  in  use  for  some  days,  the  holes  in  the 
domes  become  clogged  with  a  deposit  of  bicarbonate  crystals,  which 
prevent  the  free  passage  of  the  gases.  Consequently,  every  ten  days 
or  two  weeks  the  liquid  must  be  drawn  out  and  the  crystals  dissolved 
by  filling  the  tower  with  hot  water  or  steam.  The  tower  must  be 
cooled  before  starting  the  process  anew.  As  a  rule,  several  towers 
are  employed,  so  that  one  may  be  cleaned  and  cooled  without  inter- 
rupting the  operation. 

The  gases  escaping  from  the  top  of  the  tower,  consisting  princi- 
pally of  nitrogen,  carbon  dioxide,  and  some  ammonia,  are  passed 
through  scrubbers  (p.  319),  one  of  which  contains  brine,  which  after- 
wards goes  to  the  ammonia  saturating  tank;  in  the  other  is  dilute 
sulphuric  acid,  to  absorb  the  small  amount  of  ammonia  which  would 
otherwise  be  lost.  The  carbon  dioxide  and  nitrogen  are  allowed  to 
escape.  The  towers  are  run  with  the  view  to  the  utilization  of  all 
the  ammonia  possible,  even  though  there  is  considerable  loss  of  salt 
and  carbon  dioxide;  usually  about  one-fourth  of  the  salt  remains 
undecomposed. 

It  is  now  customary  to  place  a  smaller  carbonating  tower  in  con- 
nection with  the  large  one;  in  the  former  the  brine  is  first  treated 
with  carbon  dioxide  and  the  ammonia  converted  to  neutral  carbonate 
(NH^COs;  then  the  brine  is  pumped  into  the  large  carbonating 
tower,  where  it  meets  more  carbon  dioxide,  and  the  bicarbonate  is 
formed,  causing  the  precipitation  of  the  sodium  bicarbonate.  More 
heat  is  liberated  in  the  formation  of  the  neutral  carbonate  of  am- 
monia than  in  its  conversion  to  the  bicarbonate,  hence  the  tempera- 
ture of  the  precipitation  is  more  easily  controlled  when  two  towers 
are  used,  and  less  free  ammonia  escapes  with  the  waste  gases. 

A  temperature  of  about  35°  C.  is  most  favorable  to  the  formation 
of  a  granular  or  crystalline  precipitate  of  bicarbonate,  and  also  to 
the  most  complete  utilization  of  the  ammonia.  At  higher  tempera- 
tures, too  much  bicarbonate  remains  dissolved  in  the  liquor;  at 


110  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

lower  temperatures,  there  is  a  tendency  to  the  crystallization  of  am- 
monium acid  carbonate  and  ammonium  chloride,  while  the  bicar- 
bonate separates  as  a  very  fine  precipitate,  which  is  difficult  to  filter 
from  the  liquor. 

The  milky  liquor  from  the  bottom  of  the  tower,  containing  the 
sodium  bicarbonate  in  suspension,  is  filtered  on  sand  filters  (p.  19) 
connected  with  a  vacuum  pump ;  or  better,  it  is  run  into  centrifugal 
machines  (p.  18),  which  afford  more  rapid  and  complete  separation 
of  the  mother-liquor.  The  bicarbonate  is  then  washed  with  water, 
to  remove  as  much  of  the  sodium  and  ammonium  chlorides  as  possible. 
The  mother-liquors  and  wash  waters  go  to  the  ammonia  recovery 
process. 

The  sodium  bicarbonate  is  then  calcined  in  large  covered  cast-iron 
pans  or  ovens ;  this  converts  the  acid  salt  into  soda-ash,  and  drives 
out  any  ammonia  or  moisture  still  in  the  mass.  The  following  is 
the  reaction :  — 

2  NaHCQs  =  Na2CO3  +  C02  +  H2O. 

The  fumes  are  passed  through  coolers  and  scrubbers  to  remove 
ammonia;  the  concentrated  carbon  dioxide  remaining  is  pumped 
into  the  carbonating  towers.  The  ammonia  liquors  go  to  the  ammonia 
stills. 

A  modification  of  the  Thelen  pan  (Fig.  48,  p.  100)  is  sometimes 
used  for  this  calcining.  A  gas-tight  cover  is  placed  over  the  pan, 
and  the  scrapers  pass  back  and  forth  over  the  pan  bottom,  being 
moved  by  a  connecting  rod  and  crank.  The  gases  and  steam  pass 
off  through  a  pipe  set  in  the  cover.  In  practice,  it  has  been  found 
best  to  leave  the  mass  in  this  pan  only  until  all  the  ammonia  and 
about  75  per  cent  of  the  carbon  dioxide  of  the  bicarbonate  have  been 
expelled ;  the  calcination  is  completed  in  a  reverberatory  furnace. 

The  product  of  the  calcination  is  called  soda-ash ;  it  is  often  very 
pure,  containing  only  a  trace  of  salt  and  a  little  bicarbonate,  and  is 
free  from  caustic  soda,  sulphide,  and  sulphate.  But  its  density  is 
only  0.8,  while  that  of  the  Leblanc  product  is  1.2.  This  is  disad- 
vantageous, owing  to  the  larger  packages  needed  for  a  given  weight 
and  to  the  mechanical  loss  incurred  in  operations  where  the  soda-ash 
is  exposed  to  a  strong  draught  of  air.  In  order  to  increase  the  den- 
sity, it  is  sometimes  subjected  to  a  second  heating  in  a  reverberatory 
(revolving)  furnace. 

The  second  reaction,  on  p.  107,  is  that  on  which  the  recovery  of 
the  ammonia  depends.  The  liquid  in  which  the  bicarbonate  of  soda 


THE    SODA    INDUSTRIES  111 

was  suspended  contains  undecomposed  salt,  ammonium  chloride,  and 
ammonium  carbonate.  It  is  passed  through  an  ammonia  still,  usually 
a  tall  column  or  dephlegmator  (p.  11).  Steam  is  admitted  at  the 
bottom  of  the  apparatus,  and  bubbling  up  through  the  liquid,  de- 
composes the  ammonium  carbonate  into  ammonia,  carbon  dioxide, 
and  water ;  the  ammonium  chloride  passes  down  into  the  lower  part 
of  the  tower,  or  the  still  proper,  where  it  is  decomposed  by  "  milk  of 
lime."  The  ammonia  set  free  is  cooled  and  used  to  saturate  the 
brine.  The  calcium  chloride  formed  remains  in  solution,  and  together 
with  the  excess  of  salt,  goes  to  waste.  Some  calcium  chloride  is  re- 
covered and  finds  use  as  a  dust-layer  and  binder,  on  macadam  and 
dirt  roads.  (For  various  proposals  to  utilize  the  waste  calcium  chloride 
for  the  production  of  hydrochloric  acid  and  chlorine,  see  p.  122.) 

The  damp  bicarbonate  is  dried  in  an  atmosphere  of  carbon  dioxide, 
at  a  temperature  of  about  90°  C. ;  this  prevents  decomposition  of  the 
sodium  bicarbonate,  while  the  ammonium  bicarbonate  is  decomposed, 
the  vapors  passing  to  the  scrubbers,  where  the  ammonia  is  recovered. 
A  considerable  quantity  of  the  bicarbonate  of  soda  is  sold  directly 
to  the  manufacturers  of  baking  Dowder  and  the  poorer  grades  to  the 
soda-water  makers. 

Caustic  soda  can  be  made  stronger  and  purer  from  ammonia  soda- 
ash  than  from  Leblanc  ash,  and  the  process  is  not  essentially  differ- 
ent, except  that  no  treatment  to  remove  sulphur  is  necessary ;  but  it 
cannot  be  made  so  cheaply  as  from  the  "  red  liquors  "  or  the  "  tank 
liquors  "  of  the  Leblanc  process.  If  pure  lime  is  used  for  causticiz- 
ing  ammonia  soda-a?h,  the  product  is  better  than  in  the  case  of  the 
Leblanc  ash,  as  it  is  free  from  sulphur,  alumina,  etc. 

Loewig's  process  (p.  102)  appears  especially  suited  for  causticiz- 
ing  ammonia  soda-ash,  since  it  requires  an  ash  free  from  silica. 

H.  A.  Frasch  devised  a  method  for  caustic  soda  in  which  nickel 
hydroxide  acts  upon  sodium  chloride  in  the  presence  of  an  excess  of  am- 
monia. A  double  nickel-ammonium  chloride  [Ni(NH3)2Cl2  +  4  NHs] 
separates  as  a  violet  crystalline  mass,  leaving  caustic  soda  in  the 
solution.  This  double  salt  is  hygroscopic,  dissolves  with  a  blue  color, 
and  evolves  some  ammonia.  The  nickel  and  ammonia  may  be  re- 
covered by  treating  the  salt  with  milk  of  lime. 

The  Parnell  and  Simpson  process  *  was  expected  to  solve  the 
problem  of  the  Leblanc  "  alkali  waste,"  but  it  has  not  fulfilled  the 
hopes  of  its  promoters.  It  was  proposed  to  work  the  two  leading 
soda  processes  in  combination.  The  alkali  waste  of  the  Leblanc 

*  J.  Soc.  Chem.  Ind.,  1889,  11. 


112  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

process  is  boiled  in  the  ammonium  chloride  liquor  from  the  ammonia 
process,  and  the  vapors  of  ammonia  gas  and  of  ammonium  sulphide 
liberated  are  led  directly  into  a  brine  solution  in  the  saturating  tank. 
The  calcium  chloride  liquor  goes  to  waste.  The  ammoniacal  solution 
of  brine  and  ammonium  sulphide  produced  is  sent  to  a  carbonating 
tower,  similar  to  that  described  on  p.  108,  and  treated  with  carbon 
dioxide,  as  in  the  ammonia-soda  process.  Sodium  bicarbonate  is  pre- 
cipitated and  hydrogen  sulphide  set  free,  which  may  be  treated  in  a 
Claus  kiln  (p.  106),  or  burned  to  sulphur  dioxide  to  use  for  sulphuric 
acid.  The  reactions  involved  are  as  follows :  — 

1)  CaS  +  2  NEUCl  =  (NH4)2S  +  CaCl2.* 

2)  (NH4)2S  +  CO2  +  H2O  =  NH4HCO3  +  NHJIS. 

3)  NH4HS  +  C02  +  H20  =  NH4HCO3  +  H2S. 

4)  NH4HC03  +  NaCl  =  NaHCO3  +  NH4C1. 

The  last  three  reactions  take  place  f  simultaneously  in  the  carbonat- 
ing tower;  the  hydrogen  sulphide  generated  goes  to  the  sulphur  re- 
covery and  the  ammonium  chloride  solution  carrying  sodium  bicar- 
bonate in  suspension  is  drawn  out  and  filtered.  The  ammonium 
chloride  liquor  is  returned  to  the  process. 

The  conversion  of  salt  into  sodium  carbonate  by  any  method  in- 
volves an  endothermic  reaction  in  some  part  of  the  process.  Thus 
energy  must  be  expended,  necessitating  the  use  of  fuel.  In  the  Leblanc 
process,  the  fuel  expenditure  is  large  in  carrying  out  the  reactions  in 
the  salt-cake  and  the  black-ash  furnaces.  But  much  of  the  expended 
energy  reappears  in  the  hydrochloric  acid,  the  principal  by-product. 

In  the  ammonia  process  the  principal  reactions  are  exothermic, 
but  some  fuel  is  consumed  by  the  calcination  of  the  precipitated  bicar- 
bonate and  in  the  preparation  of  the  quicklime  used  in  the  ammonia 

*  Equation  (1)  does  not  exactly  represent  the  facts,  as  some  polysulphides  are 
present  in  the  tank  waste. 

t  According  to  Lunge,  Sulphuric  Acid  and  Alkali,  3d  ed.,  Vol.  Ill,  p.  204,  the 
sodium  bicarbonate  is  formed  by  agitating  the  brine  with  crystallized  ammonium 
bicarbonate,  the  latter  being  obtained  by  saturating  the  ammonium  sulphide  solu- 
tion with  carbon  dioxide.  The  carbon  dioxide,  which  must  be  very  pure  and  con- 
centrated, is  made  by  heating  ammonium  bicarbonate  crystals  to  74°  C.,  in  a  retort, 
CO2,  steam,  and  NHs  passing  off.  By  scrubbing  (p.  319),  the  carbon  dioxide  is  ob- 
tained pure. 

Ammonium  bicarbonate  is  also  prepared  by  passing  lime-kiln  gases  into  a  solu- 
tion of  ammonia  or  neutral  ammonium  carbonate,  and  then  cooling  it  to  crystallize 
the  bicarbonate. 


THE    SODA    INDUSTRIES  113 

recovery  and  for  generating  carbon  dioxide.  Although  less  fuel  is 
used  than  in  the  Leblanc  process,  the  practical  economy  of  the  am- 
monia process  is  not  so  great  as  would  at  first  appear ;  for  all  the 
chlorine  is  lost,  together  with  much  of  the  original  salt  used.  As  a 
method  for  soda-ash  it  is  far  superior  to  the  Leblanc,  but  until  a  prac- 
tical process  for  the  cheap  production  of  chlorine  is  discovered,  the 
latter  will  continue  to  be  an  extensive  industry. 

THE  CRYOLITE  SODA  PROCESS 

Cryolite  is  a  double  fluoride  of  sodium  and  aluminum,  found  as 
a  mineral  in  southern  Greenland.  As  no  other  important  deposit 
has  been  found,  the  supply  is  limited,  and  only  two  or  three  manu- 
factories using  this  process  were  established,  —  one  of  them  in  this 
country.  The  reactions  involved  are  as  follows :  — 

1)  A1F3  -  3  NaF  +  3  CaCO3  =  NaAlO2  +  Na2O  +  3  CaF2  +  3  CO2. 

2)  NaAlO2  +  Na2O  =  Na3AlO3. 

3)  2  Na3A103  +  3  H2O  +  3  CO2  =  3  Na2CO3  +  2  A1(OH)3. 

The  ground  cryolite  is  mixed  with  powdered  limestone,  and  calcined 
at  a  red  heat.  Carbon  dioxide  escapes,  and  a  mixture  of  calcium 
fluoride,  sodium  oxide,  and  sodium  aluminate  remains.  On  lixiviat- 
ing this  mixture  with  water,  another  sodium  aluminate  is  formed  and 
goes  into  solution,  leaving  the  calcium  fluoride  as  an  insoluble  resi- 
due. The  solution  of  sodium  aluminate  is  then  decomposed  according 
to  the  third  reaction,  by  passing  into  it  purified  lime-kiln  gases,  or 
the  furnace  gases  of  the  calcining  operation.  Hydrated  alumina  is 
precipitated,  while  sodium  carbonate  remains  in  solution.  Sal-soda 
may  be  made  by  evaporating  the  solution,  and  was  formerly  the  chief 
source  of  bicarbonate  for  culinary  and  medicinal  purposes.  If  carried 
to  complete  dryness  and  calcined,  a  high  grade  of  soda-ash  is  obtained. 
By  causticizing,  it  yields  a  very  excellent  caustic. 

The  by-products  aluminum  hydroxide  and  calcium  fluoride  are 
used  in  the  alum  and  glass  industries  respectively. 

Many  other  processes  for  the  manufacture  of  soda  from  salt  have 
been  proposed,  but  none  of  them  are  now  of  any  commercial  impor- 
tance. A  small  amount  of  soda  is  still  made  from  kelp  or  varec, 
which  is  the  ash  of  seaweeds. 

A  new  process  for  making  soda  has  been  proposed,*  which  is  in- 
teresting, but  has  not  as  yet  been  placed  on  a  practical  basis.  Salt- 

*  J.  Soc.  Chem.  Ind.,  1895,  933. 


114  OUTLINES   OF    INDUSTRIAL   CHEMISTRY 

cake  is  made  from  salt  by  the  Hargreaves  process  (p.  92) ;  then  in 
the  same  cylinder  and  at  the  same  temperature,  it  is  treated  with 
water  gas.  This  reduces  the  salt-cake  to  sodium  sulphide,  while  water, 
carbon  monoxide,  and  hydrogen  escape.  These  vapors  are  cooled,  the 
water  condensed,  and  the  mixture  of  gases  burned,  the  products  of 
combustion,  carbon  dioxide  and  water,  passing  into  the  cylinders  con- 
taining the  sodium  sulphide.  Hydrogen  sulphide  and  sodium  car- 
bonate are  formed,  and  as  the  temperature  is  much  above  100°  C.,  no 
water  can  combine  with  the  carbonate.  The  hydrogen  sulphide  is 
burned  to  sulphur  dioxide,  and  the  latter  returned  to  the  Hargreaves 
process.  The  reactions  involved  are  as  follows  :  — 

1)  2  NaCl  +  SO2  +  H2O  +  O  =  Na2SO^+  2  HC1. 

2)  NajSOfc.+  5  CO  +  5  H2  =  Na2S  +  4  H2O  +  5  CO  +  H2. 

3)  CO  +  H2  +  O2  =  CO2  +  H2O. 

4)  Na2S  +  C02  +  H20  =  Na2CO3  +  H2S. 

5)  H2S  +  3  O  =  H2O  +  SO2. 

This  process  seems  to  offer  several  advantages,  viz. :  — 

1.  Cheap  materials. 

2.  Small   outlay  for  labor,  —  the  materials   not   being   handled 
from  the  time  the  salt  is  charged  into  the  cylinders  until  the  soda- 
ash  is  raked  out. 

3.  No  waste  products  nor  nuisance. 

4.  The  temperature  constantly  decreases,  being  highest  when  the 
furnace  is  charged  and  lowest  when  the  soda-ash  is  finished. 

5.  The  process  yields  hydrochloric  acid  which  can  be  utilized. 
For  the  methods  of  producing  caustic  soda  and  chlorine  by  elec- 
trolysis of  brine,  see  Chlorine,  p.  124. 

REFERENCES 

Berichte  ueber  die  Entwickelung  der  chemischen  Industrie.     A.  W.  Hoff- 
mann, Vol.  I,  418.     (1875.) 

History,  Products,  and  Processes  of  the  Alkali  Trade.     Charles  T.  King- 
zett,  London,  1877.     (Longmans.) 

Manual  of  Alkali  Trade.     John  Lomas,  London.     (Crosby,  Lockwood  Co.) 

Die  Fabrikation  der  Soda  nach  dem  Ammoniak-Verfahren.     H.  Schreib, 
Berlin,  1905. 

Sulphuric  Acid  and  Alkali.     G.  Lunge,  3d  ed.,  Vols.  II,  1909,  III,  1911. 
(D.  Van  Nostrand  Co.,  New  York.) 

J.  Soc.  Chem.  Ind :  — 

1883,  405,   Walter  Weldon.     1885,   527,   Ludwig   Mond.     1886,   412, 

E.  K.  Muspratt. 

1887,  416,  Watson  Smith.     1888,  162,  Alexander  Chance.      1889,  11, 
E.  Parnell. 


CHLORINE   INDUSTRY 

Chlorine  is  extensively  used  in  the  arts  as  a  bleaching  and  oxidiz- 
ing agent.  It  is  chiefly  employed  in  the  form  of  a  solution  of  "  bleach- 
ing powder  "  or  "  chloride  of  lime,"  which  contains  calcium  hypo- 
chlorite,  and  as  chlorates  or  hypochlorites  of  the  alkali  metals.  Liquid 
chlorine,  compressed  in  steel  cylinders,  has  recently  become  an  article 
of  commerce,  and  this  form  of  shipment  may  be  extended  in  the  future. 

Practically  all  the  chlorine  used  in  the  arts  must  be  derived  from 
the  chlorides  of  sodium,  potassium,  or  magnesium,  which  are  found 
more  or  less  abundantly  in  nature.  A  large  part  of  the  hydrochloric 
acid  made  from  salt  (p.  88)  is  used  for  making  chlorine.  Since  this 
acid  is  the  chief  by-product  of  the  Leblanc  process,  a  plant  for  mak- 
ing bleaching  powder  is  always  a  part  of  those  works. 

The  important  methods  of  making  chlorine  from  the  acid  may 
be  considered  under  two  heads :  ':hose  using  manganese  oxides  for 
decomposing  the  acid,  and  those  not  using  manganese  for  this  purpose. 

The  function  of  manganese  is  to  oxidize  the  hydrogen  of  the  acid, 
forming  water  and  liberating  the  chlorine.  At  the  same  time,  the 
manganese  is  converted  into  chloride,  and  being  expensive,  its  recovery 
in  a  form  that  permits  of  its  return  to  the  process  is  essential. 

The  oxides  of  manganese  are  found  in  nature  as  pyrolusite  (MnO2), 
braunite  (Mn2O3),  manganite  (Mn2O3  •  H2O),  hausmannite  (Mn3O4), 
wad,  and  psilomelane,  the  last  two  of  indefinite  composition.  The 
reactions  occurring  when  manganese  oxides  are  treated  with  hydro- 
chloric acid  are  as  follows  :  — 

1)  MnO  +  2  HC1  =  MnCl2  +  H2O. 

2)  MnO2  +  4  HC1  =  MnCl2  +  2  H2O  +  2  Cl. 

3)  Mn203  +  6  HC1  =  2  MnCl2  +  3  H2O  +  2  CL 

4)  Mn3O4  +  8  HC1  =  3  MnCl2  +  4  H2O  +  2  Cl. 

Thus  it  is  readily  seen  that  with  pyrolusite,  less  acid  is  necessary 
for  a  given  yield  of  chlorine,  and  a  smaller  quantity  of  manganous 
chloride  must  be  treated  to  recover  the  manganese.  This  ore  is 
purchased  according  to  its, content  of  MnO2,  which  is  estimated  by 
determining  the  "  available  "  oxygen.  The  presence  of  iron  oxides, 
silica,  calcium  carbonate,  etc.,  is  disadvantageous. 

In  small  works,  especially  where  no  attempt  is  made  to  recover 
the  manganese,  the  process  is  carried  on  in  simple  stills  of  earthen- 

115 


116 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


FIG.  51. 


ware  or  sandstone.  The  earthenware  stills 
(Fig.  51)  *  are  cheap,  but  of  limited  capacity. 
They  are  heated  by  blowing  free  steam  into 
the  wooden  casing  in  which  they  are  set. 
The  pyrolusite  is  put  into  the  central  per- 
forated cylinder,  and  the  acid  runs  through 
the  pipe  (A),  chlorine  escaping  at  (B). 
Sandstone  stills  (Fig.  52)  *  are  made  from 
single  blocks  of  sandstone,  or  built  up  of 
slabs,  the  joints  being  made  tight  by  a 
rubber  packing,  or  by  a  lute  of  clay  and 
linseed  oil.  The  pyrolusite  rests  on  a  false 
bottom  (A),  and  the  acid  is  run  in  through  (B),  while  steam  is  blown 
in  through  the  sandstone  pipe  (C).  Chlorine  escapes  through  (D). 
These  stills  are 
larger  than  the 
earthenware  ones, 
but  do  not  utilize 
the  acid  so  com- 
pletely. 

The  chlorine  is 
conducted  through 
pipes  of  lead  or 
earthenware,  or 
tubes  coated  with 
bakelite  enamel.  Since  valves  in  these  pipes  are  rapidly  corroded, 
a  device  shown  in  Fig.  53  *  is  used  to  shut  off  the  flow  of  gas.  A 

U-shaped  bend  is  made  in  the  pipe,  and 
a  small  flexible  tube  attached  at  the  lowest 
point  of  the  U,  connecting  it  with  the 
vessel  (A),  filled  with  water.  By  raising 
(A),  the  water  flows  into  and  fills  the 
U-pipe  to  the  line  (CD),  cutting  off  the 
flow  of  gas.  By  lowering  (A)  to  (A')> 
the  water  runs  out  of  the  U,  and  the  flow 
of  gas  is  uninterrupted. 

The  liquor  remaining  in  the  still  con- 
tains much  free  acid,  manganous  chloride, 
ferric  chloride,  etc.  It  continues  to  evolve 
some  chlorine  for  a  long  time,  and  is  a 


FIG.  52. 


*  After  Lunge. 


CHLORINE    INDUSTRY 


117 


very  offensive  and  troublesome  material  to  dispose  of,  since  it  pol- 
lutes the  air,  or  the  streams,  into  which  it  passes. 

Of  the  many  attempts  to  recover  the  manganese,  the  two  follow- 
ing are  the  most  important :  — 

By  Dunlop's  method,  the  "  still  liquor  "  is  neutralized  cold,  with 
powdered  limestone,  until  all  free  acid  is  removed  and  the  iron  pre- 
cipitated. The  clear  solution  of  manganous  and  calcium  chlorides  is 
then  mixed  with  a  carefully  determined  quantity  of  powdered  lime- 
stone or  chalk,  and  heated  under  pressure  by  steam.  This  precipi- 
tates the  manganese  as  carbonate,  which  is  settled,  and  the  solution 
of  calcium  chloride  drawn  off.  The  manganous  carbonate  is  washed 
and  then  calcined  at  about  300°  C.  in  a  retort,  while  water  spray  and 
a  current  of  air  are  introduced.  This  produces  a  mixture  of  MnC>2, 
MnO,  Mn2O3,  etc.,  containing 
about  70  per  cent  of  the  diox- 
ide. The  process  requires  an 
expensive  plant  and  consumes 
much  fuel. 

The  Weldon  process  *  for 
manganese  recovery  is  the 
most  successful,  and  is  in  use 
in  many  large  works,  since  it 
furnishes  a  continuous  pro- 
cess for  chlorine  making  and 
manganese  recovery.  The 
"still  liquors"  are  neutral- 
ized with  just  sufficient  pow- 
dered limestone  or  chalk  to 
remove  free  acid  and  precipi- 
tate the  iron.  This  is  done 
in  the  tank  (A)  (Fig.  54),  f 
provided  with  a  stirrer.  The 
mixture  is  then  pumped  into  settling  tanks  (B,  B),  where  the  precipi- 
tate deposits.  The  clear  solution  of  manganous  and  calcium  chlorides 
is  then  drawn  into  the  "  oxidizers  "  (C),  where  steam  is  blown  in  to 
heat  it  to  55°  C.  Milk  of  lime  made  from  pure  lime,  especially  free 
from  magnesia,  is  added  from  (E)  until  tests  show  that  the  manganese 
is  all  precipitated;  meanwhile  air  is  slowly  forced  into  (C).  The 
quantity  of  "  milk  "  used  is  noted,  and  then  from  one-half  to  one- 


FIG.  54. 


*  J.  Soc.  Chem.  Ind.,  1885,  525. 


t  After  Lunge. 


118  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

quarter  more  is  added,  and  the  air  blast  turned  on  at  full  strength. 
This  addition  of  an  excess  of  lime  is  necessary  to  hasten  and  com- 
plete the  conversion  of  manganous  hydroxide  into  the  peroxide,  and 
to  prevent  the  formation  of  Mn3O4  ("  red  batch  ").  The  total  quan- 
tity of  lime  used  should  be  such  that  the  precipitate  formed  during 
the  blowing  contains  approximately  two  molecules  of  manganese  per- 
oxide to  one  of  calcium  oxide.  This  is  the  so-called  "  acid  calcium 
manganite  "  (CaO  •  MnCy  -f-  (MnO  •  MnC^),  a  mixture  of  mangan- 
ites  of  calcium  and  manganese.  It  forms  a  thin,  slimy,  black  mass, 
and  is  called  "Weldon  mud."  By  adding  a  little  more  neutralized 
"  still  liquors  "  during  the  "  blowing,"  some  of  the  calcium  oxide  in 
the  calcium  manganite  can  be  replaced  by  manganese  from  the  man- 
ganous chloride  of  these  liquors. 

The  calcium  chloride  liquor,  in  which  the  mud  is  suspended,  is 
run  into  settling  tanks  (D,  D),  from  which  the  supernatant  solution 
is  drawn  off  as  waste.  The  Weldon  mud  is  then  run  into  the  chlorine 
stills  (F,  F)  as  a  thin  paste ;  if  of  good  quality,  it  contains  about  80 
per  cent  of  its  manganese  as  MnC>2,  and  owing  to  its  fine  state  of 
division,  is  readily  decomposed  by  dilute  hydrochloric  acid. 

A  small  loss  of  manganese  occurs  in  the  precipitate  from  the  first 
neutralization  with  marble  or  chalk  dust;  this  loss  is  made  up  by 
decomposing  some  pyrolusite  with  hydrochloric  acid  in  a  small  still 
(G),  and  adding  this  liquor  to  that  from  the  stills  (F,  F). 

The  Weldon  process  works  continuously  and  almost  automat- 
ically, the  materials  being  handled  by  pumps  as  liquids  or  slimes.  It 
is  also  very  rapid,  producing  large  amounts  of  chlorine,  with  but 
slight  loss  (2  to  3  per  cent)  of  manganese  oxide.  But  even  at  its 
best,  only  about  one-third  of  the  chlorine  of  the  hydrochloric  acid  is 
obtained  as  gas,  the  remainder  going  to  waste  as  calcium  chloride  in 
the  liquor  from  the  oxidizers. 

Deacon's  process  *  is  the  most  successful  chemical  method  of 
producing  chlorine  without  the  use  of  manganese.  It  depends  on 
the  oxidation  of  hydrochloric  acid  gas  by  the  oxygen  of  the  air.  This 
is  done  in  the  presence  of  certain  metallic  salts,  which  may  act  as 
"  contact  "  substances,  or  as  carriers  of  oxygen  from  the  air  to  the 
acid,  the  apparent  reaction  being :  — 

4  HC1  +  02  =  2  H20  +  2  C12. 

The  most  satisfactory  "  contact  "  or  "  catalytic  "  substance  for  this 
purpose  is  copper  chloride.  When  cupric  chloride  is  heated  to  400° 

*  Chemical  News  22  (1870),  .157. 


CHLORINE    INDUSTRY 


119 


C.,  it  dissociates  into  cuprous  chloride  and  free  chlorine.  Then,  on 
exposing  the  cuprous  chloride  to  oxygen,  cupric  oxide  is  formed  and 
more  chlorine  set  free.  But  the  cupric  oxide,  reacting  with  hydro- 
chloric acid  gas,  forms  water  and  cupric  chloride.  The  following  are 
the  reactions  involved  :  — 

1)  2  CuCl2  =  Cu2Cl2  +  C12. 

2)  Cu2Cl2  +  O2  =  9  CuO  +  C12. 

3)  2  CuO  +  4  HC1  =  2  CuCl2  +  2  H2O. 

Thus  the  catalytic  substance  is  regenerated  and  the  cycle  of  changes 
begins  anew. 

During  the  dissociation  of  cupric  chloride  32  Calories  is  absorbed, 
but  in  the  other  reactions  60.4  Calories  is  evolved.  Hence  there  is 
a  gain  of  28.4  Calories,  and  theoretically  the  process  once  under  way 
no  addition  of  heat  is  needed.  But,  in  fact,  owing  to  losses  by  radia- 
tion, convection,  and  conduction,  some  heat  must  be  supplied,  and 
the  mixture  of  air  and  hydrochloric  acid  gas  is  heated  to  400°  C.  be- 
fore admitting  it  to  the  "  decomposers."  Since  the  reaction  between 
the  hydrochloric  acid  and  the  oxygen  is  reversible,  an  equilib- 
rium is  established,  and  so  all  of  the  chlorine  is  not  recovered. 

The  plant  for  the  process  (Fig.  55)  *  is  quite  extensive.  The 
gases  from  the  salt-cake  pan  (A),f  together  with  air,  are  passed 
through  cooling  pipes  and  drying  tower  (B)  to  condense 
moisture ;  then  they  go  through  the  "  superheater  "  (C), 
where  the  temperature  is  raised  to  400°  C.  The  hot  gases 
then  pass  into  the  "decomposer"  (D),  a  tall  cast-iron 


FIG.  55. 


cylinder,  containing  bits  of  brick  or  other  porous  material  which  have 
been  soaked  in  a  solution  of  cupric  chloride.  Here  the  above  reac- 
tions take  place,  and  the  resulting  mixture  of  chlorine,  hydrochloric 
acid,  nitrogen,  steam,  and  oxygen,  passes  through  a  condensing  appa- 


*  After  Lunge. 

t  Roaster  gas  is  too  dilute  and  impure. 


120  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

ratus  (E,  E)  to  remove  the  hydrochloric  acid,  and  then  through  a 
coke  tower  (F,  F)  sprinkled  with  concentrated  sulphuric  acid  to 
remove  all  the  moisture ;  finally,  the  dry  chlorine  gas  (with  the 
nitrogen  and  oxygen)  goes  to  the  chambers  where  bleaching  powder 
is  made  (p.  132). 

The  catalytic  substance  in  the  decomposer  becomes  inactive  after 
a  time  (it  seldom  lasts  more  than  four  months)  and  must  be  replaced 
by  fresh  material.  To  accomplish  this  without  interrupting  the  pro- 
cess the  decomposers  are  built  in  separate  compartments,  each  holding 
about  six  tons  of  broken  brick;  every  two  weeks  one  compartment 
is  emptied  and  recharged  without  discontinuing  the  flow  of  gas 
through  the  others.  This  loss  of  activity  in  the  catalytic  substance 
is  attributed  *  to  the  presence  of  sulphuric  acid  in  the  gases  from 
the  salt-cake  furnace.  To  overcome  this  difficulty,  Hasenclever 
devised  a  method  f  by  which  an  aqueous  solution  of  impure  hydro- 
chloric acid,  made  in  the  bombonnes  and  coke  towers,  is  run  into  hot, 
concentrated  sulphuric  acid  (1.42°  Tw.)  while  a  blast  of  air  is  forced 
through  the  mixture.  The  sulphuric  acid  absorbs  the  water  and 
generates  pure  HCl  gas,  which  mixes  with  the  air  in  proper  proportion 
for  use  in  the  decomposer  of  Deacon's  process.  By  this  method, 
84  per  cent  of  the  hydrochloric  acid  gas  is  decomposed  according  to 

the  reaction :  — 

4  HCl  +  O2  =  2  H2O  +  2  C12. 

The  diluted  sulphuric  acid  is  concentrated  and  returned  to  the 
process.  The  dilute  hydrochloric  acid  which  passes  through  the 
apparatus  is  recovered  by  washing  the  chlorine  gas,  and  is  mixed 
with  the  strong  acid  from  the  roasters. 

Owing  to  the  admixture  of  nitrogen  with  the  chlorine,  the  latter 
is  weaker  than  that  furnished  by  the  Weldon  process  and  for  making 
bleaching  powder  a  special  form  of  absorption  chamber  must  be  used. 

When  the  hydrochloric  acid  gas  is  taken  directly  from  the  salt- 
cake  pan  or  from  the  muffle  furnace,  there  is  apt  to  be  some  difficulty 
in  working  Deacon's  process,  owing  to  the  variation  in  the  rate  of 
liberation  of  the  gas.  Much  care  in  the  regulation  of  the  air  supply 
is  necessary. 

The  hydrochloric  acid  gas  from  the  Hargreaves  process  (p.  92)  is 
too  dilute  for  direct  use  in  the  Deacon  apparatus. 

Arsenic  in  the  sulphuric  acid  used  in  the  salt-cake  pan,  or  for  dry- 
ing the  chlorine  gas,  causes  a  loss,  —  in  the  first  case  by  rendering  the 

*  Berichte  d.  chem.  Gesellschaft,  IX,  1070. 
t  Lunge,  Sulphuric  Acid  and  Alkali,  II,  417. 


CHLORINE    INDUSTRY  121 

copper  salt  inactive,  and  in  the  second,  by  forming  hydrochloric  acid, 

thus  :  — 

As2O3  +  4  Cl  +  2  H2O  =  As2O5  +  4  HC1. 

Part  of  this  hydrochloric  acid  combines  with  the  As2Os  to  form 
a  solution  which  condenses  in  the  pipes  between  the  drying  tower 
and  the  bleaching  powder  chambers.  But  some  of  the  acid  is  left  in 
the  chlorine  and  attacks  the  bleaching  powder,  causing  it  to  be 
"  weak." 

The  cost  of  a  Deacon  plant  is  rather  more  than  of  a  Weldon  plant 
of  the  same  capacity  ;  and  while  it  is  theoretically  a  superior  process 
and  requires  less  labor,  it  is  not  yet  in  general  use. 

Several  processes  for  the  preparation  of  chlorine  by  the  use  of 
nitric  and  sulphuric  acids  have  been  proposed. 

Schloesing's  process  *  for  chlorine  by  the  use  of  nitric  and  hydrochloric  acids 
and  manganese  oxides  depends  upon  the  following  reactions  :  — 

2  HC1  +  2  HNO3  +  4  MnO2  =  Mn(NO3)2  +  2  H2O  +  C12. 

The  reaction  is  carried  out  by  heating  the  mixture  of  acids  and  manganese 
peroxide  to  125°  C.,  using  an  excess  of  nitric  acid.  By  heating  the  manganous 
nitrate  to  180°  to  190°  C.,  it  is  decomposed,  and  nitric  acid  may  be  regenerated  from 
the  vapors  by  treating  them  with  air  and  steam,  while  manganese  peroxide  is  re- 

Mn(N03)2  =  Mn02  +  N2O4  ; 
H2O  +O=2  HNOa. 


Wischin,  Just,  and  Alsberge  have  each  patented  modifications  of  the  above 
process.  Alsberge  proposes  to  apply  the  method  to  the  recovery  of  chlorine  from 
the  ammonium  chloride  liquors  of  the  ammonia  soda  process,  by  employing  the 
following  equations  :  — 

1)  2  NH4C1  +  MgO  +  MnO2  =  MgCl2  +  MnO2  +  H2O  +  2  NH3. 

2)  MgCl2  +  MnO2  +  4  HNO3  =  'Mg(NO3)2  +  Mn(NO3)2  +  2  H2O  +  Clt. 

By  evaporating  to  dryness  and  calcining  the  residue,  the  nitrates  are  decom- 
posed thus  :  — 

Mg(NOs)*  +  Mn(NO3)2  =  MgO  +  MnO2  +  2  N2O4  +  O. 

The  peroxide  of  nitrogen  is  converted  to  nitric  acid  by  treatment  with  steam 
ana  air  :  "  N204  +  H20  +  O  =  2  HN03. 

Dunlop's  nitric  acid-chlorine  process  depends  t  upon  one  or  the  other  of  the 
following  equations  :  — 

2  NaCl  +  2  NaNO3  +  4  H2SO4  =  4  NaHSO4  +  N2O4  +  Ch  +  2  H2O. 
4  NaCl  +  2  NaNO8  +  6  H*SO4  =  6  NaHSO4  +  NaO»  +  2  Cl«  +  3  H2O. 

*  Zeit.  angew.  Chemie,  1893,  99,  Lunge  and  Pret.  Wagner's  Jahresbericht, 
1862,  235. 

t  Lunge,  Sulphuric  Acid  and  Alkali,  III,  508. 


122  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

The  mixture  of  salt,  sodium  nitrate,  and  sulphuric  acid  is  heated  in  an  iron 
cylinder  which  is  surrounded  by  the  flames  of  the  fire.  The  vapors  leaving  the  re- 
tort are  passed  through  concentrated  sulphuric  acid  which  retains  the  nitrogen 
oxides,  and  the  chlorine  is  then  washed  with  water  to  remove  any  traces  of  hydro- 
chloric acid. 

The  nitrous  vitriol  obtained  may  be  used  in  the  sulphuric  acid  manufacture. 
The  process  was  worked  on  a  large  scale  at  St.  Rollox,  England,  but  has  been 
abandoned. 

Donald's  process  *  consists  in  passing  the  hydrochloric  acid  vapor  from  a  salt- 
cake  furnace  through  sulphuric  acid  to  dry  it,  and  then  through  a  mixture  of  nitric 
and  sulphuric  acids  kept  at  0°  C.,  when  the  following  reactions  take  place:  — 

2  HC1  +  2  HN03  =  2  H2O  +  N2O4  +  C12. 

.     The  gas  mixture  thus  formed  is  led  through  dilute  nitric  acid,  when  the  follow- 
ing  takes  place  :  -  +  ^  =  HNQ>  + 


By  passing  through  concentrated  sulphuric  acid,  the  nitrous  acid  and  nitrogen 
oxides  are  absorbed,  while  the  chlorine  is  sent  to  the  bleaching  powder  chambers. 

Many  attempts  have  been  made  to  recover  the  chlorine  from  the 
waste  liquors  of  the  ammonia  soda  process,  but  no  one  of  them  has 
yet  proved  a  commercial  success.  Several  of  them  are,  however, 
interesting,  and  deserve  a  few  words. 

Solvay  conducted  elaborate  experiments  in  which  he  tried  to 
realize  the  reaction  :  — 

CaCl2  +  SiO-  +  O  =  CaSiO3  +  C12. 

But  calcium  chloride  is  very  stable,  and  its  decomposition  in  this 
way  is  incomplete,  and  requires  enormous  expenditure  of  heat,  be- 
sides that  used  in  evaporating  the  solution  of  calcium  chloride  to 
dryness. 

Magnesium  chloride  is  more  easily  decomposed  than  calcium 
chloride,  and  several  processes  have  been  devised,  based  on  the  use 
of  this  salt.  It  is  proposed  to  use  magnesium  oxide  or  hydroxide 
instead  of  lime  for  decomposing  the  ammonium  chloride  solution  of 
the  ammonia  process;  by  this,  magnesium  chloride  is  formed  and 
the  ammonia  gas  set  free.  Both  Solvay  and  Weldon,  within  a  few 
days  of  each  other,  patented  methods  for  carrying  out  this  idea. 
But  the  reaction  between  ammonium  chloride  and  magnesia  is  not 
complete,  and  the  solution  of  magnesium  chloride  obtained  is  dilute. 
Viewed  as  a  method  for  chlorine,  more  promising  results  were  ob- 
tained by  using  the  concentrated  magnesium  chloride  mother-liquors 
from  the  Stassfurt  industries  (p.  161),  or  from  other  manufacturing 
operations.  The  magnesium  chloride  solution  is  evaporated  to  dry- 

*  Lunge,  Sulphuric  Acid  and  Alkali,  III,  514. 


CHLORINE    INDUSTRY  123 

ness  at  a  very  low  temperature,  and  the  dried  chloride  is  decomppsed 
by  passing  air  or  steam  over  it  while  heated  to  a  red  heat.  The  re- 
actions are  as  follows  :  — 

1)  MgCl2  +  O  =  MgO  +  C12. 

2)  MgCl2  +  H2O  =  MgO  +  2  HC1. 

The  hydrochloric  acid  obtained  is  used  in  the  Weldon  or  Deacon 
process. 

The  Weldon-Pechiney  *  process  was  the  most  successful  of  the 
magnesia  methods,  though  none  of  them  can  be  said  to  be  profitable. 
In  this,  magnesium  chloride  solution  (made  by  dissolving  the  oxide 
in  hydrochloric  acid,  or  obtained  from  waste  liquors)  is  concentrated 
until  it  contains  six  molecules  of  water  for  each  molecule  of  magnesium 
chloride;  then  1£  equivalents  of  magnesium  oxide  are  stirred  into  the 
solution.  The  pasty  mass  heats  and  soon  hardens  to  a  solid  cake  of 
magnesium  oxy chloride,  which  is  broken  into  lumps  about  the  size  of 
a  butternut,  and  screened  to  remove  the  dust.  The  presence  of  dust 
causes  the  mass  to  cake  badly  during  the  subsequent  drying.  The  lumps 
are  dried  at  a  temperature  not  exceeding  300°  C.,  by  passing  a  current 
of  hot  air  over  them  while  spread  in  a  thin  layer  on  gratings.  Too  high 
temperature  causes  a  loss  of  chlorine  as  such.  If  not  thoroughly  dried, 
chlorine  is  lost  as  hydrochloric  acid.  The  dried  oxychloride  is  quickly 
decomposed  in  a  special  form  of  retort,  which  has  been  heated  by  pro- 
ducer gas  to  a  temperature  of  1000°  C.  before  the  charge  is  introduced. 
Air  is  passed  into  the  retort  to  assist  in  the  decomposition,  which  must 
be  rapid,  or  the  yield  of  chlorine  is  reduced.  Magnesium  oxide  is  left  in 
the  retort,  while  a  mixture  of  chlorine,  hydrochloric  acid,  and  nitrogen 
escapes.  The  hydrochloric  acid  is  recovered  by  washing  the  gases  with 
water,  and  is  used  to  dissolve  part  of  the  oxide  from  the  retort.  The 
chlorine,  mixed  with  nitrogen,  is  used  for  bleaching  powder,  or  for  other 
purposes.  The  residue  of  magnesium  oxide  is  returned  to  the  first  stage  of 
the  process. 

The  yield,  including  the  hydrochloric  acid  recovered,  is  about  88  per 
cent  of  the  whole  amount  of  chlorine  in  the  magnesium  chloride.  About 
40  per  cent  is  obtained  as  free  chlorine,  and  48.5  per  cent  is  returned  to 
the  process  as  MgCl2  and  HC1. 

Of  the  several  methods  that  have  been  devised  for  the  direct  produc- 
tion of  chlorine  from  the  ammonium  chloride  formed  in  the  ammonia 
soda  industry,  Mond's  process,!  which  provides  for  the  recovery  of  the 
ammonia,  has  been  most  carefully  developed,  but  its  practical  success 
is  as  yet  problematical.  It  is  based  on  the  dissociation  of  ammonium 
chloride  into  ammonia  and  hydrochloric  acid,  at  a  temperature  of  350°- 
360°  C. ;  the  hydrochloric  aci.d  being  then  combined  with  some  metallic 
oxide,  to  form  a  non-volatile  chloride,  to  be  later  decomposed  with  libera- 

*  .1.  Soc.  Chem.  Ind.,  1887,  775. 

t  Chemische  Industrie,  1892,  466.  J.  Soc.  Chem.  Ind.,  1887,  140,  216,  217,  440  ; 
1888,  626,  845, 


124  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

tion  of  the  chlorine.     Oxide  of  nickel  was  used  at  first,  but  was  later 
abandoned  in  favor  of  magnesium  oxide.     The  reactions  are :  — 

1)  MgO  +  (2  NH3  +  2  HC1)  =  MgCl2  +  H2O  +  2  NH3. 

2)  MgCl2  +  O  =  MgO  +  C12. 

Since  an  excess  of  magnesia  is  present,  it  is  probable  that  considerable 
magnesium  oxy chloride  is  also  formed,  according  to  the  reaction :  — 

2  MgO  +  2  HC1  =  MgO  •  MgCl2  +  H2O. 

Then  this  is  decomposed  by  the  ah*  (reaction  2),  thus :  — 
MgO  •  MgCl2  +  O=2  MgO  +  C12. 

The  liberated  ammonia  passes  from  the  apparatus  to  the  scrubbers 
of  the  ammonia  recovery  process.  The  complete  recovery  of  this  am- 
monia is  the  first  essential  to  the  success  of  this  method. 

The  ammonium  chloride  is  crystallized  from  the  liquors  of  the  Solvay 
carbonating  towers  (p.  108),  by  cooling  them  to  about  0°  C.  The  dry 
crystals  are  then  vaporized  by  introducing  them  into  melted  zinc  chloride, 
contained  in  an  iron  vessel  lined  with  an  antimony  alloy. 

The  magnesium  oxide,  mixed  with  some  potassium  chloride,  china 
clay,  and  lime,  is  made  into  balls  ("  pills  "),  about  one-half  inch  in  diame- 
ter, and  baked.  The  decomposer  is  then  filled  with  the  "  pills  "  and 
heated  to  360°  C.,  when  vapors  of  ammonium  chloride  are  passed  through 
the  apparatus.  The  reaction  between  the  ammonium  chloride  and 
magnesia  raises  the  temperature  in  the  decomposer  above  400°  C.  Next, 
inert  gases,  such  as  those  from  lime  kilns,  heated  to  550°  C.,  are  passed 
into  the  apparatus  to  drive  out  the  ammonia  and  water  vapors ;  these 
also  heat  the  charge  above  500°  C.  Air,  heated  to  800°  C.,  is  then  ad- 
mitted to  break  up  the  magnesium  chloride  (reaction  2)  and  regenerate 
the  oxide;  it  also  sweeps  out  the  chlorine  formed.  After  cooling  to 
360°  C.  ammonium  chloride  vapors  are  again  introduced  and  the  cycle 
of  operations  is  repeated.  To  secure  uninterrupted  working,  there  are 
usually  four  decomposers  in  each  plant. 

ELECTROLYTIC  PROCESSES  FOR  CHLORINE  AND  CAUSTIC 

SODA 

By  passing  a  current  of  electricity  through  a  sodium  chloride 
solution  the  salt  is  decomposed  into  chlorine  at  the  anode  and  sodium 
at  the  cathode.  But  the  latter  at  once  decomposes  a  molecule  of 
water  of  the  solution,  forming  caustic  soda  and  setting  free  hydrogen. 
Hence  the  products  of  electrolysis  are  chlorine,  caustic  soda,  and 
hydrogen,  of  which  the  last  mentioned  is  of  slight  value  at  present. 

While  electrolysis  appears  very  simple  and  direct  at  first  glance, 
there  are,  in  fact,  serious  difficulties  encountered  in  all  electrolytic 
processes  for  decomposing  salt.  The  migration  velocity  of  hydroxyl 
ions  is  so  much  greater  than  that  of  chlorine  ions,  that  the  former 


CHLORINE    INDUSTRY  125 

carry  a  large  part  of  the  current,  which  tends  to  an  accumulation  of 
the  hydroxyl  ions  in  the  anode  compartment,  where  various  reactions 
take  place,  resulting  in  the  liberation  of  some  oxygen,  which  mixes 
with  the  free  chlorine,  or  attacks  the  carbon  anodes,  forming  carbon 
dioxide  in  the  gas.  This  deposition  of  hydroxyl  ions  also  represents 
a  serious  waste  of  energy.  The  chlorine  diffuses  somewhat,  through 
the  electrolyte,  and  coming  in  contact  with  the  caustic  from  the 
cathode,  increases  the  tendency  to  secondary  reactions. 

To  prevent  this  migration  and  diffusion,  various  devices  have  been 
proposed,  and  the  great  number  of  cells  devised  to  overcome  these 
difficulties  may  be  brought  under  four  general  classes :  — 

I.  Those  in  which  the  products  of  the  electrolysis  are  kept  apart 
by  use  of  a  porous  diaphragm  or  partition,  in  the  cell. 

II.  Those  employing  a  moving  mercury  cathode  to  remove  the 
alkali  metal  from  the  immediate  field  of  decomposition. 

III.  Those  depending  upon  the  specific  gravity  of  the  alkali  solu- 
tion produced,  to  keep  it  away  from  the  action  of  the  chlorine. 

IV.  Those  using  fused  salt  as  electrolyte,  thus  avoiding  secondary 
reactions  by  eliminating  the  hydroxyl  ion  from  the  bath. 

Porous  diaphragms  between  the  anode  and  cathode  seem  simple, 
but  no  material  is  available  which  offers  no  resistance  to  the  passage 
of  electricity,  yet  prevents  the  migration  and  diffusion.  Furthermore 
very  few  substances  can  be  used  for  the  diaphragms,  because  of  the 
destructive  action  of  the  chlorine.  Then,  magnesia,  silica,  etc.,  from 
impurities  in  the  salt,  deposit  in  the  pores  of  the  diaphragm,  and  with 
continued  working  of  the  cell  cause  a  considerable  increase  of  the 
resistance.  The  nascent  chlorine  is  also  very  destructive  to  the 
anode,  and  only  platinum,  or  fused  magnetite  (FesO^  or  iron  oxide, 
which  are  expensive  and  fragile,  or  Acheson  graphite  have  proved 
efficient  in  withstanding  its  action. 

If  the  hydrogen  liberated  at  the  cathode  is  permitted  to  escape 
through  the  solution,  it  stirs  the  liquid,  aiding  the  diffusion  of  the 
chlorine,  and  the  consequent  formation  of  chlorates  and  hypochlorites, 

1)  NaCl  =  Na+Cl. 

2)  Na  +  H2O  =  NaOH  +  H. 

3)  2  NaOH  +  2  Cl  =  NaCIO  +  NaCl  +  H2O. 

4)  3  NaCIO  =  NaClO3  +  2  NaCl. 

5)  NaCIO  +  2  H  =  NaCl  -1-  H2O. 

Reactions  (3),  (4),  and  (5)  cause  loss,  since  they  regenerate  salt. 


126 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


Le  Sueur's  process,*  one  of  the  earliest  of  the  diaphragm  methods, 
has  undergone  several  modifications.  The  diaphragm  is  asbestos 
cloth  which  rests  against  the  iron  gauze  cathode.  The  anodes,  60 
in  each  cell,  are  platinum  wire  gauze.  Diffusion  of  the  sodium  hy- 
droxide through  the  diaphragm  is  hindered  by  feeding  salt  solution 
slowly  into  the  anode  chamber,  thus  keeping  the  level  of  liquid  in 
that  space  slightly  higher  than  in  the  cathode  compartment.  Each 
cell  takes  1000  amperes,  at  6|  volts,  and  the  chlorine  efficiency  is 
claimed  to  be  88  per  cent  or  higher ;  but  the  caustic  production  is 
less  efficient. 

In  Carmichaers  apparatus  f  the  asbestos  diaphragm,  impregnated 
with  Portland  cement,  rests  on  the  horizontal  or  slanted  cathode  at 
the  bottom  of  the  cell ;  above  it  is  a  bell  to  collect  the  hydrogen  given 
off.  The  anode,  suspended  in  the  top  of  the  cell,  is  a  grating  of 
copper  rods,  covered  with  hard  rubber,  through  which  numerous  plati- 
num points  project  into  the  brine.  The  brine  is  fed  in  at  the  top  of 
the  cell  in  a  rapid  stream  of  drops,  so  regulated  that  the  caustic 
formed  at  the  cathode  is  drawn  off  before  it  has  time  to  diffuse  through 
the  liquid.  The  cathode  liquor  produced  contains  about  20  per  cent 
caustic  soda,  and  about  75  per  cent  of  the  salt  is  decomposed.  The 
reaction  is  conducted  at  about  80°  C.,  in  the  top  of  the  cell,  near  the 
anode,  while  the  region  around  the  cathode  is  kept  as  cool  as  possible. 
The  Hargreaves-Bird  cell  |  Fig.  (56)  consists 
pf  a  tall,  narrow,  vertical  cell,  having  two  up- 
right diaphragms  (B,  B)  composed  of  Portland 
cement  with  asbestos,  supported  on  the  vertical 
cathodes  of  iron  wire  gauze.  The  cell  is  8  feet 
long  by  6  feet  high  and  about  14  inches  thick, 
and  is  enclosed  in  a  cast-iron  box,  which  also 
supports  the  cathodes.  The  anode  space  (D,  D) 
between  the  diaphragms  is  filled  with  strong 
brine,  and  the  weakened  brine  leaves  the  com- 
partment through  an  overflow  pipe  near  the 
top  of  the  cell.  By  admitting  steam  to  the 
cathode  space  (C,  C),  between  the  outside  case 
and  the  diaphragms,  the  sodium  ions  passing  through  them  are  com- 
bined to  form  caustic  soda,  which  washes  down  to  the  outlet  pipe. 

*J.  Soc.  Chem.  Ind.,  1892,  963;   1894,  453. 

J.  Am.  Chem.  Soc.,  1898,  868.  U.  S.  Pat.  No.  723,398. 
t  Zeitschr.  f .  angew.  Chemie,  1896,.  537. 
J  J.  Soc.  Chem.  Ind.,  1894,  250,  256;    1895,  166,  1011. 

Eng.  Min.  J.,  1898  (65),  611 ;   1902  (73),  471, 


FIG.  56. 


CHLORINE   INDUSTRY 


127 


If  carbon  dioxide  or  furnace  gases  are  admitted  to  the  cathode  space, 
sodium  carbonate  solution  is  formed;  this  improves  the  efficiency, 
since  the  rate  of  migration  of  the  carbonate  ion  is  less  than  that  of 
the  hydroxyl  ion.  The  anodes  (A)  are  graphitized  carbon  blocks, 
connected  by  copper  rods,  and  buried  in  cement  so  that  only  the 
ends  of  the  carbons  are  exposed  to  the  brine.  Eight  anodes  are 
placed  in  each  cell. 

The  Townsend  cell  *  (Fig.  57)  also  has  vertical  diaphragms  (D) 
of  asbestos  cloth,  the  pores  of  which  are  filled  with  a  mixture  of  iron 
oxide,  asbestos  fibre,  and  precipitated  amorphous  iron  hydroxide. 
This  is  supported  on  the  perforated  iron  plate  cath- 
odes (S,  S),  and  forms  a  chamber  filled  with  brine 
surrounding  the  graphitized  carbon  anodes  (G). 
The  cathode  compartment  is  filled  with  kerosene 
oil  (K),  and  the  drops  of  caustic  liquor  percolat- 
ing through  the  diaphragm,  on  meeting  the  oil, 
assume  the  spherical  shape  and  fall  to  the  bottom 
of  the  cathode  space,  under  the  oil ;  the  caustic 
liquor  then  escapes  by  a  trap  (A).  The  brine  (T) 
is  continuously  added  to  the  anode  space.  These 
cells  take  from  2500  to  5000  amperes  at  an  aver- 
age of  4.7  volts.  The  caustic  liquor  averages  150 
grams  sodium  hydroxide  and  200  grams  of  salt, 
per  litre. 

The   Griesheim-Elektron    process  |    (Fig,    58)    employs    porous 
cement  diaphragms  forming  the   walls  of  the  anode  compartment; 

the  anodes  (A)  are 
cast  from  fused  iron 
oxide.  From  six  to 
twelve  of  these  small 
cells  are  placed  in  an 
iron  vat  (K)  consti- 
tuting  the  cathode 
bath,  and  provided 
FlG-  **•  with  a  run-off  pipe 

for  the  caustic  liquor.  Salt  solution  is  introduced  into  the  anode 
chamber  through  a  pipe  (Z). 

*  Electro-chem.  Met.  Ind.,  1907,  209.     J.  Soc.  Chem.  Ind.,  1907,  746. 

7th  Internat.  Cong.  Appd.  Ghem.  1909,  Sec.  X,  p.  36. 
fBer.   1909    (42),    2897. 
Elektrochemie  wassriger  Losungen.     F.  Forster,  Leipzig,  1905. 


FIG.  57. 


128 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


The  Castner  process  *  was  the  first  successful  method  employing 
a  moving  mercury  cathode.  The  cell  (Fig.  59)  is  divided  into  three 
compartments  and  is  given  a  slight  rocking  motion  by  the  cam  (E). 

The  two  outside  compartments 

|  I  ~     contain  the  iron  cathodes,  and 

the  centre  chamber  contains  the 
carbon  anodes.  The  mercury 
lies  about  one-eighth  inch  deep 
on  the  bottom  of  the  cell,  and 
flows  alternately  from  each  anode 
compartment  into  the  cathode 

FIG.  59.  ... 

chamber,  where  it  is  depnved  or 

its  sodium  content  by  the  water  therein,  forming  caustic  liquor. 
Brine  is  fed  into  the  anode  compartment,  and  the  sodium  set  free 
is  taken  up  by  the  mercury,  forming  amalgam,  which  flows  into 
the  cathode  compartment.  Owing  to  a  slight  reaction  between  the 
sodium  and  chlorine  in  the  anode  chamber,  the  amalgam  is  a  little 
deficient  in  sodium  ions  in  the  cathode  chamber,  and  the  current 
tends  to  decompose  water,  thus  oxidizing  the  mercury.  To  avoid 
this,  a  metallic  connection  is  made  outside  the  cell,  between  the 
iron  cathode  and  the  mercury-amalgam  layer  in  the  caustic  chamber ; 
this  accelerates  the  reaction  between  the  water  and  the  amalgam, 
and  yet  is  independent  of  the  current  in  the  chlorine  chamber. 
Kellner  has  improved  on  the 
Castner  process  by  making 
the  decomposing  cell  sta- 
tionary and  circulating  the 
mercury  through  the  anode 
chamber  by  means  of  an 
Archimedian  screw,  or  wheel 
pump.  The  anodes  of  plati- 
num gauze  weigh  about  1 
gram  each,  and  525  are 
placed  in  each  cell.  The 
cells  take  4000  to  10,000 
amperes  at  4.3  volts,  thus 
reducing  the  size  of  plant  as  compared  with  the  original  cells. 

The  Whiting  cell  f  (Fig.  60)  operates  intermittently,  the  mercury 
remaining  stationary  in  the  anode  compartment  until  an  amalgam  of 


FIG.  60. 


*  J.  Soc.  Chem.  Ind.,  1893,  301.     Eng.  Min.  J.,  1894  (58),  270. 
t  Trans.  Am.  Electrochem.  Soc.,  1910  (17),  327. 


CHLORINE   INDUSTRY  129 

desired  concentration  is  produced.  This  is  then  entirely  removed 
and  a  new  portion  of  mercury  introduced.  By  placing  several  com- 
partments in  parallel  and  operating  them  successively,  the  cell  be- 
comes practically  continuous  in  its  action.  The  cement  cell  consists 
of  a  shallow  box  having  a  decomposing  compartment  (A)  and  an 
oxidizing  space  (B).  The  graphitized  carbon  anodes  (K),  submerged 
in  the  brine  in  (A),  are  supported  from  the  cell  cover  just  above  the 
surface  of  the  mercury  on  the  bottom  of  the  chamber.  The  oxidizing 
chamber  has  inclined  channels  (P,  P)  forming  a  zig-zag  path,  leading 
to  the  pump-pit  (Q).  The  current  flows  from  (K)  through  the  brine 
to  the  mercury,  and  out  by  the  iron  cathode  (R).  The  sodium  set 
free  forms  amalgam,  which  after  a  short  interval  of  time  is  drawn  off 
by  the  valve  (E)  into  the  oxidizing  chamber  (B),  where  the  sodium  is 
removed  by  water  during  the  passage  down  the  incline  (P)  to  the 
pump-pit.  The  mercury,  free  from  sodium,  is  elevated  by  a  wheel 
pump  (J)  and  returned  to  (A).  The  cycle  of  operations  occupies  about 
two  minutes  in  each  compartment.  The  cells  are  six  feet  square 
and  take  about  1400  amperes,  with  voltage  approximately  four.  Chlo- 
rine of  98  per  cent  purity,  with  2  per  cent  hydrogen,  and  pure  caustic 
solution  of  any  desired  strength  up  to  40  per  cent  sodium  hydroxide, 
is  claimed. 

In  Belt's  apparatus  *  the  mercury  is  moyed  into  the  electrolysis 
chamber  by  the  pressure  exerted  by  the  hydrogen  evolved  in  the 
caustic  compartment. 

In  Rhodin's  apparatus  f  the  mercury  is  moved  by  the  centrifugal 
action  of  the  rotating  earthenware  bell  which  serves  as  the  cover  of 
the  anode  chamber.  Neither  the  Bell  nor  the  Rhodin  cells  have  been 
commercially  successful. 

The  disadvantages  of  using  mercury  are  the  tendency  of  other 
metals,  especially  magnesium,  derived  from  impurities  in  the  brine, 
to  accumulate  in  the  amalgam  and  reduce  its  fluidity ;  the  high  volt- 
ages (four  or  over)  necessary ;  the  cost  of  the  mercury  itself,  and  of 
the  installation  in  general. 

The  "  gravity  "  or  "  bell  process  "  t  (Fig.  61)  employs  a  cell 
without  diaphragm  or  mercury.  An  earthenware  bell  (B)  is  suspended 
in  a  tank  containing  brine.  The  anode  (A)  is  near  the  top  of  the 

*  Electrochem.  Ind.,  1903  (I),  505. 

t  J.  Soc.  Chem.  Ind.,  1897,  745;    1900,  418;    1902,  449. 
Electrician,  XL,  8.     U.  S.  Pat.  No.  608,300  (1898). 
I  J.  Soc.  Chem.  Ind.,  1898,  1147;    1904,  545. 
Zeitschr.  Elektrochem.,  1901  (7),  581 ;  1904  (10),  317. 
Ber.  1908  (41),  1789;  1909  (42),  2904. 
K 


130 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


liquid  inside  of  the  bell,  and  the  cathode  (K)  is  outside.  New  brine 
is  constantly  fed  in  by  the  pipe  (C,  C)  and  the  caustic  liquor  overflows 
at  (F),  chlorine  passing  out  at  (D).  The  relatively  large  distance 

separating  the  electrodes  raises 
the  resistance  to  four  volts.  The 
cell  is  of  small  size,  however,  and 
an  extensive  plant  is  necessary 


FIG.  61. 


for  a  commercial  enterprise. 


Electrolysis  in  fused  baths  is  represented  by  the  patents  of  Vautin, 
Heulin,  and  Acker.  The  Acker  process  *  (Fig.  62)  employs  a  bath 
of  melted  lead  for  the  cathode,  on  which  the  fused  salt  rests  ;  a  sodium- 
lead  alloy  forms  and  is  decomposed  by  steam  in  a  special  chamber  (C), 
producing  anhydrous  fused  caustic  directly.  The  cell  is  divided  into 
three  compartments ;  in  one.  (A),  the  salt  fused  at  about  850°  C.  is 
decomposed  and  the  melted  lead  on  the  floor  unites  with  the  sodium. 


FIG.  62. 

The  melted  alloy  flows  into  (B)  and  is  ejected  into  (C)  by  a  steam-jet 
from  (F).  The  melted  lead  and  fused  sodium  hydroxide  separately 
gravity  in  (C),  the  lead  flowing  back  to  (A),  and  the  caustic  is  drawn 
off.  Each  cell  takes  8000  amperes  at  6  to  7  volts.  Much  energy 
is  consumed  in  fusing  the  salt,  and  by  losses  through  radiation,  con- 
duction, and  resistance  at  the  connections,  and  the  up-keep  expense 
is  heavy.  The  only  commercial  trial  of  these  cells  was  at  Niagara 
Falls  but  the  plant  was  destroyed  by  fire  in  1907. 

The  destructive  action  of  caustic  and  chlorine  on  the  diaphragms 
and  other  parts  of  the  electrolytic  apparatus,  and  the  large  size  of 
the  plant  needed  for  a  comparatively  small  output,  are  serious  dis- 

*  Trans.  Am.  Electrochem.  Soc.,  I  (1902),  165.-    U.  S.  Pat.  No.  649,565. 


CHLORINE   INDUSTRY  131 

advantages  of  electrolysis ;  then,  except  in  a  few  places  where  water- 
power  is  cheap,  the  electricity  is  generated  with  steam-engine  and 
dynamo,  a  method  of  low  efficiency,  considering  the  fuel  consumption. 

The  electromotive  force  necessary  to  decompose  salt  is  2.3  volts ; 
but  the  resistance  of  the  bath  and  polarization  increase  this  to  3.5  or 
4  volts.  One  ampere  of  current  yields,  theoretically,  0.00292  pound 
of  chlorine  and  0.0033  pound  of  caustic  soda  per  hour.  If  the 
efficiency  is  80  per  cent,  one  ampere  yields  28.56  grams  NaOH  and 
25.2  grams  Cl  in  24  hours;*  or,  to  make  one  kilo  of  NaOH  in  24 
hours,  the  current  must  be  35  amperes.  If  a  theoretical  yield  were 
obtained,  the  chlorine  evolved  would  make  about  100  pounds  of 
bleaching  powder  for  each  40  pounds  of  caustic  produced.  But  the 
latter,  which  is  in  much  greater  demand  than  bleaching  powder,  can 
be  made  cheaply  from  ammonia  soda ;  this  would  seem  to  limit  the 
electrolytic  processes  to  supplying  bleach  and  chlorates,  while  the 
caustic  must  be  considered  as  a  by-product. 

The  caustic  liquors  produced  by  wet  electrolysis  in  diaphragm 
processes  are  contaminated  with  salt  and  are  dilute,  requiring  much 
evaporation.  As  the  concentration  of  caustic  in  the  electrolyte  in- 
creases, there  is  increased  carrying  of  current  by  the  OH  ions,  with 
liberation  of  oxygen  and  formation  of  water.  This  causes  such 
serious  loss  in  strong  solutions  that  the  practical  limit  of  concen- 
tration is  about  12  or  15  per  cent  of  NaOH.  When  mercury  is  used 
as  cathode,  strong,  pure  caustic  is  produced,  with  less  consumption 
of  fuel. 

HYPOCHLORITES 

By  passing  chlorine  into  a  cold  solution  of  sodium  or  potassium 
carbonate,  a  mixture  of  the  chloride  and  hypochlorite  of  the  alkali 
metal  is  formed.  But  if  any  excess  of  chlorine  is  introduced,  the 
hypochlorite  is  decomposed  into  chloride  and  free  hypochlorous 
acid  (HOC1) :  - 

1)  K2C03  +  H20  +  2  Cl  =  KC1  +  KOC1  -f  H2O  +  CO2. 

2)  K2C03  +  H20  +  4  Cl  =  2  KC1  +  CO2  +  2  HOC1. 

This  solution  of  hypochlorous  acid  is  a  powerful  bleaching  and  oxi- 
dizing agent.  It  was  first  made  about  1789,  and  brought  into  trade 
in  France  as  a  "  bleach  liquor  "  under  the  name  of  eau  de  Javelle,  or 
eau  de  Labarraque.  In  1798  or  1799  Charles  Tennant  took  out  a 
patent  in  England  for  a  "  bleach  liquor  "  made  by  passing  chlorine 

*  Zeitschr.  f.  Elektrochem.,  1895,  21. 


132  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

into  "milk  of  lime,"  by  which  a  solution  of  calcium  chloride  and  hypo- 
chlorite  was  formed  :  — 

2  Ca(OH)2  +  4  Cl  =  CaCl2  +  Ca(OCl)2  +  2  H2O. 

This  bleach  liquor  is  cheaper,  stronger,  and  more  convenient  to  use 
than  bleaching  powder  (see  below),  but  since  it  is  unstable,  evolving 
oxygen  even  when  kept  in  a  closed  vessel  in  the  dark,  it  is  usually 
made  only  for  immediate  use. 

The  tanks  in  which  the  milk  of  lime  is  treated  with  chlorine  are 
provided  with  stirring  apparatus ;  the  temperature  must  not  rise 
much  above  30°  C.,  or  chlorates  are  formed.  A  dilute  chlorine  may 
be  used.  The  density  of  the  solution  obtained  is  about  8°  Tw. 

Calcium  carbonate  suspended  in  water  may  also  be  employed  for 
preparing  bleach  liquor :  — 

CaCO3  +  H2O  +  4  Cl  =  CaCl2  +  CO2   !-  2  HOC1. 

These  liquors  are  chiefly  used  for  bleaching  vegetable  fibres  and 
for  disinfectants. 

The  absorption  of  chlorine  in  milk  of  lime  soon  led  to  trials  of 
dry,  slaked  lime  or  calcium  hydroxide  for  the  same  purpose.  A  dry 
bleaching  powder,  fairly  stable  and  constant  in  strength,  resulted; 
but  its  composition  is  not  the  same  as  that  of  the  bleach  liquor  made 
from  milk  of  lime.  It  was  at  first  supposed  that  a  direct  combina- 
tion took  place  between  the  lime  and  chlorine,  and  that  the  powder 
was  simply  calcium  hypochlorite  [Ca(OCl)2],  so  the  name  "  chloride 
of  lime  "  was  given  to  it.  Other  investigations  led  to  the  view  that 
it  contained  a  mixture  of  calcium  chloride  and  hypochlorite.  But 
this  was  disproved  by  Lunge  *  and  his  students,  who  demonstrated 

Cl 

the   correctness  of   Odling'sf   formula   Ca  .     Hence  it  is  an 

O— Cl 

oxy chloride  of  calcium.  When  dissolved  in  water,  this  forms  hypo- 
chlorite and  chloride  of  calcium. 

For  making  bleaching  powder,  a  pure,  fat  lime  is  desirable.  It  is 
slaked  carefully,  so  that  the  resulting  hydroxide  contains  about  24.5 
to  25.5  per  cent  of  water,  i.e.  there  should  be  a  slight  excess  of  water 
over  that  necessary  to  form  calcium  hydroxide. 

*  Chemische  Industrie,  1881,  289.  Dingl.  J.,  237,  63.  Annalen  der  Chemie, 
219,  129.  Berichte  d.  deutsch,  chem.  Gesellschaft,  1887,  1474.  Zeit.  f.  anorg. 
Chemie,  II,  311. 

t  Odling,  Handbuch  der  Chemie,  I,  p.  59. 


CHLORINE   INDUSTRY  133 

The  absorption  chambers  are  brick,  cast-iron,  or  lead,  and  are 
usually  6.5  feet  high,  and  have  about  200  square  feet  of  floor  area 
per  ton  of  bleach  made  per  week.  Brick  chambers  are  tarred  inside 
to  make  them  gas  tight  and  to  protect  them  from  the  chlorine ;  large 
ones  are  usually  made  from  lead,  much  like  the  vitriol  chambers 
(p.  70),  and  may  have  a  floor  area  of  30  by  100  feet.  The  slaked 
lime  is  sifted  through  screens  with  from  20  to  25  meshes  per  linear 
inch,  as  only  the  fine  powder  is  suitable.  This  is  spread  three  or 
four  inches  deep  on  the  floor,  and  is  furrowed  with  a  special  rake  in 
order  to  assist  the  absorption  by  increasing  the  surface.  The  chlo- 
rine is  introduced  at  the  top  of  the  chamber,  and  settling  to  the 
bottom  because  of  its  density,  is  at  first  rapidly  absorbed  by  the  lime. 

After  a  time  the  process  goes  on  more  slowly,  and  finally  the  gas 
enters  under  some  pressure.  Usually  there  are  three  or  more  chambers 
in  a  series,  the  strongest  chlorine  entering  that  containing  the  most 
nearly  finished  bleach,  and  passing  out  through  that  containing  the 
fresh  lime.  The  degree  of  absorption  of  chlorine  is  judged  by  the 
color  of  the  gases  seen  through  the  glass  "  sights  "  in  the  chamber 
walls.  The  powder  is  turned  over  once  or  twice,  and  the  treatment 
("gassing")  continued  until  tests  show  that  it  contains  from  36  to 
37  per  cent  of  "  available  chlorine."  If  under  strength  ("  weak  "), 
after  the  third  "gassing,"  it  should  be  packed  and  sold  for  what  it 
will  bring,  for  further  exposure  will  cause  the  formation  of  chlorate 
and  chloride  with  loss  of  strength. 

During  the  absorption  considerable  heat  is  generated ;  for  strong 
powder  the  temperature  should  not  exceed  40°  to  46°  C.*  The  chlo- 
rine should  be  admitted  in  a  very  slow  stream,  and  should  be  con- 
centrated, dry,  and  free  from  hydrochloric  or  carbonic  acids.  When 
dilute  (as  from  Deacon's  apparatus),  a  large,  special  chamber  pro- 
vided with  numerous  shelves,  on  which  the  slaked  lime  is  spread 
to  secure  a  greater  absorbing  surface,  is  employed ;  or  the  apparatus 
shown  in  Fig.  63  is  used.  The  yield  from  100  pounds  of  good  lime 
is  about  150  pounds. 

Mechanical  apparatus  (Fig.  63)  for  the  absorption  of  the  chlorine 
is  much  used.  Several  horizontal  cast-iron  cylinders  (A),  set  one 
above  the  other,  each  contains  a  rotating  shaft  carrying  blades  which 
act  as  conveyers ;  the  shafts  in  the  several  cylinders  are  all  driven  at 
the  same  speed  by  a  system  of  gears  (B).  Slaked  lime  is  fed  con- 
tinuously in  a  small  stream  to  the  upper  cylinder  through  (H),  and 
is  carried  by  the  blades  to  the  opposite  end  of  the  cylinder,  where 

*  Lunge  and  Schappi,  Dingl.  J.,  237,  63. 


134 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


it  drops  through  the  opening  (D)  into  the  next,  and  so  on  to  the 
bottom.     Chlorine  enters  the  lowest  cylinder  at  (C),  passes  over  the 

surface  of  the  lime,  ascends 
through  (D)  to  the  next 
higher  cylinder,  and  thence 
up  through  each  in  succes- 
sion, the  unabsorbed  gas 
finally  escaping  at  the  top 
through  (E).  The  bleach- 
ing powder  thus  formed 
collects  in  (F),  from  which 
it  is  dropped  directly  into 
the  casks  for  packing. 


Bleaching  powder  is  a 
yellowish  white  substance, 
which  should  be  perfectly 

dry  and  free  from  lumps.  On  exposure  to  the  air,  it  absorbs  mois- 
ture and  carbon  dioxide,  giving  off  hypochlorous  acid,  the  evolution 
of  which  gives  bleach  its  peculiar  odor.  Good  samples  contain  about 
36  per  cent  "  available  chlorine."  Its  chief  use  is  for  bleaching  vege- 
table fibres  for  the  textile  and  paper  industries. 

In  order  to  liberate  the  chlorine  for  bleaching  purposes,  the  powder 
is  usually  decomposed  by  a  mineral  acid,  thus :  the  fibre,  having  been 
saturated  with  the  bleaching  powder  solution,  is  passed  into  a  dilute 
acid  bath,  where  the  hypochlorite  is  decomposed  and  the  chlorine  set 
free.  The  nascent  chlorine  combines  with  the  hydrogen  of  the  water, 
liberating  nascent  oxygen,  which,  in  turn,  destroys  the  organic  coloring 
matter  in  the  fibre. 

Bleaching  powder,  obtained  from  a  cheaper  base  and  giving  higher 
chlorine  efficiency,  has  replaced  hypochlorites  made  from  alkali  car- 
bonates and  chlorine  (p.  131).  Free  hypochlorous  acid  oxidizes 
hypochlorites  to  chlorates  (NaCIO  +  2  HC1O  =  NaClO3  +  2  HC1),  but 
in  alkaline  solution,  where  no  free  acid  exists,  they  are  relatively 
stable.  The  action  of  chlorine  on  carbonates  liberates  hypochlorous 
acid,  which  thus  destroys  hypochlorite.  The  use  of  alkali  hydroxides 
avoids  this  loss  (2  OH'  +  C12  =  Cl~  +  CIO"  +  H2O).  As  liquid 
chlorine  is  now  a  commercial  article,  hypochlorite  solutions  made  by 
absorbing  the  gas  in  caustic  liquor  are  much  used  ;  this  has  the  advan- 
tage over  lime  that  it  is  easily  washed  from  the  goods  and  forms  no 
insoluble  soaps. 


CHLORINE   INDUSTRY  135 

Hypochlorites  in  dilute  solution  are  strong  oxidizing  agents  on 
organic  matter;  chlorates  do  not  have  this  action,  hence  only  the 
hypochlorite  of  the  solution  is  "  available  "  for  bleaching  purposes, 
and  it  is  only  the  oxygen  of  the  hypochlorite  which  is  active.  The 
chlorine  equivalent  of  this  hypochlorite  oxygen  is  called  the  "  avail- 
able chlorine." 

CHLORATES 

The  chlorates  are  stable  salts  and  are  always  made  by  decomposi- 
tion of  hypochlorites  in  hot  solution  (see  above).  Formerly  chemical 
chlorine  was  run  into  calcium  or  magnesium  hydroxide  (Liebig's 
process).  From  the  reactions  it  is  seen  that  five  times  as  much  chloride 
is  formed  as  chlorate.  The  chlorate  solution  was  double  decomposed 
with  potassium  salts,  with  precipitation  of  potassium  chlorate,  it 
being  less  soluble  in  the  calcium  or  magnesium  chloride  solution.  A 
large  part  of  the  product  was  lost,  however,  in  the  mother-liquors. 

These  methods  are  now  entirely  superseded  by  the  production 
of  the  chlorine  and  alkali  by  electrolysis  of  alkali  chloride  solutions, 
no  diaphragm  being  used,  thus  allowing  anode  and  cathode  products  to 
interact.  The  chloride  regenerated  by  the  above  reactions  is  re- 
electrolyzed,  thus  enabling  the  conversion  of  all  the  chloride  to  chlo- 
rate. Since  the  hypochlorite  is  subject  to  reduction  by  the  nascent 
hydrogen  at  the  cathode  forming  water  according  to  the  reaction, 

2  H  +  CIO"  =  Cr  +  H2O, 

and  to  deposition  at  the  anode  with  loss  of  oxygen,  all  representing 
lost  efficiency,  the  conversion  to  chlorate  is  made  as  rapid  as  pos- 
sible by  keeping  the  solution  hot  and  slightly  acid.  The  current 
efficiency  can  be  made  from  85  to  90  per  cent.  The  voltage 
required  for  the  deposition  of  chlorate  ion  is  much  higher  than 
that  for  chlorine  or  hydroxyl  ion,  hence,  so  long  as  chloride  re- 
mains in  the  bath,  no  chlorate  deposits,  but  when  all  chloride  is  oxi- 
dized, chlorate  deposits,  best  at  high-current  densities,  with  formation 
of  perchlorate,  C1O3~  +  O  =  ClOr,  the  oxygen  coming  from  anodic 
deposition  of  chlorate.  Perchlorates,  especially  those  of  potassium 
and  ammonium,  are  now  made  in  this  way,  and  are  largely  used  for 
explosives  which  possess  great  stability  against  shock. 

The  crude  chlorate  is  purified  by  recrystallizing  from  water,  and 
the  crystals  are  drained  and  washed  in  a  centrifugal  machine,  and 
may  be  sold  as  coarse  crystals ;  or  they  are  ground  to  fine  powder  in 
buhrstone  mills,  care  being  taken  that  no  organic  matter,  dirt,  or 


136  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

metal  (iron,  etc.)  gets  into  the  mill,  lest  an  explosion  result.  No 
fire  should  be  permitted  in  the  building,  and  heating  should  be  by 
steam,  and  lighting  by  electricity.  The  grinding  mill  should  be 
at  a  distance  from  the  main  works. 

Sodium  chlorate  is  much  more  soluble  and  is  more  difficult  to  crys- 
tallize than  potassium  chlorate,  but  it  is,  however,  made  in  large 
quantity. 

Persulphates  of  potassium  and  ammonium  are  made  by  electro- 
lyzing  at  very  low  temperatures  strong  solutions  of  the  acid  sul- 
phates or  acid  carbonates  with  high  current  densities  on  smooth 
platinum  anodes.  The  anions  KSO~4  and  KCO~3  combine  to  form 
persulphate  (K^Os)  or  percarbonate  (K2C2O6),  which  crystallize  as 
moderately  stable  salts.  In  solution  they  are  active  oxidizing  agents, 
and  are  used  to  a  limited  extent  for  bleaching  and  oxidizing  purposes. 

REFERENCES 

Die   Fabrication  von   chlorsaurem   Kali   und   anderen   Chloraten.     Dr. 

Conrad  W.  Jurisch,  Berlin,  1888.     (R.  Gaertner.) 
Die  Darstellung  von  Chlor  u.  Salzsaure,  unabhangig  von  der  LeBlanc 

Soda  Industrie.     Dr.  N.  Caro,  Berlin,  1893.     (R.  Oppenheimer. ) 
Sulphuric  Acid  and  Alkali.     G.  Lunge,  3d  ed.,  Vol.  Ill,  New  York,  1911. 

(Van  Nostrand  Co.) 
J.  Soc.  Chem.  Ind. :  —  1883,  103,  Ferdinand  Hurter. 

1885,  525,  W.  Weldon.  1887,  248,  C.  Longuet  Higgins. 

1887,  775,  James  Dewar.  1896,  713,  Ludwig  Mond. 

Electro-Chemistry.      M.   Leblanc,   translated  by   W.   R.   Whitney  and 

J.  W.  Brown,  New  York,  1907.     (Macmillan  &  Co.) 
Elements  of  Electro-Chemistry.     Lupke. 
Die    Fabrikation    der    Bleichmaterialien.     V.    Holbliug,    Berlin,    1902. 

(Springer.) 
Grundriss  der  reinen  und  angewandten  Elektrochemie.     P.  Ferchlaud, 

Halle  a.  S.,  1903.     (W.  Knapp.) 

Elektrochemie  wassriger  Losungen.     F.  Forster,  Leipzig,  1905. 
Applied  Electrochemistry.    By  M.  deKay  Thompson,  New  York,  1911. 

(Macmillian  Co.) 


NITRIC   ACID 

The  manufacture  of  nitric  acid  is  often  carried  on  in  conjunction 
with  sulphuric  acid  making,  especially  in  those  plants  where  the  liquid 
acid  is  used  in  the  lead  chamber  process.  Large  quantities,  however, 
are  produced  for  general  manufacturing  purposes. 

Practically  all  nitric  acid  is  made  by  treating  sodium  nitrate 
(p.  145)  with  sulphuric  acid  in  cast-iron  retorts.  The  reactions  are 
as  follows :  — 

1)  NaNO3  +  H2SO4  =  NaHSO4  +  HNO3. 

2)  2  NaNO3  +  H2SO4  =  Na2SO4  +  2  HNO3. 

But  it  is  now  thought  that  a  sodium  acid  sulphate*  is  formed  and 
reacts  with  some  of  the  sodium  nitrate, 

3)  NaNO3  +  2  H2SO4  =  NaH3(SO4)2  +  HNO3. 

4)  NaH3(SO4)2  +  NaN03  =  2  NaHSO4  +  HNO3. 

In  practice  the  quantities  of  material  used  do  not  correspond  with 
either  of  these  equations,  but  the  charge  is  so  regulated  that  a  mixture 
of  acid  and  neutral  sulphates  of  sodium,  which  remains  liquid  at  the 
temperature  employed,  is  left  in  the  retort.  If  reaction  (1)  were 
followed,  too  much  sulphuric  acid  would  be  used  for  profitable  work- 
ing, except  in  soda  works,  where  the  resulting  acid  sulphate  is  used 
in  the  salt-cake  furnace.  If  reaction  (2)  is  carried  out,  the  tempera- 
ture must  be  high,  and  the  nitric  acid  is  partly  decomposed  by  the 
heat,  before  it  can  escape  from  the  retort,  causing  smaller  yield  and 
a  product  discolored  by  the  nitrogen  oxides  produced. 

The  sulphuric  acid  employed  is  usually  that  from  the  lead  pan 
evaporation  (sp.  gr.  1.70),  but  for  strong  nitric  acid  the  sulphuric 
acid  should  be  of  92  per  cent  strength,  and  the  temperature  kept  as 
low  as  possible  during  the  distillation.  The  sodium  nitrate  used  is 
purified  Chili  saltpetre  having  96  to  99  per  cent  NaNO3  when  dry. 
Chlorides  should  not  be  present  because  of  the  decomposition  re- 
sulting (p.  141).  The  size  of  charge  ranges  from  500  to  1200  pounds 
or  more  of  nitrate,  and  60°  Be.  sulphuric  acid,  amounting  to  20  or  30 
per  cent  excess  over  the  theoretical  quantity. 

The  apparatus  (Fig.  64)  commonly  used  consists  of  a  horizontal 
cast-iron  cylinder  or  retort  (A)  about  six  feet  long  by  four  or  five  feet 

*  J.  Am.  Chem.  Soc.,  1901  (23),  489. 
137 


138 


OUTLINES   OF   INDUSTRIAL    CHEMISTRY 


diameter,  set  in  a  furnace  in  such  a  way  that  the  flame  plays  over 
its  entire  surface,  heating  all  parts  equally  hot.  Cast-iron  is  but 
little  attacked  by  concentrated  nitric  acid  or  its  vapors,  and  it  is 

important  that  the  retort  be  hot  enough 
in  all  parts  to  prevent  any  condensation 
of  acid.  Retorts  having  exposed  ends 
made  of  sand-stone  slabs,  or  vitrified 
brick  laid  in  cement,  are  sometimes  used. 
The  charge  of  nitre  is  introduced  by  a 
door  in  the  end,  or  side,  of  the  retort, 
and  the  sulphuric  acid  is  run  in  by  a 
pipe  (E).  After  the  reaction  the  fused 
residue  is  run  off  by  (D)  and  on  cooling 
FlG-  64-  forms  the  so-called  "  nitre  cake." 

The  acid  vapors  escaping  from  the  retort  are  condensed  in  earth- 
enware pipes  or  worms,  surrounded  by  water,  or  irf  a  series  of  Woulfe 
bottles  (bombonnes)  (Fig.  44)  with  an  absorbing  tower  at  the  end  to 
catch  the  fumes  escaping  from  the  bottles.  The  dilute  acid  from  the 
tower  may  or  may  not  flow  through  the  series  of  bottles  in  a  direction 
opposite  to  the  movement  of  the  acid  vapors. 

The  most  concentrated  acid  condenses  in  the  first  two  or  three 
bottles  but  is  contaminated  with  sulphuric  acid;  the  last  of  the 
series  contains  dilute  acid,  which  is  contaminated  with  chlorine; 
in  the  middle  bottles  is  pure  acid  of  moderate  strength.  Owing  to 
more  or  less  reduction  of  the  nitric  acid  in  the  retort,  the  condensed 
acid  has  a  yellow  or  red  color,  due  to  absorbed  nitrous  vapors.  For  a 
commercial  acid,  these  must  be  removed  by  "  bleaching  " ;  the  acid 
is  heated  to  about  90°  C.,  and  air  blown  in 
which  carries  away  the  nitrogen  oxides  to  an 
absorbing  tower  for  recovery. 

Guttmann's  apparatus  *  is  much  used.  The 
large  cast-iron  retort  (Fig.  65)  is  made  in  three 
pieces  and  is  entirely  surrounded  by  the  flames 
from  the  grate.  The  retort  gases  pass  into  a 
system  (Fig.  66)  of  vertical  earthenware  pipes 
(A,  A)  having  very  thin  walls  and  joined  at  the 
top  by  bends,  while  they  open  at  the  bottom 
into  a  nearly  horizontal  collecting  pipe  (B,  B) 
which  is  divided  into  sections  by  diaphragms.  The  sections  are  con- 
nected by  U-tubes  passing  under  the  partitions.  The  diaphragms 
*  J.  Soc.  Chem.  Ind.,  1893,  203. 


FIG.  65. 


NITRIC   ACID 


139 


force  the  acid  vapors  to  pass  up  one  pipe  and  down  the  next,  in 
order  to  go  through  the  system.  The  thin  walls  (8  mm.)  of  the 
vertical  pipes  allow  efficient  and  rapid  cooling  by  the  cold  water 
in  the  tank,  and  the  vapors  are  quickly  condensed.  Air  at  80° 
C.  is  injected  from  (F)  into  the  outlet  pipe  (D),  where  it  con- 
verts some  of  the  nitrous  vapors  into  nitric  acid,  increasing  the 
yield.  The  uncondensed  nitrous  vapors  pass  into  the  Lunge-Rohr- 
mann  plate  tower  (E),  where  they  are  absorbed  in  sulphuric  acid  or 


FIG.  66. 

water.  If  the  vapors  remain  in  the  retort  too  long,  part  of  the  acid 
is  decomposed  and  nitrogen  peroxide  is  formed  and  absorbed  by  the 
condensed  acid,  to  which  it  imparts  a  red  color.  Since  there  is  good 
draught  in  this  apparatus,  the  vapors  are  drawn  out  of  the  retort  soon 
after  they  are  evolved,  and  are  at  once  condensed ;  very  little  peroxide 
is  formed,  and  a  light-colored,  concentrated  acid  is  obtained.  It  is 
claimed  that  40°  Be.  acid,  requiring  no  "  bleaching,"  is  made,  and 
with  water-cooled  pipes,  98  per  cent  of  the  theoretical  yield  is 
obtained  as  concentrated  acid,  while  2  per  cent  condenses  in  the 
plate  tower. 

Hart's  tube  condenser  *  (Fig.  67)  for  nitric  acid  is  made  of  glass 
and  earthenware  tubes,  and  is  placed  above  the  brick  arch  over  the 
retort,  thus  occupying  but  little  floor  space.  The  vapor  from  the 
retort  (A)  passes  into  the  pot  (B)  and  thence  through  the  vertical 
earthenware  tube  (C).  From  (C)  to  (D)  extend  a  number  of  glass 
tubes,  inclined  slightly  towards  (C),  and  cooled  by  jets  of  water  from 
the  perforated  pipe  (E,  E).  From  (D)  the  uncondensed  vapors  pass 
*  J.  Soc.  Chem.  Ind.,  1894,  1197.  J.  Am.  Chem.  Soc.,  1895  (17),  576. 


140 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


to  a  plate  tower.  The  acid  condensed  in  the  glass  tubes  flows  back 
into  (C),  and  then  into  (B),  thus  coming  into  contact  with  the  hot 
vapors  from  the  retort.  This  heats  the  acid  so  hot  that  the  nitrous 

vapors  are  driven  out  and 
the  light-colored  acid  is  run 
off  by  the  U-tube  (F).  In 
this  apparatus  the  acid  is 
condensed  very  quickly  and 
little  peroxide  is  formed. 
Frothing  in  the  retort  gives 
no  trouble,  as  any  overflow 
is  caught  in  (B)  and  is  easily 
removed.  The  water  flow 
from  (E)  can  be  so  regulated 
that  nearly  all  of  it  is  evap- 
orated on  the  surface  of  the 
glass  tubes,  giving  great  cool- 
ing effect  with  small  con- 
sumption of  water  ;  any  ex- 
cess of  condenser  water  is 
caught  in  (G).  The  chief 
repairs  are  of  broken  tubes,  which  are  cheaply  and  easily  replaced. 

Valentiner's  process  *  consists  in  distilling  the  mixture  of  sul- 
phuric acid  and  nitre  in  a  vacuum  of  from  60  to  65  cm.  of  mercury,  the 
temperature  being  about  85°  C.,  but  finally  rising  to  160°  C.  There 
is  very  little  decomposition  of  the  nitric  acid,  and  a  large  yield  of  con- 
centrated, light-colored  acid  is  obtained.  The  charge  is  about  1000  kg. 
of  Chili  nitre,  with  the  requisite  amount  of  60°  Be.  sulphuric  acid, 
and  provision  is  made  for  frothing.  The  acid  gases  are  condensed  in 
an  earthenware  worm,  cooled  with  water.  The  uncondensed  vapors 
pass  through  milk  of  lime,  and  then  to  a  bronze  vacuum  pump.  The 
yield  of  acid  is  claimed  to  reach  98  per  cent  of  the  theoretical. 

The  Rhenania  process  f  is  based  upon  the  reactions  between  fused 
sodium  bi  sulphate  and  sulphuric  acid,  forming  the  so-called  poly- 
sulphate,  which  in  turn  reacts  with  the  sodium  nitrate  : 

1)  NaHS04  +  H2SO4  =  NaH3(SO4)2. 

2)  NaH3(SO4)2  +  NaNO3  =  2  NaHSO4  +  HNO3. 


FIG.  67. 


*  J.  Soc.  Chem.  Ind.,  1893,  155  ;   1896,  36  ;   1899,  492,  1122  ;   1901,  544. 

Zeit.  angew.  Chem.,  1899,  269,  1003.     Chem.  Zeit.,  1895,  118  ;   1897,  511. 
t  Chem.  Ind.,  1901,  189,  544,  896,  1189.     J.  Soc.    Chem.  Ind.,   1902,   173. 
J.  Am.  Chem.  Soc.,  1901  (23)  489. 


NITRIC   ACID 


141 


The  apparatus  (Fig.  68)  consists  of  three  iron  retorts;  two  (A) 
heated  to  200°  C.  by  the  waste  heat  from  the  third  (B)  at  300°  C. 
Sodium  nitrate  and  fused  poly- 
sulphate  are  introduced  into  (A), 
where  reaction  (2)  runs  for  a  con- 
siderable time,  and  is  then  com- 
pleted by  drawing  the  charge  into 
the  hotter  retort  (B),  containing 
some  fused  bisulphate  from  the 
previous  operation.  Here  reac- 
tion (2)  is  completed  and  the  last 
of  the  nitric  acid  driven  out. 
Most  of  the  bisulphate  is  then  FlG-  68> 

drawn  from  (B)  and  part  of  it  heated  with  60°  Be.  sulphuric  acid 
in  a  pan  (C)  to  form  polysulphate  for  the  next  charge.  Since 
the  reaction  in  (A)  is  slow,  while  the  final  one  in  (B)  is  rapid,  the 
two  retorts  (A)  are  connected  with  one  retort  (B),  and  by  running 
alternate  charges  in  the  former  to  be  finished  in  (B),  the  process  be- 
comes practically  continuous.  Retort  (A)  yields  concentrated  acid, 
but  that  from  (B)  is  rather  dilute. 

The  strength  of  the  nitric  acid  produced  depends  upon  the  strength 
of  the  sulphuric  acid,  on  the  temperature  of  the  retort,  and  on  the 
purity  of  the  sodium  nitrate.  With  sulphuric  acid  of  1.71  sp.  gr. 
the  nitric  acid  varies  from  1.38  to  1.42  sp.  gr.  (40°  to  42°  Be.).  If 
the  sodium  nitrate  contains  chlorides,  some  of  the  nitric  acid  is  de- 
composed by  the  hydrochloric  acid  produced  :  — 

HN03  +  HC1  =  H20  +  NO2  +  Cl. 

For  chemically  pure  acid,  pure  materials  are  used ;  but  the  common 
acid  may  be  purified  by  treating  with  silver  and  barium  nitrates  and 
redistilling.  Concentrated  acid  cannot  be  distilled  without  some 
decomposition,  and  the  product  must  be  "  bleached  "  by  heating 
and  blowing  in  pure  air. 

Fuming  nitric  acid  is  a  solution  of  nitrogen  peroxide  in  concen- 
trated nitric  acid.  It  is  red  in  color  and  has  a  specific  gravity  of  1.55 
to  1.62.  To  make  this,  perfectly  dry  sodium  nitrate  and  oil  of  vitriol 
(1.84  sp.  gr.)  are  used.  The  reaction  is  carried  so  far  that  neutral 
sodium  sulphate  is  formed  :  — 

2  NaN03  +  2  NaHSO4  =  2  Na2SO4  +  2  NO2  +  H2O  +  O. 

The  nitrogen  peroxide  dissolves  in  the  nitric  acid  to  form  the  fuming 
acid.  A  little  starch  may  be  added  to  assist  in  the  reduction.  An 


142  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

impure  fuming  acid  is  made  by  distilling  a  mixture  of  concentrated 
nitric  and  sulphuric  acids. 

Priestley  and  Cavendish  observed  that  nitric  acid  is  formed  by  the 
action  of  electric  sparks  on  damp  air.  This  results  from  the  direct 
union  of  oxygen  and  nitrogen  at  high  temperature,  to  form  nitric  oxide  : 
N  +  O  ^t  NO.  The  reaction  is  endothermic  and  is  accelerated  by 
high  temperatures,  with  larger  yields  of  nitric  oxide.  But  for  each 
temperature,  an  equilibrium  is  reached,  corresponding  to  a  definite 
percentage  of  nitric  oxide,  and  the  yield  is  not  increased  by  longer 
heating  at  that  temperature.  With  air  at  2000°  C.,  this  equilibrium 
is  reached  almost  instantly,  but  at  1500°  C.  the  reaction  is  slow. 
According  to  Nernst  *  only  0.1  per  cent  by  volume  of  nitric  oxide  is 
produced  at  1500° ;  0.37  per  cent  at  1811°,  and  0.97  per  cent  at  2195°. 
At  higher  temperatures  larger  percentages  are  produced,  until  at  3327° 
about  5  per  cent  of  nitric  oxide  should  be  formed.  But  as  the  reaction 
is  reversible,  there  is  much  decomposition  of  the  product  during  its 
cooling,  so  the  yield  is  decreased.  Below  1500°  C.,  decomposition  of 
the  product  is  slight,  so  very  rapid  cooling  to  this  temperature  is 
essential.  As  the  electric  arc  is  the  most  feasible  method  of  attaining 
high  temperatures,  this  method  of  producing  nitric  acid  direct  from 
the  air  has  attracted  considerable  attention. f 

The  first  technical  attempt  at  the  electrical  fixation  of  atmospheric 
nitrogen  was  the  Bradley  and  Lovejoy  process.  {  A  spark  at  about 
10,000  volts  is  jumped  a  short  distance  through  the  air,  and  the  arc 
formed  is  immediately  broken.  The  machine  makes  about  414,000 
arcs  per  minute,  and  the  nitrogen  oxides  in  the  air  leaving  the  appa- 
ratus are  condensed  in  towers  to  form  nitric  and  nitrous  acids.  The 
process  failed  industrially. 

The  Birkeland  and  Eyde  process  §  has  been  more  successful,  al- 
though mainly  as  applied  to  making  nitrates  rather  than  the  acid. 
It  is  based  on  the  fact  that  in  a  magnetic  field  the  electric  arc  is  de- 
flected to  one  side.  The  furnace  (Fig.  69)  is  a  narrow,  disk-shaped- 
vertical  box  with  fire-brick  lining.  Two  copper  electrodes  (E), 
internally  cooled  by  water,  project  horizontally  into  the  furnace  oppo- 
site to  each  other,  and  one-third  of  an  inch  apart.  Around  the  elec- 

*  Zeitschr.  anorg.  Chem.,  1905  (45),  126;    1906  (49),  213. 

t  J.  Soc.  Chem.  Ind.,  1906,  567  ;  1915,  113. 

j  J.  Soc.  Chem.  Ind.,  1902,  1138.  Electrician,  1902,  684.  U.  S.  Pat.  Nos. 
709,867,  and  709,868. 

§  Zeitschr.  angew.  Chem.,  1905,  217.  Chem.,  Ind.,  1905,  699  ;  1915, 114.  Elec- 
trochem.  Met.  Ind.,  1904,  399 ;  1906,  126. 


NITRIC  ACID 


143 


FIG.  69. 


WATER  OUTFLOW  ,=£ 


trodes  are  the  coils  of  an  electromagnet,  by  which  the  arc  is  deflected 
until  it  breaks  and  a  new  arc  forms,  to  go  through  the  same  cycle. 
The  speed  of  formation,  deflection,  and  breaking 
of  the  arc  is  so  rapid  that  about  700  arcs  per  second 
are  formed,  and  a  "  disk  of  flame  "  is  produced. 
Air  enters  the  oven  by  narrow  channels  (A),  and 
encounters  the  arcs  in  (B),  leaving  the  furnace  by 
the  flues  (C)  mixed  with  about  2  per  cent  of  nitric 
oxide.  The  nitric  oxide  is  oxidized  rapidly  to 
peroxide  and  the  gases  go  to  quartz-packed  ab- 
sorbing towers,  fed  with  water  on  the  counter- 
current  principle.  Nitric  acid  of  50  per  cent 
strength  is  obtained,  which  is  mostly  used  to  make 
calcium  nitrate  for  fertilizer.  Furnaces  of  1000  to  3000  kilowatts 
WATER  .NLET  capacity  are  used,  and  a  yield  of  500  to 

600  kilograms  of  anhydrous  nitric  acid 
per  kilowatt-year  is  claimed. 

The  Schoenherr  process  *  exploited 
by  the  Badische  Anilin  u.  Sodafabrik 
uses  the  apparatus  shown  in  Fig.  70. 
The  arc  is  sprung  inside  of  a  long  narrow 
iron  tube,  having  in  the  lower  end  an 
insulated  iron  electrode  (E),  which  is 
pushed  forward  as  needed  through  a 
copper  water-jacket.  The  air  enters  at 
(A),  passes  through  concentric  pipes  sur- 
rounding the  reaction  tube,  and  enters 
the  latter  near  the  electrode  (E)  by 
means  of  the  tangential  inlets  in  the 
movable  sleeve  (S).  The  air  is  thus 
given  a  spiral,  rotary  motion  through 
the  tube.  The  upper  end  of  the  reaction 
tube  is  water-jacketed  for  one-third  its 
length  and  the  tube  itself  forms  the  other 
electrode.  The  arc  is  started  by  moving 
the  bar  (Z)  to  short-circuit  from  the 
electrode  (E)  to  the  reaction  tube;  the 
arc  thus  starting  in  the  centre  of  the 
FIO.  70.  whirling  current  of  air,  one  end  of  it  is 

*  Zeitschr.  angew.  Chem.,  1338,  1633.     J.  Soc.  Chem.  Ind.,  1915,  115.     Met 
Chem.  Engineering,  1909,  245. 


AIR  ENTRANCE 


144  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

driven  along  the  tube  wall  until  it  reaches  the  water-cooled  section, 
where  it  again  strikes  the  tube  wall.  The  arc  is  thus  extended  to  5  or 
7  metres  length,  and  the  air  surrounding  it  is  in  contact  with  it  for  rel- 
atively long  time.  The  hot  gases  pass  out  of  the  cooled  end  of  the 
reaction  tube  and  enter  an  annular  space  surrounding  the  inlet  pipe, 
to  which  they  impart  some  of  their  heat,  for  pre-heating  the  incom- 
ing air.  Furnaces  taking  1000  H.  P.  are  in  use  and  yields  of  140  grams 
HNO3  per  kilowatt-hour  are  claimed.*  Only  3  per  cent  of  the  total 
energy  supplied  is  used  for  the  production  of  nitric  oxide,  which  is 
oxidized  to  peroxide  by  the  excess  air  present,  when  cooled  below  600° 
C.  The  absorption  of  the  mixed  nitric  oxide  and  peroxide  gases 
from  the  furnace  is  troublesome,  since  the  reaction 

3  N02  +  H20  =  2  HNO3  +  NO 

regenerates  much  nitric  oxide.  If  this,  with  air,  is  led  into  hot  soda- 
liquor,  sodium  nitrite  is  obtained :  — 

2  NO  +  O  =  NO  +  NOa. 

2  NaOH  +  NO  +  N02  =  2  NaNO2  +  H2O,  or 

2  NaOH  +  4  NO  =  N2O  +  2  NaNO2  +  H2O. 

This  method  for  nitrite  has  replaced  the  old  reduction  process  from 
sodium  nitrate  by  metallic  lead.  Milk  of  lime  yields  calcium  nitrite, 
which  is  used  as  a  fertilizer  under  the  name  "  air-saltpetre."  When 
the  dilute  nitric  acid  from  the  water  absorption  is  mixed  with  the 
calcium  nitrite  liquor  and  evaporated  to  dryness,  some  nitrous  acid 
escapes  and  calcium  nitrate  is  obtained,  which  is  sold  as  "  Norway 
saltpetre,"  for  fertilizer. 

The  Pauling  process  f  uses  an  apparatus  shown  in  diagram  by 
Fig.  71.  The  arc  formed  between  the  diverging  electrodes  (A,  A) 
is  elongated  to  about  one  metre,  into  the  fan- 
shaped  space  between  (A,  A)  by  a  blast  of  air 
from  the  nozzle  (E).  Each  furnace  is  said  to  take 
400  kilowatts  at  4000  volts  for  treating  600  cubic 

FIG.  71. 

metres  of  air.  The  gases  after  oxidation  to  per- 
oxide are  absorbed  in  water  to  produce  nitric  acid.,  The  yield  is  said 
to  be  60  grams  of  anhydrous  -acid  per  kilowatt-hour. 

Nitric  acid  is  largely  used  in  making  explosives ;   for  parting  gold 
and  silver ;   in  the  manufacture  of  coal-tar  dyes  and  other  products ; 

*  Zeitschr.  angew.  Chem.,  1909,  1174. 

f  J.  Soc.  Chem.  Ind.  1907,  1204;  1909,  1317;  1915,  115. 

J.  Ind.  Eng.  Chem.,  1914,  68. 


NITRIC   ACID  145 

as  a  "  pickling  liquor  "  for  cleaning  metal ;  for  various  etching 
processes;  and  in  making  metallic  nitrates.  The  pure  acid  is  a 
colorless  liquid,  boiling  at  86°  C.,  but  with  decomposition.  It  also 
decomposes  on  exposure  to  strong  light  and  becomes  yellow  (NOfe). 
Ordinary  commercial  acid  (1.42  sp.  gr.)  distils  at  123°  C.,  contains 
68  to  69  per  cent  HNO3,  and  concentrated  acid  of  1.50  sp.  gr.  con- 
tains about  94  per  cent  HNOs. 


NITRATES 

The  most  important  nitrates  are  those  of  sodium  and  potassium, 
but  ammonium,  lead,  iron,  silver,  strontium,  and  barium  nitrates 
are  used  to  some  extent  in  the  arts. 

Sodium  nitrate,*  also  called  Chili  saltpetre,  is  found  in  natural 
deposits  in  desert  regions  along  the  west  coast  of  South  America, 
especially  near  the  boundary  lines  between  Peru,  Chili,  and  Bolivia, 
in  latitude  20°  to  26°  S.  The  territory  is  now  chiefly  owned  by 
Chili.  The  deposits  extend  about  220  miles  in  length,  and  average 
about  2  miles  in  width. 

The  crude  nitrate,  called  "  caliche,"  varies  from  yellowish  white 
to  brown  or  gray,  and  contains  from  20  to  55  per  cent  NaNO3;  it 
forms  beds  about  5  feet  thick,  lying  near  the  surface,  but  usually 
covered  by  a  conglomerate  of  rock  debris,  cemented  together  by  salt 
and  gypsum.  The  region  is  rainless,  and  water  and  fuel,  being  very 
scarce,  are  used  as  economically  as  possible  in  refining  the  crude 
ore.  The  caliche  is  crushed  and  boiled  with  water  in  tanks  heated 
by  steam  coils,  until  the  liquor  reaches  a  density  of  110°  Tw.,  when 
it  is  run  off  to  crystallize.  The  mother-liquor  retains  most  of  the 
chloride,  iodide,  and  iodate  of  sodium  and  magnesium,  together  with 
about  20  per  cent  of  the  nitrate.  Hence  the  liquors  are  diluted  with 
the  wash  water  from  the  residue,  and  used  again  to  lixiviate  another 
portion  of  caliche.  But  after  two  or  three  repetitions  of  this  process 
the  mother-liquor  is  too  contaminated  for  further  use.  It  is  then 
run  off  and  treated  for  the  recovery  of  the  iodine  (p.  252)  which  it 
contains.  The  residue  from  the  lixiviation  contains  some  nitrate, 
and  is  washed  with  fresh  water,  yielding  a  weak  solution,  which  is 
used  to  dilute  the  mother-liquors  before  using  them  for  leaching. 
The  sodium  nitrate  crystals  are  drained  or  "  centriffed  "  and  dried 
in  the  sun.  They  are  then  packed  and  shipped  as  crude  Chili  salt- 

*  J.  Soc.  Chem.  Ind.,  1890,  664 ;   1893,  128. 


146  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

petre,  containing  from  94  to  98  per  cent  of  NaNOs.  For  many  pur- 
poses this  is  purified  by  recrystallization. 

Deposits  of  sodium  nitrate  have  been  found  recently  in  Upper 
Egypt  and  in  the  trans-Caspian  region,  but  these  have  not  been  much 
developed  as  yet,  and  nearly  all  the  world's  supply  comes  from  Chili. 

The  formation  of  these  beds  is  attributed  to  the  decomposition 
of  sea-plants  under  such  conditions  of  temperature  and  humidity 
that  the  ammonia  produced  was  converted  into  nitrate  by  the  action 
of  the  nitrifying  bacillus,  an  organism  found  in  the  soil.  The  region 
being  rainless,  the  sodium  nitrate  was  not  washed  away. 

Potassium  nitrate,  or  saltpetre,  is  derived  from  three  sources :  — 

1.  Natural  nitrate  beds,  formed  by  the  decomposition  of  organic 
matter  in  warm,  damp  climates. 

2.  Artificial  nitrate  beds,  prepared  especially  for  the  purpose. 

3.  The  decomposition  of  sodium  nitrate  by  potassium  chloride. 
In  many  tropical  countries,  especially  in  India,  Persia,  and  Egypt, 

native  deposits  of  potassium  nitrate  are  found  impregnating  the 
earth  in  the  neighborhood  of  large  cities  and  towns.  This  forma- 
tion is  due  to  the  action  of  the  nitrifying  bacteria,  and  is  not  strictly 
an  oxidation  process.  The  deposits  are  continually  forming,  a 
white  efflorescence  appearing  on  the  surface  of  the  ground.  This 
is  scraped  up,  lixiviated  with  water,  and  the  clarified  solution  evap- 
orated directly,  to  crystallize  the  nitre.  But  all  the  calcium  nitrate 
in  the  mother-liquors  is  thus  lost.  By  adding  potash  obtained  from 
wood  ashes  the  calcium  nitrate  is  decomposed,  and  a  larger  yield  of 
nitre  is  obtained. 

The  artificial  production  of  saltpetre  in  beds  of  decaying  organic 
matter  is  now  of  slight  importance,  though  formerly  largely  prac- 
tised in  Sweden,  Switzerland,  and  France  when  nitre  was  collected 
as  a  part  of  each  farmer's  tax.  By  this  process  putrefying  organic 
matter  is  mixed  with  old  mortar,  or  with  porous  earth  containing 
calcium  carbonate  and  wood  ashes,  and  the  pile  allowed  to  stand  for 
some  months,  being  occasionally  moistened  with  the  liquid  drainage 
from  stables.  The  nitrifying  organisms  soon  impregnate  the  mass 
with  nitrates  of  calcium,  potassium,  and  magnesium.  On  leaching, 
these  go  into  solution ;  when  boiled  with  wood  ashes,  the  calcium 
and  magnesium  are  precipitated  as  carbonates,  while  the  clarified 
liquor  yields  potassium  nitrate  on  concentrating.  The  solution  is 
clarified  by  adding  a  little  glue,  which  combines  with  the  impurities, 
forming  a  scum,  which  is  removed  by  skimming. 

Potassium   nitrate,   made   by   double   decomposition   of   sodium 


NITRIC   ACID  147 

nitrate  with  potassium  chloride,  is  now  the  most  important  from  a 
commercial  standpoint.  The  reaction  is  very  simple  :  — 

NaNO3  +  KC1  =  NaCl  +  KNO3. 

Commercial  potassium  chloride,  containing  about  80  per  cent  KC1,  is 
dissolved  in  water  in  cast-iron,  copper,  or  lead  lined  wood  tanks  hold- 
ing 500  to  600  gallons.  When  the  hot  solution  has  a  density  of 
about  40°  to  42°  Tw.  (1.20  to  -1.21  sp.  gr.),  sodium  nitrate  containing 
95  per  cent  NaNO3  is  added,  and  the  boiling  mixture  well  stirred  for  an 
hour.  On  evaporation,  the  common  salt,  being  less  soluble  than  the 
nitrate,  precipitates,  and  as  much  as  possible  of  it  is  "  fished  "  out, 
the  concentration  being  continued  until  the  density  of  the  solution 
is  100°  Tw.  (1.50  sp.  gr.).  The  liquid  is  allowed  to  stand  a  short 
time  to  settle,  and  then,  while  still  hot,  is  drawn  from  the  sediment 
into  crystallizing  tanks,  where  it  is  actively  stirred  while  cooling. 
This  causes  the  separation  of  the  nitre  as  "  crystal  meal  ",  which  is 
washed  with  a  saturated  solution  of  potassium  nitrate  (or  often  with 
cold  water)  to  remove  the  mother-liquor  and  remaining  sodium 
chloride.  The  wash  waters  and  mother-liquors  are  used  to  dissolve 
the  next  lot  of  potassium  chloride.  One  or  two  recrystallizations 
free  the  potassium  nitrate  from  all  but  a  trace  of  chloride. 

When  the  potassium  chloride  contains  some  magnesium  chloride, 
it  is  best  to  precipitate  the  magnesium  by  soda-ash  before  adding 
the  sodium  nitrate,  since  traces  of  magnesium  chloride  may  other- 
wise remain  in  the  product.  This  salt,  being  deliquescent,  may 
cause  the  nitrate  to  become  wet  on  exposure. 

The  chief  uses  of  potassium  nitrate  are  for  making  gunpowder 
and  explosives,  in  matches,  in  pyrotechnics,  in  assaying,  in  metal- 
lurgical and  analytical  operations,  and  for  curing  meat. 

Ammonium  nitrate  is  now  used  to  a  considerable  extent  •  in  the 
manufacture  of  certain  "  flameless  "  explosives,  and  also,  in  a  less  de- 
gree, for  making  nitrous  oxide  ("  laughing  gas  ").  It  is  usually  made 
by  neutralizing  nitric  acid  with  ammonia.  Attempts  to  produce  it 
by  double  decomposition  of  sodium  nitrate  with  ammonium  salts 
result  in  incomplete  reactions,  and  some  sodium  nitrate  remains  un- 
decomposed.  0 

Lead  nitrate  is  generally  made  by  dissolving  litharge  (PbO)  in 
hot  dilute  nitric  acid.  After  filtering,  the  solution  is  concentrated 
to  a  density  of  100°  Tw.  (1.50  sp.  gr.)  and  allowed  to  crystallize. 

It  is  used  in  dyeing  and  calico  printing,  for  the  manufacture  of 
certain  orange  and  yellow  pigments  (chrome  yellows),  for  some 


148  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

explosives,  and  in  some  kinds  of  matches.  It  is  important  in  that 
it  furnishes  a  moderately  soluble  lead  salt. 

Ferric  nitrate  (nitrate  of  iron)  is  generally  made  by  dissolving 
scrap  iron  in  nitric  acid  of  1.30  sp.  gr.  The  reaction  is  as  follows :  — 

2  Fe  +  8  HN03  =  2  Fe(NO3)3  +  2  NO  +  4  H2O. 

By  concentrating  the  solution,  colorless  crystals,  containing  six  or 
nine  molecules  of  crystal  water,  are  obtained. 

The  aqueous  solution  will  dissolve  ferric  hydroxide,  and  this  basic 
solution  is  much  used  in  textile  coloring.  By  using  an  excess  of 
iron,  and  permitting  the  reaction  to  continue  slowly  after  all  the  acid 
has  been  acted  upon,  a  precipitate  of  insoluble  basic  ferric  nitrate 
ultimately  forms.  The  solution  obtained  in  this  way  is  of  a  red- 
brown  color  and  indefinite  composition.  It  is  chiefly  used  for  blacks 
in  silk  dyeing,  and  for  iron-buff  on  cotton. 

Ferrous  nitrate  is  prepared  by  dissolving  iron  in  cold  dilute  nitric 
acid  (1.10  sp.  gr.).  But  a  considerable  amount  of  ammonium  nitrate 
is  also  formed  in  the  solution,  according  to  the  reaction :  — 

4  Fe  +  10  HNO3  =  4  Fe(NO3)2  +  NH4NO3  +  3  H2O. 

This  solution  is  very  unstable  and  decomposes  when  heated  even 
slightly,  forming  basic  ferric  nitrate  and  liberating  nitric  oxide. 

To  prepare  a  pure  ferrous  nitrate,  decomposition  of  a  ferrous 
sulphate  solution  by  barium  or  lead  nitrate  is  employed :  — 

FeSO4  +  Ba(N03)2  =  BaSO4  +  Fe(NO3)2. 

The  solution  is  filtered  or  decanted  from  the  precipitated  barium 
sulphate. 

There  is  a  preparation  sold  as  "  nitrate  of  iron  "  (probably  so 
called  because  some  nitric  acid  is  used  in  making  it),  which  is  not 
a  nitrate,  but  a  basic  ferric  sulphate  and  sulphate-nitrate  solution. 
A  solution  of  ferrous  sulphate  (copperas)  is  oxidized  by  nitric  acid, 
according  to  the  following  equations  :  — 

1)  6  FeSO4  +  2  HN03  +  2  H2O  =  3  Fe2(SO4)2  •  (OH)2  +  2  NO. 

2)  6  FeS04  +  5  HNO3  =  3  Fe2(SO4)2 '  (NO3)  '  (OH)  +  2  NO  +  H2O. 

3)  6  FeS04  +  8  HNO3  =  3  Fe2(SO4)2  •  (NO3)2  +  2  NO  +  4  H2O. 

4)  12  FeSO4  +  3  H2SO4  +  4  HNO3  =  3  Fe4(SO4)5 "'  (OH)2  +  4  NO 

+  2  H2O. 

Equation  (4)  gives  the  best  product. 

The  solution  of  basic  ferric  sulphate  and  sulphate-nitrates  is  a 
dark  brown-red  liquid,  and  is  much  used  in  silk  dyeing.  It  is  only 


NITRIC   ACID  149 

mentioned  here  because  of  the  frequent  confusion  of  names  in  the 
commercial  article. 

Silver  nitrate  is  made  by  dissolving  the  metal  in  dilute  nitric 

acid  :  ~      6  Ag  +  8  HN03  =  6  AgN03  +  4  H2O  +  2  NO. 

If  the  silver  contains  copper,  the  resulting  solution  of  nitrates  is 
evaporated  to  dryness  and  then  heated  cautiously  to  about  250°  C., 
at  which  temperature  the  copper  nitrate  is  decomposed  into  copper 
oxide,  nitric  oxide,  and  oxygen,  while  the  silver  salt  is  not  altered. 
By  extracting  the  residue  with  water,  the  silver  nitrate  is  dissolved, 
leaving  the  copper  oxide.  The  solution  is  then  evaporated  to  crys- 
tallize the  silver  nitrate. 

The  salt  fuses  unchanged  at  225°  C.,  but  decomposes  if  heated 
nearly  to  redness ;  it  is  cast  in  small  sticks,  and  is  used  in  medicine 
for  a  cautery,  under  the  name  of  lunar  caustic.  Silver  nitrate  has  a 
very  corrosive  action  on  organic  matter.  It  is  largely  used  in  pho- 
tography, and  to  a  lesser  degree  in  pharmacy,  in  the  manufacture  of 
mirrors,  in  preparing  "  indelible  inks,"  and  as  a  chemical  reagent. 

Barium  nitrate  is  made  by  dissolving  the  native  carbonate  (wither- 
ite)  in  hot,  dilute  nitric  acid ;  or  it  may  be  prepared  by  decompos- 
ing a  concentrated  solution  (32°  Be.)  of  barium  chloride,  by  the 
addition  of  sodium  nitrate,  the  less  soluble  barium  nitrate  precipi- 
tating. The  salt  is  purified  by  recrystallization.  It  is  chiefly  used 
for  producing  "  green  fire  "  in  pyrotechnics  and  for  making  barium 
peroxide  (BaO2)  (p.  272).  It  is  also  used  as  an  oxidizing  material  in 
certain  explosives. 

Strontium  nitrate  is  made  by  dissolving  the  native  carbonate 
(strontianite)  in  hot  nitric  acid.  Its  chief  use  is  for  "  red  fire  "  in 
pyrotechnics.  REFERENCES 

Berichte  iiber  die  Entwickelung  der  chemischen  Industrie,  u.  s.  w.     A.  W. 

Hofmann,  1877.     (Vieweg,  Braunschweig.) 

Sulphuric  Acid  and  Alkali.     G.  Lunge.     3d  ed.,  Vol.  I,  1903.     (London.) 
The  Manufacture  of  Explosives.     Oscar  Guttmann.     (Nitric  acid  and 

nitre.) 
Der  Chilisalpeter  und  Zukunft  der  Salpeterindustrie.     H.  Polakowsky. 

Directorium  der   landwirthschaftl.  Hauptgenossenschaft   zu   Berlin. 

Berlin,  1893. 
Die  technische  Ausniitzung  des  atmospharischen  Stickstoffes.     E.  Donath 

u.  K.  Frenzel,  Leipzig,  1907. 

Zeitschrift  f.  angewandte  Chemie.,  1893,  37.  Oscar  Guttmann. 
Journal  American  Chemical  Society,  1896,  576.  Edward  Hart. 
J.  Soc.  Chem.  Ind.,  1893,  128.  J.  Buchanan.  (Sodium  nitrate  in  Chili.) 

1893,  203.     Guttmann.     (Nitric  acid.)     1905,  924. 
Utilization  of  Atmospheric  Nitrogen.     By  Thomas  H.   Norton.     Bull. 

No.  52,  Special  Agents  Series,  Department  of  Commerce  and  Labor. 

Bureau  of  Manufactures.     Washington,  D.C.,  1912. 


AMMONIA 

The  destructive  distillation  of  organic  matter  containing  nitrogen 
yields  more  or  less  ammonia,  and  the  greater  part  of  the  commercial 
supply  is  obtained  from  the  distillation  of  coal  for  coke  or  gas ;  of 
peat ;  of  bituminous  shales ;  of  bones  and  refuse  animal  matter ;  of 
putrid  urine  and  excreta;  of  the  residues  from  the  fermentation  of 
beet  sugar  molasses  for  alcohol;  and  the  waste  gases  from  blast 
furnaces. 

Ammonia  can  be  prepared  synthetically  from  the  nitrogen  of  the 
air  in  several  ways,  but  these  processes  meet  severe  competition  from 
the  ammonia  recovered  as  by-product.  It  was  early  proposed  *  to 
pass  air  over  a  mixture  of  barium  oxide  and  carbon,  at  a  white  heat, 
and  then  to  decompose  the  barium  cyanide  formed,  by  passing  in 
steam  after  the  temperature  had  been  lowered  to  450°  C. :  — 

BaO  +3C+2N+O=  Ba(CN)2  +  CO2. 
Ba(CN)2  +  3  H2O  =  BaO  +  2  CO  +  2  NH3. 

The  process  failed  commercially  because  of  the  great  consumption  of 
fuel. 

The  Frank  and  Caro  process  f  is  based  upon  the  decomposition  of 
calcium  cyanamid  (p.  267)  by  the  action  of  superheated  steam :  — 

CaCN2  +  3  H2O  =  CaCO3  +  2  NH3. 

Yields  of  96  to  97  per  cent  are  claimed,  and  the  ammonia  is  very  pure. 
The  Haber  process  J  depends  on  the  realization  of  the  reaction  :  — 
N2  +  3  H2  =  2  NH3.  Since  this  reaction  takes  place  with  decrease  in 
volume  and  with  a  large  evolution  of  heat  (24  Cal.),  it  is  driven  to 
the  right  by  increase  in  pressure,  but  tends  to  reverse  at  higher  tem- 
peratures. While  the  equilibrium  corresponds  to  high  percentages  of 
ammonia  at  ordinary  temperatures,  dissociation  into  the  elements 
rises  very  rapidly  with  the  temperature.  Moreover,  at  low  tempera- 
tures, the  reaction  rate  is  very  slow.  Haber  has  been  able  to  find 
many  catalyzers,  of  which  he  uses  uranium  powder  and  carbon,  but 
even  with  these  the  rate  is  too  slow  for  commercial  work  below  500°  C. 

*  Compt  rendu,  L,  1100. 

J.  Soc.  Chem.  Ind.,  1882,  364 ;  1883,  328. 

t  Zeitschr.  angew.  Chem.,  1903  (16), 536.  J.  Soc.  Chem.  Ind.,  1903,  809 ;  1908, 
1093.  Met.  Chem.  Eng.,  1915  (13),  213. 

J  Zeitschr.  Elektrochem.,  1910  (16)  244.     J.  Soc.  Chem.  Ind.,  1910,  485,  1453. 

150 


AMMONIA  151 

To  get  reasonable  yields  at  this  temperature,  the  pressure  must  be 
increased  to  150  to  200  atmospheres.  The  reaction  products,  con- 
taining only  a  few  per  cent  of  ammonia,  are  cooled,  the  ammonia 
absorbed  as  a  double  compound  with  suitable  salts,  such  as  ammo- 
nium nitrate,  and  the  gases  returned  to  the  reaction  chamber.  The 
ammonia  is  then  driven  off  by  heat,  and  the  ammonium  nitrate  thus 
regenerated. 

In  Serpek's  process  *  a  mixture  of  calcined  bauxite  and  coke 
is  heated  in  nitrogen,  or  a  producer  gas  containing  65  per  cent  of 
nitrogen,  to  1600°  or  2000°  C.,  in  a  rotary  furnace :  - 

A12O3  +  3  C  +  N2  =  2  A1N  +  3  CO. 

The  aluminum  nitride,  containing  about  30  per  cent  nitrogen,  is  de- 
composed with  water,  according  to  the  reaction 

2  A1N  +  3  H2O=  A12O3  +  2  NH3. 

The  bauxite  enters  the  upper  one  of  two  superimposed  rotary  kilns, 
and  is  heated  by  the  combustion  of  the  carbon  monoxide  issuing  from 
the  lower  kiln ;  the  calcined  alumina  passes  into  the  lower  kiln,  along 
with  the  carbon,  and  here  the  main  reaction  takes  place.  The  alumi- 
num oxide  produced  is  pure  enough  to  meet  market  requirements. 

The  chief  source  of  ammonia  is  the  "  gas  liquor  "  from  the  coke 
and  gas  manufacture  (pp.  36,  314).  The  nitrogen  in  coal  yields  am- 
monia and  cyanogen  compounds  by  destructive  distillation:  in  the 
"  gas  liquor  "  are  found  free  ammonia,  with  ammonium  carbonate, 
sulphide,  and  sulphydrate,  which  are  volatile  with  steam,  and  sul- 
phate, thiosulphate,  sulphite,  sulphocyanide,  and  ferrocyanide,  which 
are  not  volatile.  Gas  liquor  is  valued  according  to  its  percentage  of 
ammonia  as  determined  by  distilling  with  caustic  soda,  absorbing  the 
vapors  in  standard  sulphuric  acid,  and  titrating  the  excess  acid. 

The  gas  liquor  contains  some  tar,  but  on  standing  this  settles,  and 
the  clear  liquor  is  then  distilled  for  the  ammonia.  In  the  simplest 
apparatus,  the  liquor  is  heated  in  one  still  until  the  volatile  salts  are 
expelled,  and  then  is  drawn  into  another  still,  where  "  milk  of  lime  " 
is  added,  and  heated  until  the  fixed  salts  are  decomposed  and  the 
ammonia  driven  off.  The  ammonia  and  volatile  salts  are  absorbed 
in  acid  and  the  hydrogen  sulphide  and  other  foul-smelling  gases  evolved 
are  led  into  the  chimney,  or  decomposed  in  a  Glaus  kiln  (p.  106). 

Generally,  continuous  stills  constructed  on  the  principle  of  the 

*  U.  S.  Pat.  867,615,  888,044,  987,408,  996,032.  Met.  and  Chem.  Ind.,  9 
(1913),  137.  J.  Soc.  Chem.  Ind.,  1913,  1143. 


152 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


Coffey  still,  or  some  special  apparatus,  as  that  of  Feldmann,  or  of 
Griineberg  and  Blum,  are  used  to  distil  the  gas  liquor.  Feldmann's 
apparatus  (Fig.  72)  is  much  used  in  this  country :  the  gas  liquor  from 

the  settling  tank  (F) 
passes  into  the  econo- 
mizer (E),  a  long,  cylin- 
drical shell,  containing 
a  number  of  narrow 
tubes,  through  which 
the  liquor  flows.  In 
the  vessel  (D)  is  sul- 
phuric acid,  to  combine 
with  the  ammonia  va- 
pors passing  from  the 
still  by  the  pipe  (G). 
The  hydrogen  sulphide 
and  carbon  dioxide  lib- 
erated in  (D)  collect 
under  the  bell.  The 
heat  of  the  reaction 
between  the  acid  and 
ammonia  raises  the 
temperature  of  these 
gases  to  a  high  degree, 
and  they  pass  into  the 
jacket  or  shell  surrounding  the  tubes  in  the  economizer,  where  they 
heat  the  liquor  in  the  small  tubes,  so  it  arrives  hot,  at  the  top  of  the 
tower  (AB)  by  the  pipe  (K).  In  the  tower,  the  ammonia  and  its 
volatile  salts  are  driven  out  by  steam  passing  up  through  it.  The 
liquor  containing  the  fixed  ammonia  salts  then  passes  to  the  lower 
part  of  (AB),  where  it  is  mixed  with  "  milk  of  lime,"  while  steam  is 
blown  in.  The  mixture  then  overflows  through  (M)  into  the  smaller 
still  (C)  where  all  the  ammonia  set  free  by  the  lime  is  driven  out  by 
a  steam  jet  from  (S).  This  ammonia  passes  through  (ON)  into  the 
first  tower,  mixes  with  the  gas  escaping  from  (AB),  and  is  absorbed 
in  (D).  The  waste  liquor  escapes  through  (P),  and  the  sludge  of 
calcium  salts  formed  in  (B)  is  drawn  off  at  regular  intervals  through 
(R).  The  still  may  run  for  months  without  stopping. 

The  Griineb erg-Blum  apparatus  is  more  complicated  in  details, 
but  involves  nearly  the  same  principles  as  the  above.  All  of  these 
stills  employ  dephlegmation  (p.  11). 


FIG.  72. 


AMMONIA  153 

Sometimes  in  distilling  gas  liquor,  the  vapors  set  free  by  the  action 
of  the  lime  are  made  to  bubble  through  fresh  liquor  in  a  second  vessel. 
Thus  the  volatile  ammonia  salts  are  expelled  by  the  heat  of  these 
vapors,  and  pass  with  them  to  the  absorption  vats,  while  the  gas 
liquor  is  drawn  into  the  first  vessel  to  be  treated  with  lime.  This 
method  was  used  in  the  old  apparatus  of  Griineberg  and  of  A.  Mallet. 

The  ammonia  gas  set  free  in  any  of  these  stills  is  generally  absorbed 
in  sulphuric  acid.  If  dilute  acid  (80°  to  100°  Tw.)  is  used,  there  is  no 
separation  of  ammonium  sulphate  crystals  in  the  saturator,  and  the 
liquor  is  easily  clarified  from  tar  and  suspended  impurities  before 
evaporating  to  crystallize,  and  yields  a  light-colored  product.  With 
concentrated  acid  (140°  Tw.)  ammonium  sulphate  crystals  separate 
in  the  saturator,  and  are  "  fished  out."  But  they  are  often  discolored. 
As  the  crystals  are  removed,  fresh  acid  is  introduced  into  the  saturator. 
This  is  always  covered  with  a  hood,  from  which  a  pipe  carries  off  the 
foul  gases,  consisting  largely  of  hydrogen  sulphide.  These  gases 
are  often  led  to  a  Glaus  kiln  (p.  106)  to  recover  the  sulphur,  and  avoid 
contaminating  the  atmosphere.  The  ammonia  gas  is  led  into  the 
saturator  through  a  pipe  perforated  with  small  holes  and  submerged 
in  the  acid. 

Plants  for  distilling  peat*  in  Mond  producers  (p.  43)  to  recover 
gas  and  ammonia  are  in  operation  abroad.  The  moist  peat  is  treated 
with  superheated  steam  and  air  at  350°  to  500°  C. ;  the  yield  of  am- 
monia varies  from  40  to  130  kg.  of  ammonium  sulphate  per  ton  of 
peat. 

Ammonia  has  been  made  in  this  country  by  distillation  of  waste 
animal  matter  from  slaughter  houses  and  tanneries.!  The  material  is 
dried  and  put  into  an  upright  iron  cylinder,  provided  with  a  manhole 
at  the  top  and  bottom,  and  having  a  large  perforated  pipe  running  up 
through  the  centre,  about  three-fourths  the  distance  to  the  top.  Chimney 
gases,  forced  by  an  air  compressor  through  a  superheater  (a  furnace 
containing  coils  of  pipe  heated  to  a  bright  red  heat)  into  the  perforated 
pipe,  come  into  direct  contact  with  the  refuse  matter.  The  volatile 
products  pass  out  at  the  top  of  the  retort  into  a  hydraulic  main,  similar 
to  that  in  a  gas  works.  The  tarry  matter  settles  in  the  main  and  the 
gases  pass  through  condensers.  Both  the  condensed  liquors  and  the 
gases  pass  into  absorption  tanks  containing  water ;  the  unabsorbed  gases 
then  go  to  a  "  scrubber  "  (p.  319)  to  remove  the  last  of  the  ammonia, 
and  are  then  burned  under  the  retort.  The  liquor  produced  in  the  ab- 
sorbers and  scrubber  is  distilled  in  an  ammonia  still.  Much  nitrogen 
remains  in  the  coke  in  the  retort. 

*  Zeitschr.  angew.  Chem.,  1906,  1574.    J.  Soc.  Chem.  Ind.  1908,  796  ;  1911,  744. 
t  The  process  failed  in  practice  and  has  been  given  up. 


154  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

A  considerable  amount  of  liquid  ammonia  is  prepared  for  use  in 
ice  machines  (p.  23).  This  is  compressed  into  steel  cylinders,  usually 
containing  about  100  pounds  of  the  liquid. 

Ammonium  sulphate,  as  found  in  commerce,  has  a  light  gray  or 
yellowish  color,  or,  if  carefully  made  and  washed  after  crystallizing, 
is  nearly  white.  When  prepared  by  direct  saturation,  the  color  may 
be  brown  or  nearly  black.  Common  acid  made  from  pyrites  yields 
a  salt  which  is  yellow  in  color,  owing  to  the  iron  or  arsenic  present. 
The  crystals  should  be  washed,  and  dried  in  a  lead-lined  centrifugal 
machine.  When  sold  in  large  quantities  it  is  valued  according 
to  its  content  of  ammonia  or  nitrogen.  Good  samples  contain  from 
23  to  25  per  cent  NH3.  It  is  largely  used  as  a  source  of  nitrogen 
in  making  fertilizers,  but  for  this  purpose  must  be  free  from  sulpho- 
cyanide,  which  is  injurious  to  vegetation.  When  made  by  absorb- 
ing the  gas  in  acid,  little  or  no  sulphocyanide  is  present,  but  by  direct 
neutralization  of  the  gas  liquor  the  cyanide  may  separate  with  the 
sulphate.  The  salt  is  used  as  a  source  of  other  ammonium  com- 
pounds, and  to  a  slight  extent  in  rendering  fabrics,  wood,  and  other 
tissues  non-inflammable.  By  distilling  with  lime  it  yields  a  very 
pure  ammonia  gas,  which  may  be  absorbed  directly  in  water  for  the 
"  aqua  ammonia  "  of  trade ;  or  the  gas  may  be  passed  through  towers 
filled  with  charcoal,  to  remove  any  trace  of  pyridine  or  tar,  before 
absorption.  Any  sulphuretted  hydrogen  may  be  removed  by  passing 
the  gas  over  oxide  of  iron. 

Ammonium  chloride  is  made  by  absorbing  ammonia  gas  in  dilute 
hydrochloric  acid,  or  by  neutralizing  gas  liquor  with  the  acid  directly 
and  evaporating  the  solution.  During  the  evaporation  much  of  the 
tarry  matter  separates,  and  is  skimmed  off.  Some  nuisance  may 
result  from  the  gases  escaping  during  the  neutralizing. 

Another  method  is  to  mix  a  saturated  solution  of  ammonium 
sulphate  with  a  strong  solution  of  salt  or  potassium  chloride.  On 
evaporating  somewhat,  monohydrated  sodium  sulphate  (Na2SO4  •  H2O) 
separates  from  the  hot  liquor,  leaving  the  ammonium  chloride  in 
solution.  On  cooling,  the  ammonium  chloride  crystallizes :  — 

(NH4)2SO4  +  2  NaCl  =  Na2SO4  +  2  NI^Cl. 

The  crystallized  chloride  is  more  or  less  discolored  by  tar,  and 
is  purified  by  sublimation  in  iron  or  earthenware  pots  or  retorts. 
The  ammonium  chloride  collects  on  the  cover  of  the  pot  as  a  thick, 
fibrous  cake,  in  which  form  it  comes  in  trade  under  the  name  of  sal- 
ammoniac.  This  generally  contains  iron  as  an  impurity.  It  was 


AMMONIA  155 

formerly  made  by  subliming  the  soot  obtained  by  burning  dried  camel's 
dung,  but  is  now  nearly  all  made  from  gas  liquor.  The  crystallized 
salt  is  often  sold  under  the  name  of  "  muriate  of  ammonia,"  and  is 
usually  less  pure  than  sal-ammoniac.  Muriate  of  ammonia  is  much 
used  in  the  arts  for  charging  Leclanche  electric  batteries ;  in  the  pro- 
cess of  "  galvanizing  "  iron  ;  in  soldering  liquors ;  for  making  "  rust 
cement  "  for  pipe  joints ;  and  in  textile  coloring. 

Ammonium  carbonate  as  found  in  commerce  is  not  a  pure  salt,  but 
is  a  mixture  of  acid  ammonium  carbonate  (NH4  •  HCO3)  and  a  salt  of 
carbamic  acid  (NH2 -CO2  •  NH4).  The  commercial  salt  is  made  by 
heating  a  mixture  of  the  sulphate  and  powdered  calcium  carbonate  in 
iron  retorts.  The  vapors  are  condensed  in  lead-lined  chambers,  and 
the  impure  product  is  generally  sublimed  in  iron  pots  having  lead  caps. 
A  little  water  is  put  into  each  pot  along  with  the  salt,  this  causing  the 
sublimed  product  to  be  transparent  instead  of  opaque  white.  The 
temperature  of  this  second  sublimation  is  not  much  above  70°  C. 

Ammonium  carbonate  is  transparent  when  fresh  and  pure,  but  on 
exposure  to  the  air  becomes  covered  with  a  white  layer  of  bicarbon- 
ate, owing  to  the  loss  of  ammonia.  It  is  entirely  volatile  when 
heated,  and  from  this  fact  is  derived  its  old  name  of  sal-volatile.  It 
is  used  considerably  in  wool  scouring,  in  certain  baking  powders,  in 
medicine,  and  for  the  preparation  of  "  smelling  salts,"  and  to  some 
extent  as  an  analytical  reagent. 

Ammonium  sylphocyanide  (thiocyanate),  p.  291. 

REFERENCES 

Acetic  Acid,  Vinegar,  Ammonia,  and  Alum.  John  Gardner,  F.I.C., 
F.C.S.,  London,  1885.  (J.  and  A.  Churchill.) 

Chemie  des  Steinkohlentheers.  Dr.  Gustav  Schultz,  2te  Auf.,  Vol.  I, 
Braunschweig,  1886.  (Vieweg  und  Sohn.) 

Das  Ammoniak-Wasser.  Albert  Fehrmann,  Braunschweig,  1887.  (Vieweg.) 

Ammoniak  und  Ammoniak-Praeparate.     Dr.  R.  Arnold,  Berlin,  1889. 

Traitement  des  Eaux  Ammoniacales.  L.  Weill-Goetz  et  F.  Desor,  Stras- 
bourg, 1889.  (G.  Fischbach.) 

Die  technische  Ausniitzung  des  atmospharischen  Stickstoffes.  E.  Donath 
und  K.  Frenzel,  Leipzig,  1907. 

Das  Ammoniak  und  seine  Verbindungen.   J.  Grossmann.    Halle,  a.  S.,  1908. 

Coal  Tar  and  Ammonia.  G.  Lunge,  4th  ed.,  London,  1909.  (Gurney 
and  Jackson.) 

Coal  Gas  Residuals.  Frederick  H.  Wagner.  New  York,  1914. 
(McGraw-Hill  Co.) 


POTASH   INDUSTRY 

Previous  to  the  invention  of  the  Leblanc  Soda  Process,  the  most 
important  alkali  was  potassium  carbonate,  —  potash,  which  was 
nearly  all  derived  from  wood  ashes.  But  with  the  development  of 
the  soda  industry,  the  demand  for  potash  was  greatly  diminished, 
and  at  the  present  time,  soda  has  replaced  it  for  all  except  a  few 
special  purposes. 

The  chief  sources  of  potassium  salts  are :  — 

Wood  ashes. 

Beet-sugar  molasses  and  residues. 

Wool  scourings.     (Suint.) 

Stassfurt  salts. 

Land  plants  take  up  considerable  quantities  of  potassium  com- 
pounds from  the  soil.  When  the  plants  are  burned,  about  10  per 
cent  of  the  weight  of  the  ashes  is  potassium  carbonate,*  which  may 
be  obtained  by  lixiviation.  Potash  from  wood  ashes  is  now  chiefly 
made  in  Russia,  Sweden,  and  America,  the  woods  most  employed 
being  elm,  maple,  and  birch.  Sometimes  the  stumps  and  small 
branches  only  are  burned,  the  trunks  being  used  for  timber.  The 
ashes  are  moistened  slightly,  put  into  tanks  having  false  bottoms  on 
which  straw  is  spread,  and  then  lixiviated  with  warm  water.  The 
lye  so  obtained  is  evaporated  (sometimes  by  the  waste  heat  from  the 
burning  wood)  in  iron  pots  until  it  solidifies  on  cooling.  The  dirty 
brown  mass  is  then  calcined  in  a  reverberatory  furnace  until  all  the 
organic  matter  is  destroyed.  The  product  is  known  as  potash  or 
crude  pearlash.  It  is  white  or  gray  in  color,  and  contains  about 
70  per  cent  K2CO3,  with  some  sulphate  and  chloride  and  sodium  salts. 
By  redissolving  the  crude  potash  in  water,  settling  and  concentrat- 
ing the  solution  until  the  sulphates  and  chlorides  separate  as  crystals, 
a  concentrated  and  pure  lye  is  obtained.  When  this  is  evaporated 
to  dryness  and  the  residue  calcined,  it  yields  a  much  purer  product, 
known  as  "  refined  pearlash,"  and  containing  from  95  to  97  per  cent 
of  IQCOs.  It  is  necessary  that  a  low  heat  be  employed  in  the  cal- 
cination, since  the  charge  fuses  at  a  moderate  temperature. 

Often,  some  quicklime  is  put  in  the  bottom  of  the  tanks  before 
the  ashes  are  introduced.  On  leaching,  the  solution  of  potassium 

*  Those  plants  which  contain  much  silica  or  phosphoric  acid  —  straw  and 
grasses  —  yield  but  little  potash. 


POTASH   INDUSTRY  157 

salts  reacts  with  the  lime,  forming  insoluble  calcium  salts,  and  yield- 
ing more  or  less  potassium  hydroxide  in  the  lye.  The  resulting  prod- 
uct is  then  a  mixture  of  potash  and  caustic  potash. 

In  the  manufacture  of  beet  sugar,  a  very  impure  molasses  re- 
mains, containing  among  other  things  a  large  amount  of  soluble 
potassium  salts.  This  molasses  is  now  generally  fermented,  in 
which  process  the  sugary  substances  are  converted  into  alcohol, 
which  is  distilled  off,  leaving  the  mineral  salts  in  the  liquid  resi- 
due, called  mnasse  or  schlempe.  If  this  is  evaporated  to  dryness  and 
the  mass  calcined,  the  organic  potassium  salts  are  decomposed, 
leaving  in  the  cinder  about  35  per  cent  potassium  carbonate,  and 
a  large  amount  of  chloride  and  sulphate,  together  with  sodium 
salts. 

If  the  mnasse  be  evaporated  to  dryness  and  the  residue  destruct- 
ively distilled  in  retorts,  a  distillate  is  obtained,  containing  organic 
compounds  of  which  methyl  alcohol,  CH3OH,  ammonia,  and  tri- 

/CH3 
methylamine,   N^-CH3,  are  valuable.     The  cinder  in  the  retort  con- 

XCH3 

tains  potassium  salts,  which  are  obtained  in  solution  by  lixiviation, 
and  a  considerable  quantity  of  potash  is  thus  recovered.  Very  often, 
however,  the  ash  is  used  as  a  fertilizer,  thus  returning  the  potash 
to  the  soil. 

Wool  scourings  furnish  some  potash  in  countries  where  much 
wool  is  washed.  Sheep's  wool  as  it  comes  from  the  animal  contains 
from  30  to  75  per  cent  of  its  weight  of  impurities,  consisting  of  dirt, 
sand,  dung,  etc. ;  wool  grease  or  "  yolk,"  a  fat-like  substance,  made 
up  of  cholesterine  and  compounds  of  it  with  oleic,  stearic,  and  palmitic 
acids ;  and  suint,  which  consists  chiefly  of  potassium  salts  of 
oleic,  stearic,  and  other  organic  acids,  with  small  quantities  of  chlo- 
rides and  sulphates  and  nitrogenous  matter.  The  "  suint  "  exudes 
from  the  animal  in  the  perspiration,  and  is  deposited  on  the  wool 
by  evaporation.  It  is  soluble  in  cold  water,  and  is  thus  removed 
in  the  scouring  process.  If  these  wash  waters,  containing  wool 
grease  and  suint,  are  run  into  streams,  pollution  of  the  water  results. 
Prevention  of  this  nuisance,  as  well  as  the  value  of  the  potash,  has 
necessitated  disposal  of  the  washings  in  some  economical  manner, 
and  they  are  usually  evaporated  to  dryness  and  calcined.  If  the 
calcination  is  done  in  closed  retorts,  a  considerable  quantity  of  am- 
monia is  obtained.  The  cinder  is  lixiviated,  and  on  evaporation, 
the  solution  yields,  first,  chlorides  and  sulphates  of  potassium  and 


158  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

sodium,  and  finally  a  pure  potash,  which  averages  nearly  4  per  cent 
of  the  weight  of  the  raw  wool  scoured.  For  the  recovery  and  treat- 
ment of  wool  grease,  see  pp.  369  and  500.  This  utilization  of  wool 
grease  and  suint  is  mainly  practised  in  France,  Belgium,  and  Ger- 
many, where  it  is  done  chiefly  to  prevent  the  pollution  of  the  streams. 
Cheap  fuel  is  essential  to  a  successful  working  of  the  process.  On 
a  small  scale  it  is  not  profitable,  and  the  wash  waters  are  often  run 
on  to  the  fields  as  fertilizer. 

For  potassium  carbonate  from  potassium  chloride,  see  p.  162. 

Certain  seaweeds,  especially  some  varieties  of  brown  algse,  which 
grow  in  rather  deep  water,  have  the  power  of  storing  potassium  salts 
in  large  amount.  For  many  years  the  collection  of  seaweed  in  the 
kelp  industry  (p.  252)  has  been  practised  on  the  coast  of  Scotland  and 
France,  and  from  the  ashes  of  these  plants  potassium  chloride  and 
sulphate,  and  iodine  have  been  recovered.  Recently  the  enormous 
beds  of  these  plants  (locally  known  as  kelp)  along  the  coast  of  Cali- 
fornia and  in  the  Puget  Sound  region  have  attracted  attention  *  as 
possible  source  for  potash  salts  and  iodine.  The  potassium  salts 
may  be  extracted  by  diffusion  processes,  or  by  burning  the  plants  at 
low  temperatures  and  lixiviation  of  the  ash. 

Reports  *  of  large  deposits  of  alunite  (p  286)  in  Utah,  Nevada,  and  Colo- 
rado have  lately  turned  attention  to  the  possibility  of  extracting  potash 
from  this  basic  alumino-potassium  sulphate.  By  roasting,  sulphur  trioxide 
is  evolved,  the  alumina  rendered  insoluble,  and  potassium  sulphate  may  be 
lixiviated  from  the  mass.  The  investigation  of  these  deposits  is  not  yet 
completed. 

By  far  the  most  important  source  of  potassium  compounds  at  the 
present  time  is  the  great  natural  deposit  of  potassium  salts  found 
at  Stassfurt  and  Leopoldshall,  near  Magdeburg,  Germany.  This 
consists  of  immense  beds  of  various  salts,  which  have  been  deposited 
from  sea  water.  They  were  discovered  in  attempting  to  reach  the 
underlying  rock-salt,  but  because  of  the  large  proportion  of  potas- 
sium and  magnesium  chlorides,  the  material  was  at  first  thrown 
aside  as  worthless,  the  name  applied  to  it,  —  "  abraumsalze,"  —  indi- 
cating the  small  value  attached  to  it.  But  in  1861^  methods  were 
devised  by  which  potassium  chloride  and  sulphate  could  be  obtained 
cheaply  from  the  Stassfurt  salts,  and  since  these  furnish  a  valu- 
able source  for  nearly  all  other  potassium  salts,  a  rapid  development 
of  the  industry  followed. 

*  Fertilizer  Resources  of  the  United  States.  Senate  Document  No.  190, 
62d  Congress.  Washington,  1912. 


POTASH   INDUSTRY  159 

Sea  water  contains  about  3.5  per  cent  of  solids,  consisting  of  :  — 

Sodium  chloride     .........  76.49  per  cent  * 

Magnesium  chloride  ........  10.20 

Magnesium  sulphate  ........       6.51 

Calcium  sulphate  .........       3.97 

Potassium  chloride     ........       1.98 

Magnesium  bromide  1  0  85          " 

Calcium  bicarbonate,  etc.  / 

By  the  evaporation  of  sea  water  under  certain  conditions,  these 
salts,  together  with  various  double  salts,  formed  by  mutual  inter- 
reactions,  crystallize  in  the  order  of  their  relative  insolubility. 

The  Stassfurt  deposit  was  undoubtedly  formed  by  the  evaporation 
of  sea  water,  under  peculiar  conditions.  The  mode  of  formation  has 
been  studied  by  many  investigators,  to  whose  memoirs  the  reader  is 
referred  for  full  explanations,  f  The  deposit  is  nearly  3000  feet  thick, 
and  about  16  different  salts  have  been  identified  in  the  various  strata. 
The  more  important  salts  and  their  composition,  are  given  below  :  — 

Gypsum     ......  CaSO4  •  2  H2O 

Anhydrite  ......  CaSO4 

Kamite       ......  K2SO4,  MgSO4,  MgCl2  -  6  H2O 

Carnallite  ......  KC1,  MgCl2  •  6  H2O 

Kieserite    ......  MgSO4-H2O 

Polyhalite  ......  K2SO4,  MgSO4,  2  CaSO  4  -2  ILO 

Rock-Salt  ......  NaCl 

Sylvine       ......  KC1 

Tachydrite      .....  CaCl2,  2  MgCl2  •  12  ILO 

Boracite     ......  2  (Mg3B8O15)  +  MgCl2 

Astrakanite     .....  MgSO4,  Na2SO4  •  4  H2O 

Schoenite   ......  K2SO4,  MgSO4  •  6  H2O 


The  beds  are  not  sharply  defined  layers  of  separate  salts,  the  de- 
posit being  generally  regarded  as  containing  four  principal  "  regions." 

The-rock-s.alt  or  anhydrite  region  is  the  lowest  of  these.  This 
consists  of  thin  layers  of  very  pure  rock-salt,  separated  by  narrow 
strata  (one-fourth  of  an  inch  thick)  of  anhydrite.  The  anhydrite  is 
separated  from  the  salt  mechanically,  and  the  latter  is  then  ground 
for  use  directly.  This  bed  is  nearly  2000  feet  thick  in  places. 

The  polyhalite  region,  about  200  feet  thick,  is  above  the  rock- 
salt  region.  It  is  composed  of  91  per  cent  of  rock-salt,  and  6j  per 
cent  of  polyhalite,  with  smaller  quantities  of  other  salts. 

*  Regnault  (Thorpe's  Dictionary  of  Applied  Chemistry,  Vol.  IV,  340). 
t  A  very  good  account  is  given  in  Thorpe's  Dictionary  of  Applied  Chemistry, 
Vol.  IV,  pp.  340-341.     Also  see  Pfeiffer's  Handbuch  der  Kali-Industrie. 


160  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

The  kieserite  region,  lying  next  above,  is  about  185  feet  thick, 
and  contains  65  per  cent  rock-salt,  17  per  cent  of  kieserite,  13  per 
cent  carnallite,  and  5  per  cent  of  other  salts. 

The  carnallite  region  lies  nearest  the  surface,  and  is  about  140  feet 
thick.  This  is  the  most  important  and  contains ;  — 

Carnallite 55-60  per  cent 

Rock-salt 20-25  per  cent 

Kieserite 16  per  cent 

Tachydritel 4  per  cent 

Boracite      j 

In  parts  of  this  region,  changes  have  taken  place  through  the  ac- 
tion of  water,  by  which  considerable  deposits  of  kainite  and  sylvine 
have  been  formed.  The  composition  of  raw  carnallite  is  about  as 
follows :  —  j  jj 

..  15.7  per  cent 

.     .  21.3 

.     .  21.5 

-,    •  0.3 

.  --v.  13.0        " 

.     .  00.0 

.     .  26.2 

Insoluble 00.0        "          ,     .     .  2.0 

The  crude  carnallite  is  often  colored  a  deep  red  by  the  presence 
of  iron  compounds. 

The  present  commercial  supply  of  potassium  chloride,  and  inci- 
dentally of  other  potassium  compounds,  is  obtained  from  carnallite. 
The  crude  material  is  treated  with  the  hot  mother-liquor  from  a 
previous  lot,  in  an  iron  kettle  having  a  stirring  apparatus  and  a  false 
bottom.  This  mother-liquor  contains  about  20  per  cent  MgCl2,  which 
prevents  the  solution  of  the  rock-salt  and  kieserite,  but  does  not 
hinder  the  dissolving  of  the  carnallite.  The  action  of  the  magnesium 
chloride  solution  is  continued  until  the  hot  liquor  reaches  a  density 
of  1.32  sp.  gr.,  when  it  is  drawn  off  from  the  sludge  and  allowed  to 
cool  slowly.  At  this  density,  the  greater  part  of  the  potassium 
chloride  crystallizes  on  cooling,  leaving  the  magnesium  chloride  and 
some  potassium  chloride  still  in  solution.  This  liquor  is  then  further 
concentrated,  until  it  contains  about  30  per  cent  magnesium  chloride. 
On  cooling,  crystals  having  the  composition  KC1,  MgCl2  •  6  H2O,  — 
artificial  carnallite,  —  separate,  leaving  only  the  excess  of  magnesium 
chloride  in  solution.  The  artificial  carnallite  is  decomposed  with 
water,  and  the  potassium  chloride  crystallized  out,  leaving  the  mag- 


Potassium  chloride 

.     16.2  per  cent 

Magnesium  chloride   . 

.     24.3 

Sodium  chloride     .     . 

.     18.7 

Calcium  chloride    .     . 

.       0.2 

Magnesium  sulphate  . 

.       9.7 

Calcium  sulphate  .     . 

.       2.1 

Water 

28.8 

POTASH   INDUSTRY  161 

nesium  chloride  in  solution  ;  a  part  of  this  liquor,  diluted  with  the  wash 
water  from  the  sludge,  is  used  to  extract  the  next  portion  of  raw  carnal- 
lite.  The  potassium  chloride  is  washed  with  a  small  portion  of  very 
cold  water,  to  remove  the  common  salt. 

The  residue  from  the  solution  of  the  raw  carnallite  consists  largely 
of  kieserite  mud  (MgSO4  •  H2O),  which  is  insoluble  in  water;  but  on 
standing  for  some  time  in  contact  with  water,  it  passes  over  into  the 
soluble  Epsom  salts  (MgSO4  •  7  H2O).  At  an  intermediate  stage  of 
the  hydration,  the  mud  solidifies  in  a  manner  similar  to  plaster  of  Paris 
when  mixed  with  water.  When  this  solidification  is  about  to  take 
place,  the  mud  is  moulded  into  blocks,  which  become  very  hard,  and 
in  which  form  it  is  shipped.  But  after  some  time  they  take  up  moisture 
from  the  air,  and  fall  to  a  powder  of  Epsom  salt. 

Glauber's  salt  is  made  at  Stassfurt  in  the  winter  time  as  follows : 
Solutions  of  common  salt  and  magnesium  sulphate  (e.g.  from  kieserite) 
when  kept  below  0°  C.  will  react  together,  thus  :  — 

MgS04  +  2  NaCl  =  MgCl2  +  Na2SO4, 

and  at  the  low  temperature,  the  sodium  sulphate  crystallizes  to  form 
Na2SO4  •  10  H2O. 

Kainite  (K2SO4,  MgSO4,  MgCl2  •  6  H2O)  is  extensively  used  in  the 
crude  state  as  a  fertilizer.  Some  of  it,  however,  is  treated  for  potas- 
sium sulph'ate,  by  the  method  of  H.  Precht.  When  heated  with 
water  under  pressures  of  four  or  five  atmospheres,  kainite  decomposes 
into  a  double  potassium-magnesium  sulphate,  magnesium  chloride, 
and  potassium  chloride,  thus  :'  — 

3(K2SO4,  MgSO4,  MgCl2  -  6  H2O)  = 

2(K2SO4,  2  MgSO4  -  H2O)  +  2  MgCl2  +  2  KC1  +  16  H2O. 

The  double  potassium-magnesium  sulphate  separates  in  crystals, 
and  is  freed  from  chlorides  by  washing;  during  the  washing,  one 
molecule  of  the  magnesium  sulphate  is  also  removed,  and  a  salt  of 
the  composition,  K2SO4,  MgSO4,  remains.  This  is  dried  and  calcined 
and  sold  as  double  potassium-magnesium  sulphate ;  or  it  may  be  de- 
composed directly  by  treating  with  a  solution  of  potassium  chloride 
of  1.142  sp.  gr. :  - 

K2SO4,  MgSO4  +  2  KC1  =  MgCl2  +  2  K2SO4. 

The  potassium  sulphate  is  separated  from  the  magnesium  chlo- 
ride by  crystallization. 


162  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

Potassium  sulphate,  made  from  kainite  as  above,  or  by  the  action 
of  sulphuric  acid  on  potassium  chloride,  is  largely  used  as  a  fertilizer 
and  for  the  manufacture  of  potassium  carbonate. 

Potassium  chloride,  chiefly  obtained  from  carnallite,  is  extensively 
used  for  preparing  other  potassium  salts,  especially  the  nitrate  (p.  146), 
sulphate,  and  carbonate. 

Potassium  carbonate  or  potash  is  made  from  potassium  chloride 
by  the  Leblanc  process,  in  the  same  way  as  soda-ash  from  salt.  But 
the  ammonia  process  cannot  be  employed,  because  the  acid  carbonate 
of  potassium  (KHCO3)  is  soluble  in  ammoniacal  solutions,  and  does 
not  precipitate. 

Potassium  carbonate  is  sold  in  trade  under  the  name  of  potash 
or  pearlash,  and  is  used  chiefly  in  the  glass  industry,  for  caustic  potash 
and  for  chroma tes  of  potassium.  A  considerable  quantity  is  bought 
by  soap  makers,  and  causticized,  the  solution  being  used  for  soft  soaps 
(p.  373). 

Caustic  Potash  is  made  in  the  same  way  as  caustic  soda  (p.  101). 
The  mother-liquors  from  the  black-ash  lixiviation  are  decomposed 
directly  with  slaked  lime.  Caustic  potash  is  much  more  deliques- 
cent than  caustic  soda,  and  is  generally  made  where  it  is  to  be  used. 

In  soap  making,  it  was  formerly  customary  to  saponify  the  fat 
with  caustic  potash,  and  then  to  add  common  salt.  An  interchange 
between  the  potassium  and  sodium  took  place,  and  a  hard  sodium 
soap  resulted.  But  as  soda  is  now  cheaper,  and  yields  a  hard  soap 
directly,  potash  soaps  are  only  used  for  special  purposes. 

Potassium  nitrate  (see  p.  146). 

Potassium  bichromate  (K2Cr2O7)  is  made  by  roasting  chromite  (a 
native  oxide  of  chromium  and  iron)  with  potash,  lixiviating  the 
fused  mass  with  water,  and  adding  enough  sulphuric  acid  to  convert 
the  neutral  potassium  chromate  into  bichromate.  The  reactions 
involved  are  as  follows  :  — 

Cr2O3  +  3  O  =  2  CrO3. 

CrO3  +  K2CO3  =  K2CrO4  +  CO2. 

2  K2CrO4  +  H2SO4  =  K2SO4  +  K2Cr2O7  +  H2O. 

The  finely  powdered  chrome  ore  is  mixed  with  lime  and  potash, 
and  roasted  at  a  bright  red  heat,  with  free  access  of  air  and  frequent 
stirring.  After  several  hours  the  chromic  oxide  is  all  oxidized  to 
chromium  trioxide  (CrO3),  which  combines  with  the  lime  and  pot- 
ash to  form  neutral  chromates  of  calcium  and  potassium.  The  mass 


POTASH  INDUSTRY  163 

is  then  treated  with  a  hot  solution  of  potassium  sulphate,  which 
forms  potassium  chromate  from  the  calcium  chromate.  The  solu- 
tion of  neutral  potassium  chromate,  when  saturated,  is  drawn  off 
and  settled.  It  is  then  decomposed  in  lead-lined  tanks,  by  the  addi- 
tion of  sulphuric  acid.  Since  potassium  bichromate  is  very  much 
less  soluble  in  cold  solution  than  the  neutral  chromate,  about  three- 
fourths  of  the  total  amount  of  bichromate  formed  precipitates.  The 
remaining  liquor,  containing  potassium  sulphate,  is  used  to  leach 
a  new  portion  of  cinder.  The  precipitated  bichromate  is  recrystal- 
lized  from  water. 

The  addition  of  lime  to  the  furnace  charge  is  necessary  to  prevent 
the  fusion  of  the  mass,  and  to  keep  it  porous,  so  that  the  oxidation  of 
the  chrome  is  more  complete. 

Potassium  bichromate  is  much  used  as  a  source  of  other  chromium 
compounds;  as  an  oxidizing  agent  in  dyeing  and  making  coal-tar 
dyes ;  as  a  mordant ;  as  -a  bleaching  agent  for  oils  and  fats ;  and  for 
the  preparation  of  leather  in  the  chrome  tannage  processes. 

REFERENCES 

Die  Industrie  von  Stassfurt  u.  Leopoldshall.     G.  Krause.     Coethen,  1877. 

Haudbuch  der  Kali  Industrie.     E.  Pfeiffer,  1887. 

Die   Salz   Industrie  von   Stassfurt.     Dr.   Precht,    Stassfurt,    1889.     (R. 

Weicke.) 

Die  Stassfurter  Kali-Industrie.     G.  Lierke,  Wien,  1891.     (Hilschmann.) 
Die  nprddeutsche  Kaliindustrie.     Precht-Ehrhardt,  Stassfurt,  1906. 
Chemie  und  Industrie  der  Kalisalze.     Erdmann,  Berlin,  1907. 
Die  deutsche  Kaliindustrie.     Dr.  K.  Kubierschky,  Halle,  a.  S.,  1907. 
Die  Verwertung  des  Kalis.     Kiersche,  Halle,  a.  S.,  1907. 
Fertilizer  Resources  of  the  United  States.     Senate  Document  No.  190, 

62d  Congress.     Washington,  1912. 
J.  Soc.  Chem.  Ind.,  1883,  146.     C.  N.  Hake. 
Chemische  Zeitung,  1890,  Grief.     1891,  Heyer. 
Dingler's  polytechmsches  Jour.     Vol.  241.     Precht. 


FERTILIZERS 

Growing  plants  abstract  from  the  soil  and  air  certain  elements,  as 
carbon,  hydrogen,  potassium,  calcium,  sulphur,  phosphorus,  and 
nitrogen,  and  apply  them  to  their  nourishment.  To  a  less  degree, 
silicon,  iron,  sodium,  magnesium,  and  chlorine  are  taken  up  also. 
Natural  weathering  of  the  minerals  in  the  soil  usually  provides  enough 
of  the  elements  needed  by  plants,  but  the  supply  of  potassium,  phos- 
phorus and  nitrogen  is  insufficient  for  frequent  repetitions  of  the 
same  crops,  and  the  soil  becomes  less  productive  *  or  barren.  To 
supply  this  yearly  drain  on  the  soil,  fertilizers  are  employed.  The 
natural  fertilizers,  barn-yard  manure,  urine,  and  decomposing  vege- 
table mould  or  muck,  need  little  or  no  treatment  before  use,  and  will 
not  be  considered  here. 

Artificial  fertilizers  are  manurial  substances  prepared  from  mate- 
rials needing  special  treatment  to  render  them  fit  for  plant  food.  The 
chief  requisites  for  a  good  artificial  fertilizer  are:  It  must  contain 
at  least  one  substance  fit  for  plant  food,  and  which  is  easily  converted 
by  rain  or  moisture  into  a  form  that  plants  can  assimilate ;  it  must  be 
dry  and  finely  pulverized,  for  even  distribution  over  the  surface  of  the 
ground ;  nothing  injurious  to  plant  life  may  be  present. 

A  complete  fertilizer  supplies  the  three  essentials,  potassium, 
nitrogen,  and  phosphorus.  Often  only  one  or  two  of  these  elements 
may  be  afforded,  the  fertilizer  being  intended  for  use  with  certain 
crops  or  on  particular  soils.  . 

Potassium  is  generally  returned  to  the  soil  in  the  form  of  sul- 
phate or  carbonate  (wood  ashes),  and  occasionally  as  chloride.  The 
preparation  and  use  of  these  salts  have  already  been  considered  and 
also  the  preparation  of  ground  kainite  (p.  161)  for  this  purpose. 

Nitrogen  is  frequently  supplied  as  ammonium  salts  (p.  154),  or 
nitrates,  particularly  sodium  nitrate  (p.  145).  But  many  substances 
used  for  fertilizers  contain  nitrogen  in  organic  compounds,  which 
decompose  readily  in  the  soil,  setting  free  the  nitrogen. 

Recently  calcium  cyanamid  f  (CaCN2),  made  by  treating  calcium 

*  Loss  of  fertility  may  be  due  to  other  causes  then  depletion  of  plant  food  :  there 
is  some  evidence"  that  plants  leave  deleterious  excretions  in  the  soil,  which  for  a 
time  act  toxically  upon  the  same  variety  of  plant. 

t  Zeitschr.  angew.  Chem.,  1903  (16),  536 ;  1910  (23),  2405. 
J.  Soc.  Chem.  Ind.,  1903,  809. 

Electrochem.  Met.  Ind.,  1907,  77;  1908,  341 ;  1910,  539;  1915,  213. 

164 


FERTILIZERS  165 

carbide  at  1000°  C.  with  nitrogen  gas  from  liquid  air  (p.  267),  has 
come  into  use  as  a  nitrogenous  fertilizer  under  the  name  "  nitrolim" 

Phosphorus  is  nearly  always  applied  to  the  soil  in  some  form  of 
calcium  phosphate  derived  from  mineral  sources  or  from  organic 
matter. 

Fertilizers  are  largely  made  from  the  waste  products  of  slaughter 
houses,  such  as  blood,  bits  of  waste  meat  and  other  refuse,  bones, 
hoofs,  horns,  and  hair.  Tainted  meat  and  animals  which  have  died 
of  disease  are  also  sent  to  the  rendering  tanks.*  Blood  is  dried  at  a 
moderate  heat  and  crushed  to  powder  between  rolls.  It  contains 
about  10  per  cent  N,  and  is  very  uniform  in  composition. 

Raw  bones  contain  fatty  matter  which  is  slow  to  decompose ;  but 
if  allowed  to  ferment  in  compost  heaps  with  wood  ashes  and  stable 
manure  for  a  few  months,  they  become  more  active  and  yield  3  to 
4  per  cent  nitrogen,  as  well  as  20  to  25  per  cent  phosphate.  As  a  rule 
bones  are  extracted  with  superheated  steam  to  remove  the  fat  and 
gelatine,  and  then  ground  to  yield  "  bone  meal,"  carrying  about  27 
to  28  per  cent  of  phosphoric  acid.  This  is  much  more  active  as  a 
fertilizer  than  the  crushed  raw  bones.  Steaming  reduces  the  nitrogen 
to  about  1  to  2  per  cent,  and  makes  the  bone  more  easily  decomposed 
in  the  soil.  If  treated  with  sulphuric  acid,  the  nitrogen  and  phosphoric 
acid  are  rendered  more  available  and  the  product  is  called  "  dis- 
solved bone." 

Bones  are  often  subjected  to  destructive  distillation  in  retorts, 
by  which  nearly  all  the  nitrogen  is  driven  out  as  ammonia,  ammo- 
nium carbonate,  pyridine,  and  other  nitrogenous  organic  compounds, 
while  the  residue  left  in  the  retort,  known  as  "  bone-char  "  or  "  bone- 
black,"  contains  calcium  phosphates  and  other  salts,  mixed  with 
carbon.  This  bone-char  is  extensively  used  as  a  decolorizing  agent 
in  the  purification  of  sugar,  glucose,  oils,  and  other  liquids ;  when  it 
can  no  longer  be  employed  for  this  purpose  (see  p.  311),  it  is  burned 
with  free  access  of  air  to  form  "  white-ash,"  which  contains  a  high 
percentage  of  phosphorus.  This  bone-ash  may  be  used  directly  as  a 
fertilizer,  but  is  usually  treated  with  sulphuric  acid  to  form  "  super- 
phosphate "  (p.  169),  which  is  more  soluble  than  the  tricalcium 
phosphate  of  the  bone. 

A  process  for  extracting  the  mineral  phosphate  from  bones  by 
digesting  with  hydrochloric  acid  has  been  practised  to  some  extent. 

*  "  Rendering  "  consists  in  extracting  all  the  fats,  oils,  and  gelatinous  matter 
from  the  carcasses  by  treating  with  benzine  or  steam  under  pressure.  The  fat 
extracted  is  used  for  soap  stock.  The  dried  residue,  called  "  tankage,"  is  ground 
fine  for  fertilizer,  and  furnishes  both  nitrogen  and  phosphoric  acid. 


166  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

The  solution  of  phosphoric  acid  thus  obtained  is  neutralized  with 
milk  of  lime,  by  which  the  calcium  phosphate  is  precipitated,  chiefly 
as  dicalcium  phosphate  (Ca2H2P2Og).  This  is  sometimes  sold  as 
"  precipitated  phosphate,"  but  the  method  is  more  commonly  applied 
to  low  grades  of  mineral  phosphates  (p.  171)  than  to  bones. 

Garbage  containing  fatty  matter  is  now  collected  in  many  cities 
and  subjected  to  a  rendering  process.  It  is  put  into  steel  digesters 
and  subjected  to  the  action  of  steam  at  50  pounds  pressure  for  eight 
or  ten  hours,  when  the  mass  is  reduced  to  a  soft  pulp  which  is  put  into 
presses  and  the  oily  matter  pressed  out.  The  press-cake  is  broken 
up  and  dried  in  revolving  steam-heated  drums,  after  which  it  is 
powdered,  sifted,  and  used  for  "  filler  "  in  fertilizers,  under  the  name 
"  tankage."  *  It  contains  nitrogen,  phosphoric  acid,  and  a  little 
potash.  On  cooling,  the  oily  matter  forms  a  soft  grease,  which  is  used 
for  soap  and  candle  stock.  The  water  which  is  pressed  out  of  the 
tankage  with  the  grease  contains  a  large  amount  of  ammonium  salts 
and  some  potash ;  it  is  evaporated  to  dryness  and  the  residue  mixed 
with  the  tankage,  thus  increasing  the  nitrogen  and  potash  in  the 
latter. 

Other  nitrogenous  wastes  from  various  industries  —  leather  scrap, 
wool  waste,  and  dust  from  shoddy  and  felt  mills  —  are  used  to  some 
extent;  but  these,  though  very  rich  in  nitrogen,  are  very  slow  in 
decomposing,  and  are  so  light  when  powdered  that  they  are  easily 
blown  away. 

The  press-cakes  from  various  oil  industries  (e.g.  the  manufacture 
of  cotton-seed,  rape,  and  castor  oils)  are  often  ground  for  fertilizer. 
Sometimes  the  cake  is  burned  for  fuel  and  the  ashes  used  for  fertiliz- 
ing, but  in  this  case  the  nitrogen  is  lost,  only  the  potassium  and 
phosphorus  being  returned  to  the  soil.  In  the  manufacture  of  fish 
oils  there  is  a  considerable  amount  of  residue  from  which  the  oil  has 
been  pressed  (p.  363).  This  is  known  as  "  fish  scrap,"  and  consists 
of  the  scales,  bones,  fins,  and  meat  of  the  fish.  It  contains  about  7 
per  cent  of  nitrogen  and  nearly  16  per  cent  of  phosphorus  pentoxide 
(P2O5).  Dried  (usually  by  exposure  to  the  sun)  and  crushed  to  a 
rather  coarse  powder,  it  is  a  valuable  fertilizer,  decaying  rapidly  in 
the  soil. 

Peruvian  guano,  formerly  of  great  importance  as  a  fertilizer,  but 

the  beds  now  nearly  exhausted,  consists  of  dried  excrement,  feathers, 

and  carcasses  of  sea  fowl,  and  is  rich  in  nitrogen  and  phosphoric 

acid.     It  is  found  in  certain  islands  near  the  coast  of  Peru  and  Chili, 

*  This  term  is  also  applied  to  the  dried  residues  of  various  rendering  processes. 


FERTILIZERS  167 

and  also  on  the  mainland  at  the  base  of  the  Andes,  near  the  sodium 
nitrate  beds  (p.  145).  The  region  is  dry  and  hot,  and  the  guano 
has  been  preserved  with  a  high  percentage  of  nitrogen,  largely  as 
uric  acid  and  its.  salts.  It  needs  no  preliminary  treatment  before 
spreading  on  the  soil.  Fresh  guano,  from  various  islands  in  the 
South  Pacific,  is  damp,  and  contains  much  ammonium  carbonate; 
this  must  be  "  fixed  "  by  mixing  with  sulphuric  acid,  to  prevent  loss 
of  the  nitrogen. 

Fossil  guanos,  consisting  of  fossil  excrement  and  remains  of  birds 
and  reptiles,  are  found  in  the  West  Indies,  Bolivia,  Chili,  and  the 
South  Pacific  islands.  Since  more  or  less  rain  falls  in  these  climates, 
the  soluble  ammonium  salts  and  nitrates  have  been  washed  out, 
leaving  only  the  calcium  phosphate.  Some  of  these  guanos  have 
entered  into  combination  with  the  rocks  on  which  they  were  de- 
posited, thus  altering  their  original  character  considerably ;  e.g.  some 
of  them  contain  a  large  amount  of  calcium  sulphate.  Fossil  guanos 
are  prepared  in  the  same  way  as  phosphate  rock  (see  below). 

Phosphoric  acid  is  chiefly  supplied  by  phosphate  rocks,  such  as 
apatite,  or  phosphorite,  found  in  large  deposits  in  Belgium,  Germany, 
France,  Spain,  Algiers,  Canada,  South  Carolina,  Florida,  Tennessee. 
Arkansas,  Montana,  Wyoming,  Idaho,  Utah,  the  West  Indies,  and 
certain  islands  in  the  Pacific  and  Indian  oceans.  At  present  the 
United  States  deposits  are  the  most  important. 

Apatite  [3  Ca3P2O8  +  CaF2  •  (CaCl2)]  is  a  crystalline  mineral, 
occurring  in  large  deposits  in  Canada  and  Spain.  The  former  are 
very  extensive,  and  are  found  in  Ontario,  between  the  St.  Lawrence 
and  Ottawa  rivers,  and  in  Quebec  Province,  along  the  Gatineau 
and  du  Lievre  rivers.  The  mineral  sometimes  occurs  in  veins  and 
pockets  (bonanzas)  of  nearly  pure,  massive  apatite;  and  in  other 
cases  as  distinct,  hexagonal  crystals  or  nodules,  disseminated  in 
calcite  or  pyroxene.  The  material  is  sold  on  a  guarantee  of  75  or 
80  per  cent  of  calcium  phosphate,  and  to  secure  this  degree  of  purity, 
"  cobbing  "  *  and  hand-picking  must  be  employed.  The  ore  being 
exceedingly  brittle  and  the  gangue  rock  hard,  there  is  much  loss  in 
the  "  fines,"  from  which  it  is  not  profitable  to  separate  the  phosphate 
rock. 

Apatite  varies  in  character  from  a  moderately  hard  rock  to  a  soft 

and  friable  mass,  called  "  sugar."     The  color  varies  much,  but  is 

generally  blue-green  or  red-brown.     The  tricalcium  phosphate  being 

quite  insoluble,  the  mineral  must  be  treated  with  sulphuric  acid  to 

*  Breaking  the  large  lumps  with  hammers  by  hand. 


168  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

form  "  superphosphate."  But  since  more  or  less  calcium  fluoride 
and  chloride  are  present,  considerable  acid  is  uselessly  consumed,  and 
a  special  condensing  apparatus  is  necessary  to  retain  the  vapors  of 
hydrofluoric  and  hydrochloric  acids  set  free,  or  a  nuisance  is  created. 
Apatite  also  requires  a  rather  strong  acid  (1.78  sp.  gr.)  for  its  decom- 
position, while  the  calcite  and  other  minerals  connected  with  it,  being 
acted  upon,  cause  considerable  loss  of  acid. 

These  objections  do  not  apply  to  the  phosphorites  of  the  United 
States  and  Europe,  and  the  cost  of  mining  is  not  so  great.  As  a  re- 
sult the  use  of  apatite  for  fertilizer  making  has  ceased. 

Phosphorites  are  amorphous  rocks  of  varying  composition,  but  all 
containing  a  large  percentage  of  tricalcium  phosphate,  and  some- 
times iron  and  aluminum  phosphates.  The  mode  of  formation  of 
these  rocks  has  been  a  much-disputed  question,  but  they  are  now 
generally  regarded  as  of  organic,  and  probably  animal  origin.  The 
beds  are  filled  with  fossil  remains  of  land  and  marine  animals  and 
fishes.  A  nodular  variety  found  in  England  was  erroneously  sup- 
posed to  be  fossil  reptilian  excrement,  and  was  called  "  Coprolites." 

Some  phosphorites  are  compact  and  hard  to  grind,  as  is  the 
Spanish  variety,  but  the  American  rock  is  softer  and  porous.  In 
the  United  States  there  are  two  varieties,  "  land  rock  "  and  "  river 
rock." 

Land  rock  occurs  in  beds  averaging  from  10  to  12  inches  in  thick- 
ness, and  from  2  to  40  feet  below  the  surface  of  the  ground.  These 
beds  are  sometimes  composed  of  loose  pebbles  or  gravel,  but  frequently 
these  have  been  compacted  into  solid  layers  having  a  laminated  struc- 
ture; or  they  may  form  great  boulders  or  conglomerate  masses. 
The  beds  are  often  continuous  over  a  large  area,  but  "  pockets  "  or 
isolated  beds  are  frequently  found.  Good  rock  will  average  from 
75  to  80  per  cent  of  tricalcium  phosphate  (CazPzOs).  In  some  cases 
the  land  rock  is  hard,  dense,  and  nearly  pure  (hard  phosphate),  while 
in  others  it  is  soft,  resembling  clay  in  its  consistency,  and  usually 
containing  rather  a  large  proportion  of  iron  and  aluminum. 

Land  rock  is  mined  by  stripping  off  the  overlying  earth,  and 
digging  out  the  phosphate  rock  with  pick  and  shovel.  It  has  been 
found  practical  to  use  steam  shovels  and  dredges  for  "  soft  phosphate  " 
and  "  pebble  "  deposits.  In  compact  rock,  blasting  is  necessary. 
The  work  is  done  in  open  pits,  tunnelling  not  having  proved  success- 
ful. The  depth  of  overburden  which  may  be  profitably  removed 
depends  upon  the  thickness  and  purity  of  the  deposit,  but  about 
20  feet  is  the  limit,  except  in  the  case  of  very  thick  beds  of  high-grade 


FERTILIZERS  169 

ore.  For  ordinary  rock,  the  limit  is  about  10  or  12  feet.  In  a  few 
cases  hydraulic  mining  has  been  employed  to  wash  away  the  over- 
burden. 

After  mining,  the  rock  is  put  through  a  "  breaker,"  and  reduced 
to  lumps  about  4  inches  in  diameter.  These  go  to  the  "  washer," 
which  consists  of  a  long,  semicircular  trough,  set  at  a  slight  incline, 
in  which  there  is  a  revolving  shaft,  carrying  teeth  or  blades  about 
9  inches  long,  and  arranged  around  it  in  the  form  of  a  spiral  screw, 
having  a  pitch  of  about  1  in  6.  The  trough  is  set  in  a  tank  of  water, 
or  a  large  stream  of  water  enters  at  the  upper  end.  The  lumps  of 
rock  are  fed  into  the  trough  at  the  lower  end,  and  being  caught  by 
the  teeth,  are  forced  along  and  up  the  trough,  against  the  water.  The 
rubbing  against  each  other  and  the  action  of  the  water  wash  away 
the  sand  and  clay,  and  at  the  upper  end  the  clean  rock  falls  on  screens, 
which  separate  the  several  sizes  of  lumps.  It  is  usually  dried  by  pil- 
ing it  on  racks  of  cord  wood,  which  are  then  fired  and  allowed  to  burn 
out ;  or  it  may  be  piled  over  cast-iron  pipes  having  numerous  aper- 
tures through  which  hot  air  from  a  furnace  is  forced.  The  rock  is 
then  shipped  to  the  makers  of  "  superphosphate." 

River  rock  is  dredged  or  dug  from  the  beds  of  rivers  and  streams, 
especially  Peace  River  and  its  tributaries  in  Florida,  and  from  the 
streams  near  Charleston  and  Beaufort,  S.C.  When  the  deposit 
is  in  the  form  of  loose  nodules  and  gravel,  steam  dredges  or  cen- 
trifugal pumps  are  used  to  raise  it;  but  when  it  is  compact  rock, 
special  forms  of  grips  and  dredges  are  necessary.  In  most  cases, 
river  mining  is  not  carried  on  in  water  more  than  30  feet  deep. 

River  rock  is  very  similar  in  composition  to  land  rock,  but  is 
darker  in  color,  even  black,  and  contains  more  animal  remains  and 
fossils.  It  is  preferred  by  foreign  superphosphate  makers  and  is 
generally  shipped  abroad. 

"  Superphosphate  "  is  the  name  given  to  a  soluble  phosphate,  pre- 
pared by  treating  insoluble  rock  or  bone  *  phosphate,  with  sulphuric 
acid.  By  the  action  of  the  acid,  the  insoluble  tricalcium  phosphate 
is  converted  into  monocalcium  phosphate  (CaH4P2O8),  while  in 
many  cases  some  free  phosphoric  acid  is  also  formed. 

The  reactions  involved  are  as  follows :  — 

1)  Ca3P2O8  +  2  H2SO4  +  4  H2O  =  CaH4P2O8  +  2  (CaSO4  •  2  H2O). 

2)  Ca3P2O8  +  3  H2S04  +  6  H2O  =  2  H3PO4  +  3  (CaSO4  •  2  H2O). 

3)  Ca3P2O8  +  H2S04  +  4  H20  =  (Ca2H2P2O8  -  2  H2O)  +  (CaSO4  •  2  H2O). 

*  Superphosphate  made  from  bones  contains  some  nitrogen  as  well  as  phosphoric 
acid. 


170  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

Reactions  (1)  and  (2)  are  the  ones  desired  in  fertilizer  making,  but 
if  too  little  acid  is  used,  reaction  (3)  takes  place  to  a  greater  or  less 
extent,  forming  dicalcium  phosphate,  which  is  also  insoluble.  If 
too  much  acid  is  used,  reaction  (2)  takes  place  to  an  undesirable  ex- 
tent, and  the  product  contains  an  excess  of  free  phosphoric  acid, 
which  attracts  moisture  from  the  air,  making  the  fertilizer  moist 
and  lumpy.  A  small  excess  of  acid  over  the  theoretical  quantity 
needed  is  generally  used  to  prevent  "reversion"  (below)  as  far  as 
possible.  The  proper  regulation  of  the  amount  of  acid  requires 
great  care,  and  must  be  controlled  by  analysis  of  the  material.  The 
acid  employed  is  "chamber  acid  "  of  1.54  to  1.60  sp.  gr.  Concen- 
trated acid  is  not  used,  because  water  is  necessary  in  order  that  a 
hydrated  calcium  sulphate  may  be  formed.  The  formation  of  the 
gypsum  (CaSO4  •  2  H2O)  aids  in  the  subsequent  drying  of  the  product. 

Hydrochloric  acid  is  unsuitable  for  fertilizer  making,  because  of 
its  expense,  and  the  formation  of  calcium  chloride  in  the  product. 
The  raw  phosphate  should  be  as  free  as  possible  from  impurities, 
such  as  carbonates,  iron  oxide,  and  alumina.  About  3  per  cent  of 
Fe2O3  +  A12O3  is  the  limit  now  allowed. 

The  phosphate  rock,  ground  in  Griffin,  Kent,  or  ball  mills  (p.  188) 
to  pass  a  60-  or  80-mesh  sieve,  is  put,  with  the  required  amount  of 
acid,  into  a  cast-iron  mixer,  provided  with  a  stirring  device.  The 
mixing  is  complete  in  two  to  five  minutes,  when  the  slimy  mass  is  at 
once  run  into  a  brick-lined  "  pit  "  or  "  den,"  where  the  reactions 
take  place.  The  temperature  rises  to  100°  or  110°  C.,  and  much  fume 
(HF,  SiF4,  CO2)  escapes.  As  the  reactions  progress,  the  charge  stiffens 
and  finally  solidifies  into  a  porous  dry  mass.  Successive  charges  from 
the  mixer  are  dumped  into  the  "  den  "  until  it  is  filled ;  then  the  whole 
is  left  quiet  for  some  days  or  weeks,  for  the  reactions  to  end.  The 
product  is  then  dug  out  of  the  pit,  pulverized  in  a  disintegrator,  where 
nitrogenous  or  potash  materials  may  be  added  if  desired,  and  packed 
in  bags  for  market. 

If  the  phosphate  rock  contains  much  iron  or  aluminum  oxide,  or 
if  the  decomposition  by  acid  has  been  incomplete,  a  series  of  sec- 
ondary reactions  ensues  when  the  superphosphate  is  stored.  By 
these,  a  part  or  all  of  the  monocalcium  phosphate  (CaH4P2O8)  and 
the  free  phosphoric  acid  may  be  converted  into  the  insoluble  di- 
calcium phosphate,  or  into  insoluble  phosphates  of  iron  or  aluminum. 
This  constitutes  "  reversion,"  and  the  insoluble  calcium  or  iron 
phosphates  so  formed  are  called  "  reverted  phosphate."  Since 
fertilizer  is  valued  according  to  its  percentage  of  soluble  phosphate, 


FERTILIZERS  171 

reversion  is  a  serious  matter  for  manufacturer  and  buyer.  Reverted 
phosphate  is  recognized  as  having  value  for  fertilizer  purposes,  but 
less  than  superphosphate. 

When  due  to  incomplete  decomposition  of  the  rock,  reversion 
takes  place  according  to  the  following  reaction  :  — 

CaH4P2O8  +  Ca3P2O8  =  2  Ca2H2P2O8. 

When  the  rock  contains  iron  or  alumina,  the  temperature  of  the 
reaction  in  the  pit  is  kept  as  low  as  possible,  to  prevent  combina- 
tion between  these  oxides  and  the  free  phosphoric  acid  formed.  It 
is  customary  in  this  case  to  remove  the  superphosphate  from  the  pit 
as  soon  as  it  solidifies,  and  to  cool  it  by  exposure  to  the  air. 

A  "  double  superphosphate  "  is  also  made,  in  Europe,  and  contains 
more  soluble  phosphoric  acid  than  the  ordinary  superphosphate. 
A  quantity  of  bones  or  phosphate  rock  is  'decomposed  with  sufficient 
dilute  sulphuric  acid  to  set  free  all  the  phosphoric  acid  and  precipi- 
tate all  the  calcium  as  hydrated  calcium  sulphate.  The  precipitate 
is  removed  by  the  filter  press  (p.  15),  and  the  clear  solution  of  phos- 
phoric acid  is  concentrated  by  surface  heating  in  lead  pans,  to  a  den- 
sity of  45°  Be.,  at  which  strength  the  solution  contains  nearly  45  per 
cent  P2O5.  During  concentration,  the  iron  and  aluminum  phos- 
phates separate  and  are  removed.  The  strong  solution  of  phosphoric 
acid  is  then  treated  with  ground  phosphate  rock,  in  proper  quantity 
to  form  monocalcium  phosphate,  which  is  dried  and  disintegrated. 
The  reactions  are  as  follows  :  — 

1)  Ca3P2O8  +  3  H2SO4  +  6  H2O  =  3(CaSO4  •  2  H2O)  +  2 

2)  Ca3P2O8  +  4  HaP04=  3 


By  this  process,  a  very  concentrated  fertilizer,  containing  no 
gypsum  or  other  sulphate,  is  obtained.  Moreover,  a  low-grade  phos- 
phate rock,  which  would  not  furnish  a  strong  fertilizer  with  sulphuric 
acid,  can  be  used  for  making  the  phosphoric  acid. 

Phosphate  rock  is  also  used  directly  for  fertilizer,  without  other 
preparation  than  fine  grinding.  But  tricalcium  phosphate,  being  in- 
soluble, is  only  slowly  assimilated  by  plants,  and  its  action  is  not  very 
marked.  Several  years  are  necessary  for  its  complete  decomposition. 

Phosphatic  slag  is  now  used  to  a  considerable  extent  as  a  fertil- 
izer, especially  in  Europe.  In  the  process  of  making  Bessemer  steel 
by  the  Thomas  and  Gilchrist  method,  pig  iron  from  ores  containing 
phosphorus  is  .treated  with  an  excess  of  lime  in  a  Bessemer  con- 
verter, lined  with  lime,  while  a  blast  of  air  is  forced  into  the  liquid 


172  OUTLINES   OP   INDUSTRIAL   CHEMISTRY 

mass.  At  the  high  temperature  of  the  melted  iron,  the  phosphorus 
is  oxidized  to  pentoxide,  which  combines  with  the  lime.  The  silica, 
alumnia,  lime,  and  magnesia  unite  to  form  a  slag,  into  which  the 
calcium  phosphate  produced  also  goes.  By  proper  regulation  of  the 
charge,  a  slag  containing  about  17  per  cent  of  pentoxide  (PzO^)  is 
obtained.  The  phosphate  in  the  slag  is  supposed  to  be  a  tetracalcic 
phosphate  (Ca4P2O9),  which  is  insoluble  in  water,  but  is  much  less 
stable  than  tricalcium  phosphate.  When  exposed  to  the  weather  in 
the  soil,  it  decomposes,  though  somewhat  slowly,  and  the  phos- 
phorus passes  into  a  form  which  plants  can  assimilate.  In  order 
that  this  decomposition  may  take  place,  the  slag  must  be  ground 
very  fine,  so  that  90  per  cent  of  it  will  pass  through  a  sieve  with 
100  meshes  to  the  linear  inch.  The  grinding  is  best  done  in  a  ball 
mill  (p.  187). 

Slag  fertilizer  needs  no  further  treatment  than  very  fine  grind- 
ing, but  it  is  slow  in  decomposing,  and  its  full  effect  is  not  obtained 
for  two  or  three  years.  It  decomposes  more  rapidly  than  ground 
phosphate  rock,  however,  and  is  cheap. 

There  has  been  considerable  controversy  among  agricultural 
chemists  as  to  the  relative  value  of  soluble  and  insoluble  phosphates. 
Some  hold  that  the  soluble  phosphate  is  at  once  converted  into  the 
insoluble  form  when  it  comes  into  contact  with  the  lime,  alumina, 
and  iron  in  the  soil ;  and  that  this  insoluble  phosphate  is  dissolved 
or  absorbed  by  the  sap  in  the  plant  roots,  the  sap  presumably  having 
an  acid  nature.  Other  chemists  claim  that  only  the  soluble  phos- 
phate, as  such,  can  be  taken  up  by  the  plant.  It  appears  from  ob- 
served facts  that  both  soluble  and  insoluble  phosphates  are  taken 
up  by  the  plant,  but  the  nature  of  the  soil  is  an  important  factor. 
On  a  soil  poor  in  lime,  and  containing  some  organic  matter,  insoluble 
phosphates  produce  their  best  results ;  but  if  the  soil  contains  much 
lime,  then  the  superphosphate  appears  to  have  the  advantage. 

The  soluble  character  of  the  superphosphate  permits  its  dif- 
fusion through  the  soil  by  rain,  so  that  it  is  brought  immediately 
to  the  roots  of  the  plants.  But  the  insoluble  phosphate  must  be 
turned  under  the  soil,  and  the  roots  grow  to  it ;  then,  too,  when  not 
finely  ground,  it  possesses  but  little  value,  owing  to  the  slow  decom- 
position ;  but  when  in  a  very  fine  powder,  it  is  taken  up  in  some  way 
by  the  roots  of  the  plant  with  fair  rapidity. 

The  manufacture  and  sale  of  artificial  fertilizers  are,  to  a  certain 
extent,  under  legal  restriction  in  nearly  all  the  states.  To  prevent 
fraud,  manufacturers  are  required  to  take  out  a  license,  and  to  sub- 


FERTILIZERS  173 

mit  samples  for  analysis  by  state  chemists;    frequently  a  guarantee 
of  the  stated  composition  is  required. 

The  methods  of  analyses  of  fertilizers  are  set  forth  in  detail  in  the 
bulletins  of  the  several  state  agricultural  experiment  stations  and  of  the 
United  States  Department  of  Agriculture.*  In  general  the  matter  de- 
termined by  the  analysis  may  be  summed  up  as :  — 

(a)  Water,  both  hygroscopic  and  combined. 

(6)  Total  phosphoric  acid. 

(c)  Soluble  phosphoric  acid. 

(d)  Reverted  phosphoric  acid. 

(e)  Total  nitrogen. 
(/)  Potash. 

Another  substance  frequently  sold  as  fertilizer  is  pulverized 
gypsum  (CaSO4  •  2  H2O),  which,  when  crushed  to  a  fine  powder,  is 
brought  into  commerce  under  the  name  of  "  plaster."  As  a  fertil- 
izer it  is  of  little  value,  except  in  soils  poor  in  lime  or  those  contain- 
ing "black  alkali"  (sodium  carbonate).  But  it  is  also  claimed  to 
have  a  beneficial  action  in  retaining  nitrogen  in  the  soil.  The  cal- 
cium sulphate  is  supposed  to  be  decomposed  by  the  ammonia  and 
carbonic  acid  from  the  air  and  rain,  forming  ammonium  sulphate 
and  calcium  carbonate.  Ammonium  sulphate  furnishes  nitrogen  in 
a  form  which  plants  can  assimilate. 

Much  attention  has  been  devoted,  especially  in  Germany,  to 
methods  of  recovering  fertilizing  material  from  the  sewage  of  cities. 
But  when  closets  are  flushed  with  water,  the  effluent  is  generally  too 
dilute  to  be  worth  recovering.  It  is,  however,  used  to  some  extent, 
in  irrigating  lands,  generally  those  owned  by  the  municipality.  Sew- 
age is  often  precipitated  with  lime  or  other  substance,  but  this  gen- 
erally renders  the  sludge  useless  for  fertilizing.  The  contents  of  dry 
vaults  or  cesspools  are  collected  at  regular  intervals  and  used  for 
fertilizing. 

But  sewage  treatment  of  any  kind  is  usually  practised  to  pre- 
vent pollution  and  unsanitary  conditions  in  the  streams  and  water 
supplies,  rather  than  for  the  utilization  of  the  fertilizing  materials 
to  be  obtained. 

REFERENCES 

Lehrbuch  der  Diingerfabrication.     Paul  Wagner.     Braunschweig,  1877. 
Report  of  the  Commissioner  of  Agriculture  of  South  Carolina,  for  the  year 

1880.     Chas.  U.  Shepard. 

Bulletin  de  la  Societe  Chimique,  1884,  219.     E.  Dreyfus. 
Die  kiinstlichen  Dungermittel.    Dr.  S.  Pick,  Leipzig,  1887.     (Hartleben.) 

*  Bull.  No.  28,  U.  S.  Dept.  Agriculture ;   Division  of  Chemistry. 


174  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

The  Nature  and  Origin  of  Deposits  of  Phosphate  of  Lime.  R.  A.  F.  Pen- 
rose,  Bull.  46,  U.  S.  Geological  Survey,  Washington,  1888. 

A  Treatise  on  Manures.     A.  B.  Griffiths,  London,  1889.     (Bell  and  Sons.) 

The  Phosphates  of  America.     Francis  Wyatt,  New  York,  1891. 

Florida,  South  Carolina,  and  Canadian  Phosphates.  C.  C.  Hoyer  Millar, 
London,  1892.  (Fischer  and  Co.) 

Les  Phosphates  de  Chaux  naturels.     Paul  Hubert,  Paris,  1893. 

The  Phosphate  Industry  of  the  United  States.  Carroll  D.  Wright, 
Washington,  1893.  (Sixth  Special  Report  of  the  U.  S.  Commissioner 
of  Labor.) 

J.  Amer.  Chem.  Soc.,  1893,  321.  C.  U.  Shepard.  1895,  47.  W.  E. 
Garrigues. 

J.  Soc.  Chem.  Ind.,  1888,  79.  W.  T.  MacAdam.  1894,  842.  Kalmann 
and  Meissels. 

Agricultural  Analysis.     H.  W.  Wiley,  2d  ed.,  Vol.   II,  Fertilizers,  1908. 

Die  Superphosphatfabrikation.     Dr.   Ritter  von  Grueber,   Halle,   1907. 

The  Manufacture  of  Chemical  Manures.     J.  Fritsch,  New  York,  1911. 

Fertilizer  Resources  of  the  United  States.  Senate  Document  No.  190, 
62d  Congress.  Washington,  1912. 


LIME,   CEMENT,  AND  PLASTER  OF  PARIS 


Good  lime  is  nearly  pure  calcium  oxide;  it  is  one  of  the  most 
important  substances  used  in  chemical  industry,  and  is  prepared  in 
enormous  quantities  by  calcining  calcium  carbonate  (limestone, 
chalk,  or  the  shells  of  mollusks)  at  a  bright  red  heat.  If  the  carbon- 
ate used  contains  much  silica,  iron,  alumina,  or  other  impurity,  the 
lime  does  not  slake  freely  with  water,  and  is  said  to  be  "  poor  "  or 
"  lean  "  ;  with  but  small  quantities  of  these  impurities  present,  a  fair 
lime  is  produced,  when  properly  burned.  Such  impure  carbonates 
are  difficult  to  burn,  as  slight  overheating  causes  semi-fusion  of  the 
lumps,  and  the  lime  combines  with  water  slowly  and  incompletely, 
and  is  said  to  be  "  burned  to  death."  A  pure  lime,  which  combines 
readily  with  water  to  form  a  fine  white  powder,  free  from  grit,  and 
which  makes  a  smooth  stiff  paste  with  an  excess  of  water,  is  called  a 
"fat  "lime. 

Calcium  carbonate  begins  to  decompose  below  a  red  heat  into 
calcium  oxide  and  carbon  dioxide,  but  the  decomposition  is  not 
complete  until  a  bright  red  heat  (800°  or  900°  C.)  is  reached.  The 
temperature  should  not  rise  much  above  1000°  to  1200°  C.,  as  there 
is  danger  of  overheating  the  lime.  It  is  essential  that  the  gases  es- 
cape freely  from  the  kiln,  the  draught  usually  being  sufficient  to 
remove  them  as  they  form.  This  escape  may  be  accelerated  by  blowing 
steam  or  air  into  the  kiln  during 
the  burning,  or  even  by  wetting 
the  carbonate  as  it  is  introduced. 
If  the  gases  are  retained,  they 
cause  pressure  in  the  kiln  and 
thus  hinder  the  decomposition ; 
and  on  cooling,  the  carbonic  acid 
recombines  with  the  lime. 

Limekilns  are  of  two  classes, 
periodic  and  continuous   (see  p. 
22).     In  this  country,  long-flame, 
periodic  kilns  are  sometimes  used, 
though  they  are  uneconomical  of  ' 
fuel  and  time :  but  they  are  em- 
ployed because  of  simplicity  and  cheapness  of  building.    They  are  made 
of  brick  or  large  stone  blocks,  an  arch  (A,  Fig.  73)  being  turned  two 

175 


176 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


or  three  feet  from  the  ground,  with  numerous  openings  left  for  the  flames 
to  pass  into  the  kiln.  The  fire  burns  under  the  arch,  on  top  of  which 
the  limestone  is  piled,  the  lumps  varying  from  the  size  of  a  cocoanut 
just  above  the  arch,  to  that  of  a  goose  egg  at  the  top  of  the  kiln. 
In  starting  the  kiln  the  temperature  is  slowly  raised  during  six  or  eight 
hours,  to  prevent  the  limestone  arch  from  crumbling ;  then  a  full  red 
heat  is  held  for  two  days  or  more,  when  the  fire  is  allowed  to  burn  out 
and  the  kiln  cools.  During  the  time  of  cooling,  discharging,  and  re- 
charging, the  kiln  stands  idle,  thus  losing  much  time.  Moreover,  a 
large  amount  of  fuel  is  required  to  heat  the  walls  of  the  kiln  after 
each  recharging. 

Continuous  kilns  are  preferred  where  fuel  is  expensive,  and  where 
a  large,  regular  output  is  desired.  They  are  tall  furnaces  (shaft 
kilns),  built  of  brick  or  of  iron  plates,  and 
usually  from  40  to  50  feet  high,  by  6  to  10 
feet  diameter.  The  limestone  is  fed  in  at  the 
top  and  the  lime  taken  out  at  the  bottom 
without  interrupting  the  process.  Vertical 
shaft  kilns  for  mixed  feed  of  fuel  and  lime- 
stone, or  separate  combustion  of  the  fuel,  are 
frequently  used.  The  mixed  feed  kiln  is 
cheaper  to  build  and  operate,  but  yields  a 
product  somewhat  unevenly  burned  and  dis- 
colored. The  separate  combustion  type  is 
commonly  used  at  the  larger  plants,  and  while 
of  lower  fuel  efficiency,  it  yields  clean,  high- 
grade  lime.  Such  a  kiln  (Fig.  74)*  consists 
of  a  steel  shell,  lined  with  fire-brick  (B)  forming 
a  shaft  6|  feet  inside  diameter  and  48  feet 
high.  There  are  four  furnaces  (A),  the  flames 
from  which  enter  the  shaft  at  (D)  and  pass 
up  through  the  limestone  in  the  shaft.  From  the  cooling  cone  (C),  the 
lime  is  dropped  at  intervals  through  the  draw-gate  into  the  car 
below. 

The  separate  combustion  type  of  kiln  works  best  with  a  long- 
flame  combustible,  such  as  wood,  soft  coal,  oil,  or  gas.  Otherwise  the 
only  heat  supply  for  the  reaction  is  from  the  hot  gases  from  the  grate, 
from  which  the  heat  absorption  is  slow.  A  volatile  combustible 
may  be  burned  in  immediate  contact  with  the  charge,  even  within  the 
pores  of  the  lime  itself,  evolving  its  heat  exactly  where  needed.  A 
*  Courtesy  of  Steacy-Schmidt  Manufacturing  Company,  of  York,  Pa. 


FIG.  74. 


LIME,   CEMENT,  AND  PLASTER  OF  PARIS 


177 


recent  improvement*  in  kiln  construction  (Doherty-Eldred  Kiln, 
Fig.  75),  f  is  the  use  of  induced  draft  by  a  fan  drawing  the  gases  from 
the  top  of  the  kiln,  diverting  a  part  of  them 
into  the  air  supply  under  the  grate.  There  the 
carbon  dioxide  is  reduced  to  carbon  monoxide 
by  the  coal,  and  is  later  reoxidized  by  excess 
air  in  the  kiln  itself.  This  secures  a  long- 
flame  action  of  the  combustion,  producing 
uniform  heating,  with  less  destruction  of  the 
furnace  lining  and  less  overburned  lime. 

The  best  fuel  for  lime  burning  is  wood, 
since  it  gives  a  long  flame  of  only  moderate 
heat  intensity;  but  owing  to  its  cost,  other 
fuels,  as  coal,  coke,  oil,  and  natural  and  pro- 
ducer gas,  are  used.  Oil  arid  gas  firing  yields 
very  clean  lime,  burned  at  a  constant  tem- 
perature. To  calcine  one  kilo  of  calcium 
carbonate  requires  425  Cal. :  thus  taking  the 
thermal  value  of  carbon  as  8140  Cal.,  it 
appears  that  each  100  kilos  of  limestone,  or  each  56  kilos  lime  pro- 
425  x  100 


FIG.  75. 


duced,  will  require 


=  5.2  kilos  of  carbon  as  fuel.      This 


8140 

takes  no  account  of  the  fuel  needed  to  heat  the  limestone  to  the 
temperature  of  dissociation,  nor  of  losses  by  radiation  and  conduc- 
tion in  the  burning.  In  practice,  for  each  100  kilos  of  lime  produced, 
the  kilns  consume  from  16  to  20  kilos  of  good  coal,  and  with  periodic 
kilns  this  may  be  nearly  doubled. 

Excepting  the  limekilns  in  the  ammonia-soda  works,  no  attempt, 
as  a  rule,  is  made  to  save  the  carbonic  acid  gas  which  escapes  from  the 
top  of  the  kiln.  But  in  Europe  the  gas  is  often  collected  and  used  for 
technical  purposes. 

Freshly  burned  lime  is  called  "  caustic  "  lime,  or  "  quicklime," 
because  of  its  corrosive  action  on  organic  matter.  When  pure,  it 
is  white  and  amorphous,  but  iron  gives  it  a  yellow  tint.  The  crys- 
talline limestones  and  pure  marble  yield  the  best  lime.  Owing  to 
the  loss  of  water,  organic  matter,  and  carbon  dioxide  during  the 
burning,  there  is  great  reduction  in  the  weight  of  the  charge,  but  only 
a  slight  decrease  in  its  volume.  As  a  rule,  100  pounds  of  good  lime- 

*  This  is  an  application  of  the  Eldred  combustion  process.  Eng.  Pat.  17,197 
of  1901.  Jour.  Soc.  Chem.  Ind.,  1902,  696. 

t  Catalogue  of  the  Improved  Equipment  Co.,  of  New  York. 

N 


178  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

stone  yield  about  56  pounds  of  lime,  but  the  shrinkage  in  bulk  is  not 
over  10  to  20  per  cent  of  the  original  volume  of  the  stone.  The 
hardness  decreases  and  the  lime  is  much  more  porous  than  the  lime- 
stone, absorbing  considerable  water  before  slaking.  Lime  has  great 
affinity  for  water,  and  when  wet  the  lumps  expand  and  fall  to  powder 
of  calcium  hydroxide  (slaked  lime),  with  the  evolution  of  much  heat, 
especially  in  the  case  of  "  fat  lime."  When  exposed  to  the  air,  lime 
absorbs  carbon  dioxide  and  moisture,  and  soon  falls  to  a  powder  called 
"  air-slaked  lime,"  consisting  of  a  mixture  of  calcium  carbonate  and 
hydroxide.  Lime  for  mortar  and  other  purposes  is  generally  slaked 
immediately  before  use.  Pure  lime  is  infusible  at  the  temperature 
of  the  oxy hydrogen  flame  (hence  its  use  in  the  "calcium  light"), 
but  if  silica,  iron,  alumina,  or  other  impurity  is  present,  the  lime 
combines  with  it  to  form  a  slag  or  glass.  Lime  is  a  powerful  base  and 
combines  with  acids  to  form  calcium  salts. 

Magnesium  carbonate  is  a  common  associate  of  limestone,  but 
if  there  is  not  more  than  5  per  cent  of  magnesia  present,  the 
burned  product  is  called  a  high-calcium  lime ;  if  30  per  cent  or  more 
magnesia  is  present,  the  lime  is  "  high-magnesium  "  lime.  Dolomite 
(CaCO3  •  MgCO3)  and  high-magnesian  limestones  generally  appear 
to  dissociate  at  lower  temperatures  *  than  do  the  pure  limestones. 
Magriesian  limes  slake  slowly  and  with  less  heat  evolution  than  pure 
lime,  and  they  make  a  stiffer  mortar  paste. 

Certain  siliceous  or  argillaceous  limestones  yield  a  product,  upon 
burning,  which  slakes  and  falls  to  powder  when  treated  with  water ; 
but  after  a  time  the  pulverized  mass  becomes  hard  and  rocklike 
through  further  action  of  the  water  upon  the  calcium  silicates  or 
aluminates,  produced  during  the  burning.  Such  lime  is  called  "  hy- 
draulic lime  "  and  forms  an  intermediate  link  between  the  common 
limes  and  the  true  cements.  The  calcination  is  conducted  at  medium 
temperature  but  high  enough  to  cause  combination  between  some  of 
the  calcium  oxide  with  nearly  all  of  the  silica  and  alumina,  and  still 
leave  enough  free  lime  to  slake  the  clinkered  material.  Limestone 
suitable  for  hydraulic  lime  usually  contains  from  70  to  80  per  cent  of 
calcium  carbonate,  with  12  to  17  per  cent  of  silica,  and  less  than  3  per 
cent  of  alumina  and  iron  together.  Hydraulic  limes  are  chiefly  em- 
ployed in  mortar  and  cement  mixtures. 

Since  much  heat  is  liberated  in  the  slaking  of  lime,  the  storage 
and  shipment  are  attended  with  some  danger.  If  water  comes  into 
contact  with  the  lime  in  presence  of  combustible  material,  fire  is  very 
apt  to  ensue. 

*  Probably  about  600  to  700°  C.  (Eckel). 


LIME,   CEMENT,   AND   PLASTER  OF  PARIS  179 

Hydrated  lime,  slaked  with  just  the  proper  quantity  of  water  to 
yield  a  dry  fine  powder,  is  prepared  commercially.  The  crushed 
lime  is  slaked  in  mechanical  hydrators,  sometimes  of  a  form  similar 
to  the  chlorine  absorber  (Fig.  63).  The  water  and  lime  enter  the  top 
cylinder  in  measured  amounts,  and  the  hydration  proceeds  to  com- 
pletion. Batch  hydrators,  consisting  of  a  revolving  pan  with  ploughs 
to  mix  the  charge  of  lime  and  water,  are  also  used.  After  hydration 
the  slaked  lime  is  screened  and  ground  to  fine  powder,  and  then  packed 
for  market.  Hydrated  lime  does  not  deteriorate  so  rapidly  in  stor- 
age and  the  fire  risk  is  greatly  reduced.  It  can  be  mixed  with  cement 
and  other  materials,  where  quicklime  is  not  suitable. 

The  following  are  a  few  of  the  important  uses  of  lime  in  the  arts : 
in  mortar  and  cement  mixing ;  in  bleaching  powder ;  in  the  alkali 
manufacture ;  for  purifying  illuminating  gas ;  in  the  preparation  and 
purification  of  many  chemicals,  such  as  acetic,  citric,  oxalic,  and  tar- 
taric  acids,  caustic  soda  and  potash,  etc. ;  for  purifying  sugar  solutions  ; 
in  bleaching  cotton ;  in  tanning ;  in  glass  making ;  in  metallurgical 
operations;  for  disinfecting,  etc. 

Mortar  is  an  aqueous  pasty  mixture  of  slaked  lime,  sand,  and 
other  materials,  which  dries  without  excessive  shrinkage  and  be- 
comes hard  on  exposure  to  the  air,  owing  to  absorption  of  carbon 
dioxide  and  formation  of  carbonate  of  lime.  It  will  not  harden 
while  it  remains  very  wet,  and  this  is  one  of  the  chief  differences  be- 
tween mortar  and  cement.  The  hardening  of  the  two  substances  is 
due,  in  part  at  least,  to  different  causes. 

If  a  paste  of  freshly  slaked  lime  is  allowed  to  dry  by  exposure  to 
the  air,  it  shrinks  considerably,  and  if  in  thick  masses,  numerous 
cracks  are  formed.  The  admixture  of  three  or  four  volumes  of  sharp 
sand  prevents  this  shrinkage  by  separating  the  lime  paste  into  very 
thin  layers,  which  fill  the  spaces  between  the  grains  of  sand.  The 
sand  also  gives  the  mortar  a  porous  structure,  which  facilitates  the 
penetration  of  the  carbon  dioxide  during  the  hardening  period.  The 
interlacing  crystals  of  calcium  carbonate  enclose  the  sand  grains  and 
join  them  together,  thus  increasing  the  hardness  and  strength  of  the 
mortar.  This  addition  of  sand  also  cheapens  the  mortar  by  increas- 
ing the  mass  obtained  from  a  given  amount  of  lime.  "  Fat  lime  " 
requires  a  much  larger  proportion,  which  is  replaced  in  part  by  the 
impurities  in  "  poor  "  lime. 

For  a  good  mortar  it  is  necessary  that  the  lime  be  thoroughly 
slaked,  in  the  proper  quantity  of  water  added  all  at  once,  or  the 
product  is  apt  to  be  granular  and  lumpy.  The  mass  is  covered  with 


180  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

a  layer  of  sand,  or  with  boards  or  canvas,  to  retain  the  heat  and 
moisture,  and  is  not  stirred  w.hile  slaking,  but  is  allowed  to  swell  and 
fall  to  powder  without  disturbance.  Water  is  then  added,  and  the 
paste  allowed  to  stand  for  several  days,  or  even  weeks,  well  protected 
from  the  air,  before  being  stirred  up  with  more  water  for  use  in  mortar. 

The  first  change  noticeable  in  a  mortar  is  the  "  set,"  which  is  a 
solidification  of  the  mass,  due  to  the  loss  of  its  water  through  evapo- 
ration or  absorption  by  the  bricks,  etc.  But  it  is  not  until  the  mass 
becomes  nearly  dry  that  the  real  hardening  begins.  This  is  very  slow, 
since  it  progresses  from  without  towards  the  interior  of  the  mass ; 
and  the  surface  layer  of  calcium  carbonate  first  formed  is  but  slowly 
penetrated  by  carbon  dioxide  from  the  air.  The  interior  of  thick 
walls  will  often  show  an  alkaline  reaction  after  the  lapse  of  a  century 
or  two,  but  after  twenty-five  years  the  change  is  very  slight  under 
ordinary  conditions.  After  several  hundred  years  there  appears  to 
be  a  certain  amount  of  combination  between  the  silica  of  the  sand 
and  the  calcium  carbonate  to  form  a  hydrated  silicate  of  calcium. 
This  secondary  reaction  does  not  increase  the  hardness  of  the  mor- 
tar. Hardening  is  a  true  chemical  change,  and  should  not  be  too 
rapid  for  the  best  results.  In  order  to  hasten  the  hardening  of 
mortar  and  plastering  in  new  houses,  builders  sometimes  build  coke 
or  charcoal  fires  in  open  grates  or  baskets.  But  this  is  liable  to 
cause  uneven  drying  and  excessive  shrinkage,  resulting  in  cracks  or 
scaled  places.  In  certain  mortars  hair  or  other  fibrous  material  is 
added  to  increase  the  toughness,  especially  while  wet. 

Since  mortar  does  not  harden  until  dry,  it  should  never  be  used 
in  damp  places,  such  as  foundations  and  cellars,  nor  in  very  thick 
walls.  Sometimes  it  is  mixed  with  some  cement,  increasing  its 
strength  and  usefulness.  When  thoroughly  hardened,  good  mortar 
is  about  as  hard  as  limestone,  and  adheres  firmly  to  the  bricks  or 
stones  of  the  wall. 

Sand-lime  bricks  *  made  by  mixing  sand  with  about  8  per  cent  of 
slaked  lime,  moulding  the  mixture  in  a  brick  mould  and  subjecting 
the  product  to  the  action  of  steam  at  pressures  of  130  to  150  Ibs.  per 
square  inch,  for  four  or  five  hours,  have  come  into  general  use  for 
building  purposes,  especially  for  inside  work.  It  is  claimed  that 
under  the  action  of  the  steam  at  high  pressure,  the  lime  and  sand  com- 
bine to  form  calcium  silicates,  possibly  similar  to  Portland  cement. 
But  this  seems  doubtful,  as  the  temperature  is  not  comparable  with 

*  Trans.  Am.  Ceramic  Soc.,  1903  ;  1911,  648.  Jour.  Soc.  Chem.  Ind.,  1899,  48 ; 
1902,  1183;  1903,  421. 


LIME,   CEMENT,  AND  PLASTER  OF  PARIS  181 

that  required  for  cement  making.  Possibly  the  bonding  substance 
is  a  mixture  of  the  three  calcium  silicates,  but  chiefly  the  meta-sili- 
cate  (CaSiO3  •  H2O). 

CEMENT 

Cement  consists  of  certain  anhydrous  double  silicates  of  calcium 
and  aluminum,  which  are  capable  of  combining  chemically  with 
water,  to  form  a  hard  mass.  It  differs  from  lime  mortar  in  that  it 
hardens  while  wet,  does  not  require  the  presence  of  carbon  dioxide 
for  hardening,  and  is  very  insoluble  in  water.  It  is  well  adapted  for 
use  in  moist  places,  or  even  under  water,  and  since  its  hardening  is 
simultaneous  throughout  the  whole  mass,  and  is  quite  rapid  in  most 
varieties,  it  finds  extensive  use  in  building  operations. 

There  are  three  general  classes  of  cement :  — 

1.  Those  formed  from  certain  volcanic  tufas,  or  from  artificial 
mixtures  resembling  these.     Such  cements  generally  need  the  addi- 
tion of  lime  before  they  display  hydraulic  properties,  i.e.  form  in- 
soluble silicates  when  treated  with  water.     In  this  group  are  the 
natural  volcanic  tufas,  Pozzuolan,  trass,  and  Santorin  earth,  together 
with  blast  furnace  slags  and  certain  coal  ashes,  which  are  occasion- 
ally used. 

2.  Those  which  contain  a  large  proportion  of  free  lime,  having 
been  made  by  burning  natural  argillaceous  limestones  at  a  tempera- 
ture sufficiently  high  to  drive  off  all  the  carbon  dioxide,  but  not  to 
fuse  the  product.     These  include  "  hydraulic  limes  "   (p.  178)  and 
Roman  cements. 

3.  Those  prepared  by  burning  an  intimate  mixture  of  clay  or 
other  alumino-siliceous  material  and  powdered  calcium  carbonate, 
at  a  very  high  temperature,  so  that  incipient  fusion  takes  place  in 
the  mass.     These  constitute  the  Portland  cements. 

Pozzuolanic  cements  are  chiefly  derived  from  volcanic  tufas, 
found  in  Italy,  near  Naples  (Pozzuoli),  in  the  islands  of  the  Grecian 
archipelago,  and  in  Germany  near  Andernach  on  the  Rhine.  These 
tufas  consisting  of  easily  decomposable  silicates  have  resulted  from 
the  action  of  volcanic  fires,  and  need  no  further  treatment  than  fine 
grinding  and  mixing  with  lime.  Such  cements  are  slow  in  hardening, 
but  have  considerable  ultimate  strength.  Pozzuolan  has  been  used 
since  the  time  of  the  Romans,  who  were  well  acquainted  with  its  prop- 
erties. 

Blast  furnace  slag,  high  in  alumina  and  silica,  is  now  much  used 
for  Portland  cement,  limestone  being  the  other  ingredient.  The 


182  OUTLINES   OF   INDUSTRIAL    CHEMISTRY 

melted  slag  is  chilled  and  granulated  by  running  into  water  and  the 
sandy  material  is  dried,  ground  fine,  and  mixed  with  the  ground  lime- 
stone. The  dry  mixture  is  then  calcined  to  produce  a  clinker,  which, 
after  fine  grinding,  yields  an  excellent  cement ;  but  it  may  be  rather 
high  (3  to  4  per  cent)  in  calcium  sulphide. 

Hydraulic  limes  have  already  been  mentioned  (p.  178).  The  free 
lime  which  they  contain  is  sometimes  slaked  with  just  sufficient  water 
to  hydrate'  the  quicklime  before  the  material  is  sold ;  but  not  enough 
water  should  be  added  to  set  the  cement. 

Roman  cement  is  made  by  burning  argillaceous  limestone  in  kilns. 
It  was  first  made  in  England  by  J.  Parker,  who  patented  a  process 
for  preparing  it  from  the  septaria  nodules,  consisting  of  clay  and 
chalk  found  in  the  bed  and  along  the  banks  of  the  Thames  River. 
Later,  the  beds  of  clay  limestones  were  used,  but  as  there  was  much 
irregularity  in  the  composition  of  these  rocks,  the  product  did  not 
give  satisfaction.  But  by  careful  selection  of  the  material  and 
proper  mixing  of  different  kinds  of  stone,  the  quality  of  cement  pro- 
duced has  been  improved.  These  rocks  are  also  found  in  France, 
Holland,  and  Germany,  and  in  the  United  States.  There  are  sev- 
eral deposits  that  are  very  pure  and  vary  but  little  in  the  different 
parts  of  the  bed.  Nearly  all  these  rocks  contain  a  large  percentage 
of  magnesia,  but  this  does  not  appear  to  injure  the  cement  made 
from  them.  Roman  cement  was  first  made  in  this  country  in  New 
York  state,  from  a  rock  found  on  the  banks  of  Rondout  Creek  and 
near  the  Hudson  River,  and  is  called  "  Rosendale,"  from  the  chief 
town  in  the  district ;  it  still  constitutes  a  large  part  of  the  natural 
cement  made  in  this  country.  Another  important  region  is  on  the 
Ohio  River,  near  Louisville,  the  cements  made  there  being  known  by 
the  latter  name.  Pennsylvania,  Illinois,  Wisconsin,  and  Colorado 
also  supply  natural  cement. 

The  rock  is  broken  into  lumps  about  the  size  of  a  goose  egg,  in 
order  to  secure  evenness  in  burning.  The  burning  is  done  in  con- 
tinuous kilns,  as  a  rule,  and  the  temperature  must  be  carefully  regu- 
lated, high  enough  to  drive  out  the  carbon  dioxide,  but  not  to  fuse 
the  rock.  Then  the  rock  is  carefully  ground  and  sifted.  The  finer 
the  grinding,  the  better  the  product.  In  order  to  secure  supposed 
uniformity  in  the  product,  it  is  often  customary  to  mix  rock  from 
several  beds,  in  the  same  kiln,  but  this  is  of  doubtful  benefit. 

The  color  of  Roman  cement  varies  greatly,  from  pale  yellow  to  red- 
brown,  and  is  due  chiefly  to  the  amount  of  iron  and  manganese  oxides 
present.  But  there  should  not  be  great  variations  in  the  color  of  the 


LIME,   CEMENT,   AND  PLASTER  OF  PARIS 


183 


products  made  from  the  same  rock,  as  this  indicates  inequality  in 
burning. 

Roman  cement  is  generally  quick-setting,  and  hence  is  preferred 
by  many  engineers  for  work  under  water.  It  weighs  from  50  to 
56  pounds  per  cubic  foot.  Its  strength  is  inferior  to  Portland  cement. 

The  following  analyses  *  are  of  typical  cement  rock :  — 


N.  Y.,  ULSTEK 
COUNTY, 

ROSE  ND  ALE 

ILLINOIS, 
UTICA 

WISCONSIN, 
MILWAUKEE 

PENNSYLVANIA, 

COPLAY 

CaCO3      
MgCO3                   .     . 

45.91 
26.14 
15.37 

1  11.38 
|    1.20 

42.25 
31.98 
21.12 

|    1.12 

\    1.07 
/    2.46 

45.54 
32.46 
17.56 
\  3.03 
J   1.41 

67.14 
2.90 
18.34 

7.49 
0.19 
3.94 

SiO2     

Fe?*}* 

AL>o3 

Na^O             .... 

K2O 

H2O                    .     .     . 

Undetermined  .     .     . 

Analyses  of  natural  cements :  — 


ROSENDALE 

UTICA 

LOUISVILLE, 
KY. 

LEHIGH 
VALLEY 

SiO-2 

22.75 

35.43 

21.10 

18.28 

A12O3  

1  16.70 

1      7K1 

\    7.43 

Fe2O3  
CaO 

3670 

|    9.92 
33.67 

>    7.51 
44.40 

51.53 

MgO    

16.65 

20.98 

7.00 

2.07 

K2O 

\    «0* 

Na2O                  .     .     . 



_ 

|    0.80 

|    1.50 

CO2      

5.00 



11.18 

16.20 

CaSO4 

. 

6.85 

H2O                    . 

1.30 



1.16 

. 

Undetermined  .<    .     . 

— 

2.93 

Portland  cement  is  entirely  an  artificial  product,  but  represents 
the  most  important  branch  of  the  cement  industry.  The  first  patent 
was  taken  out  in  England,  in  1824,  but  the  process  extended  in  a 
few  years  to  France  and  Germany.  In  the  United  States  the  manu- 
facture of  this  cement  was  begun  in  1878,  at  Coplay,  Penn.,  and 
the  industry  has  become  enormous. 

The  materials  used  are  calcium  carbonate  and  clay  rich  in  silica. 
Limestone  and  shale,  or  marl  and  clay,  are  used  in  this  country  and 


*  W.  A.  Smith,  Mineral  Industry,  Vol.  I,  1892. 


184 


OUTLINES   OF   INPUSTRIAL   CHEMISTRY 


Europe,  and  chalk  and  clay  mud  from  the  estuaries  of  the  Thames 
and  Medway  rivers  are  preferred  in  England.  But  in  any  case  the 
proportion  of  calcium  carbonate  to  aluminum  silicate  must  be  con- 
trolled between  tolerably  narrow  limits. 

The  average  composition  of  raw  materials  is  shown  in  the  follow- 
ing table :  — 


CLAY 

MARL 

LIMESTONE 

SHALE 

SiO2     .     
AUO3                       .     . 

42.20 
1230 

0.50 
020 

3.0 
\ 

15 

Fe2O3  

4.60 

0.10 

1     L5 

7 

CaCO3 

2390 

9450 

960 

71 

MgCO3     

16.05 

2.25 

3.0 

4 

Alkalies,  moisture,  etc. 

0.95 

2.45 

A  most  thorough  mixing  of  the  ingredients  is  very  essential. 
This  is  done  in  two  ways :  the  "  dry  process  "  is  used  when  the 
materials  are  hard  (limestone  and  shale) ;  and  the  "  wet  process  " 
for  soft  materials  containing  much  water  (marl,  chalk,  and  clay). 

The  dry  process  is  simple  and  cheap,  but  requires  excessively  fine 
grinding  for  uniformity  of  the  product.  The  proper  proportions 
(by  weight)  of  shale  and  limestone  are  crushed  together,  and  often 
lightly  calcined  to  drive  off  moisture,  and  then  ground  in  the  Griffin 
mill  or  ball-mill  so  that  80  per  cent  passes  through  a  200-mesh  sieve. 
This  powder  is  usually  fed  directly  to  the  rotary  kiln,  or  may  be 
pressed  into  bricks  and  burned  in  a  shaft  kiln  or  ring  furnace. 

The  wet  process  is  carried  out  in  various  ways,  according  to  the  eco- 
nomic conditions  prevailing  in  each  locality.  Usually  the  clay  and 
chalk  or  marl  are  ground  in  edge-runners  with  heavy  rolls,  and  water 
is  added  till  enough  is  present  (40  to  50  per  cent)  to  make  a  slime  or 
"  slurry  "  which  will  flow  or  can  be  pumped.  Sometimes  a  wash-mill, 
consisting  of  flat  stones  sliding  over  a  smooth  bed  of  stones  or  iron, 
propelled  by  a  rotary  shaft  with  arms,  is  used  for  this  preliminary 
mixing  and  grinding ;  or  a  disintegrator  mill  may  be  employed. 

The  wet  slurry  is  then  pumped  or  run  to  buhrstones  or  tube-mills  (p. 
188)  and  given  a  very  thorough  grinding.  Often  an  intermediate  mix- 
ing is  given  in  tanks  having  rotary  arms,  or  compressed  air  agitators. 

The  next  treatment  of  the  slurry  varies  in  different  mills ;  it  may  be 
settled  or  filtered  and  the  excess  water  run  away ;  the  mud  may  then 
be  pressed  in  a  brick  machine,  or  dried  on  floors  heated  by  waste  heat 
from  the  kilns.  The  bricks  or  lumps  are  then  sent  to  the  kilns.  In 


LIME,   CEMENT,   AND   PLASTER  OF  PARIS 


185 


this  country  the  slurry  is  generally  run  directly  into  the  rotary  kilns, 
the  water  evaporating  in  the  upper  third  of  the  kiln,  and  the  dried 
mass  forming  little  balls  or  gravel-like  lumps,  which  are  thoroughly 
burned  while  passing  through  the  rest  of  the  kiln. 

Various  kinds  of  kilns  are  used  for  Portland  cement  burning,  the  old 
periodic  dome-shaped  or  shaft  kilns  being  still  in  use  in  some  places, 
although  costly  as  to  fuel  and  output.  Continuous  shaft  kilns  are 
more  common,  especially  where  labor  is  cheap  and  fuel  high ;  in 
America  they  have  been  displaced  by  the  rotary  kilns,  which  have 
much  greater  capacity.  In  shaft  kilns,  owing  to  the  high  temperature, 
the  charge  tends  to  stick  to  the  furnace  walls,  unless  careful  attention 
is  given  during  the  burning.  With  rotary  kilns,  the  amount  of  pow- 
dered coal  consumed  varies  from  25  to  40  per  cent  of  the  weight  of 
the  cement  produced. 

The  Dietzsch  two-storied  kiln  (Etageofen)  (Fig.  76)  is  much  used 
abroad  for  Portland  cement.  The  charge, 
introduced  at  (A),  fills  the  vertical  shaft 
or  pre-heating  chamber,  and  absorbs  the 
heat  of  the  escaping  combustion  gases 
as  it  descends  into  the  combusion  cham- 
ber (B).  The  fuel,  either  coke  or  coal, 
is  introduced  through  (D),  while  the  ma- 
terial from  (B)  is  raked  down  into  the 
chamber  (C),  mixing  with  the  fuel,  and 
attaining  there  the  highest  temperature 
of  the  calcination.  The  burned  material, 
mixed  with  the  fuel  ash,  is  withdrawn  at 
(E).  Air  enters  at  (E),  and  passing 
through  the  hot  clinker,  arrives  in  (C)  at 
a  very  high  temperature,  where  it  sup- 
ports the  combustion  of  the  fuel.  The 
hot  gases  passing  off  through  (B)  and  (A) 
serve  to  heat  the  charge  before  it  arrives 

in  (C).  These  kilns  now  are  often  worked  with  forced  draught,  and 
produce  about  7  tons  of  clinker  per  ton  of  coal. 

Hoffmann's  ring  furnace  (Fig.  77)  is  also  much  used  in  cement 
burning.  This  consists  of  an  elliptical  gallery  built  around  a  central 
chimney  (A).  The  gallery  is  divided  into  15  or  20  compartments 
(B,  B)  each  having  a  door.(C)  opening  outside,  a  flue  (D)  leading  to 
the  chimney  (A),  and  a  wide  opening  (D)  into  the  next  compartment. 
Each  flue  has  a  damper,  by  which  connection  with  the  chimney  (A) 


FIG.  76. 


186 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


may  be  opened  or  closed.  The  openings  (E)  between  the  compart- 
ments may  be  closed  with  a  sheet-iron  or  heavy  paper  diaphragm,  as 
will  be  explained  below.  If  the  door  of  the  compartment  on  one  side 
of  the  diaphragm  be  opened,  and  the  damper  of  the  flue  (D)  leading 
from  the  compartment  on  the  other  side  of  the  diaphragm  is  also 
opened,  while  all  the  other  doors  and  flues  are  closed,  the  draught  of 
the  chimney  (A)  will  cause  air  to  enter  the  open  door  and  pass  around 
the  entire  gallery,  through  each  compartment  in  succession,  and 
finally  out  through  the  open  flue  (D)  to  the  chimney.  In  the  roof 
over  the  gallery  are  charging  holes  (G),  several  being  in  each  compart- 
ment, through  which  fuel  is  introduced.  The  furnace  is  run  as 
follows  :  Assume  that  there  are  14  compartments,  as  shown.  Twelve 
compartments  contain  cement  bricks,  and  their  doors  and  chimney 

flues  are  closed.  Sup- 
pose that  No.  1  is 
being  emptied,  while 
No.  14  is  being  filled. 
The  paper  diaphragm 
closes  the  opening  be- 
tween No.  13  and  No. 
14,  and  the  flue  (D)  of 
No.  13  is  open  to  the 

chimney.  Compartment  No.  7  is  at  the  height  of  combustion,  while 
Nos.  6,  5,  4,  3,  2  contain  bricks  which  have  been  burned.  In  Nos.  8,  9, 
10, 1 1, 12  are  bricks  to  be  burned.  Cold  air  is  drawn  in  through  the  open 
door  of  No.  1,  and  passing  in  order  through  Nos.  2,  3,  4,  5,  6  becomes 
heated  by  contact  with  the  hot  bricks  in  these  compartments  until, 
after  passing  through  No.  6,  which  is  still  red  hot,  it  arrives  in  No. 
7  at  a  very  high  temperature.  In  No.  7  the  fuel  is  burning  at  a  white 
heat,  and  the  hot  gases  pass  on  through  Nos.  8,  9,  10,  11,  12,  13, 
from  which  they  escape  to  the  chimney.  By  this  passage  of  the  hot 
gases  through  the  compartments,  the  unburned  bricks  are  heated, 
those  in  No.  8  being  nearly  red  hot ;  but  as  no  fuel  has  been  intro- 
duced into  these  chambers,  combustion  and  white  heat  are  confined 
to  No.  7.  When  No.  14  is  filled  with  green  bricks,  its  doors  are 
closed,  and  also  the  chimney  damper  of  No.  13,  while  that  of  No.  14 
is  opened,  and  the  diaphragm  transferred  to  the  opening  between  No. 
14  and  No.  1.  Fuel  is  now  introduced  into  No.  8,  which  becomes  the 
combustion  chamber,  and  the  door  of  No.  2  is  opened.  The  burned 
bricks  in  No.  2,  having  been  cooled  by  the  passage  of  cold  air,  are 
taken  out,  while  No.  1  is  being  refilled.  Thus  the  cycle  of  operations 


LIME,    CEMENT,   AND   PLASTER  OF  PARIS  187 

goes  on,  each  compartment  in  turn  being  charged  with  fuel  and  made 
the  combustion  chamber.  The  temperature  in  that  compartment 
which  has  just  been  filled  is  only  high  enough  to  dry  the  green  bricks. 

This  furnace  is  very  economical  of  fuel,  one  ton  of  soft  coal  burn- 
ing 6j  tons  of  clinker,  but  it  requires  much  labor.  The  bricks  must 
be  accurately  piled  in  order  that  open  channels  may  be  left  beneath 
the  charging  holes  for  the  fuel,  which  is  thus  made  to  burn  in  a  column 
extending  from  the  floor  to  the  top  of  the  furnace.  Usually  one  com- 
partment is  emptied  each  day,  and  the  fire  is  moved  forward. 

Revolving  furnaces  (Fig.  126,  p.  598)  are  largely  used  for  cement 
burning,  and  have  greatly  advanced  the  Portland  cement  industry  in 
America.  These  kilns  incline  about  5°  to  8°,  are  60  to  220  feet  long, 
6  to  8  feet  in  diameter,  and  are  lined  with  fire-brick.  The  fuel  is 
usually  powdered  coal,  blown  in  at  the  lower  end  of  the  furnace  by 
an  air  blast ;  in  rare  cases  oil  or  natural  gas  may  be  used.  The  mix- 
ture of  powdered  materials  (or  slurry,  in  the  wet  mixing  process) 
enters  at  the  upper  end,  and  is  thoroughly  calcined  during  the  two 
or  three  hours'  passage  through  the  furnace  and  sintered  by  the 
heat  into  little  balls  or  gravel-like  lumps.  The  hot  clinker  is  dis- 
charged into  an  elevator  which  carries  it  to  the  iron  coolers,  in  which 
air  conies  in  contact  with  the  mass.  A  little  water  is  sometimes 
sprinkled  into  the  elevator  buckets  to  "  cure  "  the  clinker  and  insure 
rapid  cooling,  which  assists  materially  in  the  grinding. 

The  rotary  kiln  is  cheap  in  its  labor  account  but  even  the  large 
ones  are  wasteful  of  fuel ;  probably  the  lowest  consumption  is  about 
75  Ibs.  of  coal  per  barrel  of  clinker ;  the  Dietzsch  and  Hoffmann  kilns 
use  about  one-third  this  amount  of  fuel,  but  require  much  higher  ex- 
pense for  labor,  which  probably  explains  the  more  general  use  of 
these  types  in  Europe,  where  fuel  is  costly  and  labor  relatively  cheap. 
Much  depends  on  the  calcination  temperature,  which  should  reach 
1400°  to  1600°  C.  (incipient  fusion),  and  there  is  considerable  shrink- 
age ;  well-burned  clinker  is  semi- vitrified,  hard,  and  of  greenish-black 
color. 

The  clinker  is  then  ground  in  various  types  of  mills  (see  below), 
to  such  fineness  that  not  over  7  or  8  per  cent  is  retained  on  a  sieve 
having  100  meshes  to  the  linear  inch.  Only  the  very  fine  dust  is 
considered  of  value  in  cement. 

The  ball-mill  (Fig.  78)  consists  of  a  cast-iron  drum  (D),  contain- 
ing numerous  chilled-iron  or  steel  balls  (B)  of  different  sizes.  The 
clinker  is  powdered  by  the  rubbing  and  pounding  of  the  balls  as  the 
drum  rotates.  The  dust  passes  through  the  perforated  plates  (P) 


188 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


and  falls  on  the  fine  sieves  (S).  The  coarse  particles  retained  by  the 
screens  return  to  the  interior  of  the  drum  through  the  openings 
(C,  C)  for  further  grinding. 


FIG.  /d. 


The  tube-mill  (Fig.  79)  is  a  horizontal  iron  tube  about  20  feet 
long  by  5  feet  in  diameter,  rotated  some  25  times  a  minute  by  the 
gears  (G).  The  tube  is  half  full  of  smooth  quartz  pebbles,  about  the 
size  of  goose  eggs  ;  these  are  retained  in  the  tube  by  a  screen  (S)  at 
the  outlet  end,  through  which  the  ground  cement  passes  and  is  dis- 
charged through  (T).  The  pebbles  are  slowly  ground  up  with  the 
cement  and  a  few  new  ones  are  added  with  the  clinker  at  regular 
intervals.  The  speed  of  rotation  and  the  rate  of  feed  of  material 
through  the  trunnion  by  the  screw  (P)  determine  the  fineness  of  the 


j      ^ 


FIG.  79. 


product.  These  mills  require  considerable  power  and  have  rather 
small  capacity,  but  any  degree  of  fineness  can  be  obtained,  and  the 
repairs  are  very  moderate.  They  work  equally  well  on  dry  or  wet 
materials  and  are  often  used  to  mix  and  grind  slurry. 

The  Hardinge  conical  mill  (Fig.  80)  is  a  modification  of  the  tube- 
mill,  having  somewhat  greater  efficiency. 

The  Griffin  mill  is  a  steel  roll,  weighing  about  400  pounds,  revolv- 


LIME,    CEMENT,   AND   PLASTER  OF  PARIS 


189 


FIG.  80. 


ing  on  a  vertical  shaft  with  a  gyratory  motion,  and  pressing  by  cen- 
trifugal force  against  a  steel  ring.  It  has  great  capacity,  and  will 
grind  so  that  about  90  per  cent  of  the  product 
passes  a  100-mesh  sieve  ;  but  the  repair  account 
is  rather  large. 

The  Fuller-Lehigh  mill  consists  of  a  hori- 
zontal ring  with  a  ground  inner  surface,  against 
which  several  heavy  steel  balls  are  made  to 
revolve  at  a  speed  of  about  160  r.  p.  m.  The  grinding  effect  is  due  to 
the  centrifugal  force  developed  by  the  whirling  balls. 

The  Kent  mill  (Fig.  81)  consists  of  three  rolls  rotating  at  high  speed, 
within   a    movable   circular  ring    or    die, 
against  which  the  crushing  takes   place. 

The  constitution  of  Portland  cement 
has  been  much  studied,  and  various  views 
are  held  as  to  the  proper  proportions  of 
the  ingredients.  Le  Chatelier  states  * 
that  the  ratio  of  the  equivalents  of  lime 
and  magnesia  to  the  silica  and  alumina 
should  not  exceed  a  maximum  equal  to 
three,  while  that  of  the  total  silica,  minus 
the  combined  iron  and  alumina,  should  not  be  less  than  a  minimum 
equal  to  three  ;  thus  :  — 


FIG.  81. 


CaO  +  MgO  ^  CaO  +  MgO 

= 


Si02  +  A1203 


Si02  -  (A1203  +  Fe203)  = 


^ 


According  to  Michaelis,  the  ratio  of  lime  to  the  acid  constituents 
should  fall  between 


CaO 


SiO2  •  A12O3 


>  1.8  and 


CaO 


SiO2  •  A12O3  •  Fe2O3 


<  2.2. 


Newberryf  holds  that  the  proportion  of  lime,  by  weight,  should 
be  to  the  silica  and  alumina  as  shown  thus :  — 

Lime  =  (SiO2  X  2.8)  +  (A12O3  X  1.1). 

The  composition  of  good  commercial  cements,  however,  shows 
some  variation,  and  no  definite  formula  can  be  assigned  to  them. 
The  following  are  typical :  — 

*  Trans.  Am.  Institute  Mining  Engineers,  22  (1893),  15. 
t  J.  Soc.  Chem.  Ind.,  1897,  887. 


190 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


SiO2 21.05*  22.80*  19.78*   21.50f   22.04f   21.25f 


A1203 


8.95       6.49       8.21       6.60       6.45       6.16 


Fe2O3 4.40  4.31 

CaO 61.30  61.10 

MgO 1.37  .47 

SO3 1.28  1.39 

Alkalies 68  .30 

H,O,  CO2 70  2.40 


4.53 

62.69 

2.09 

1.28 


2.60 

62.50 

1.20 

.98 


3.41  3.85 

60.92  62.69 

3.53  3.00 

2.25  1.50 


1.10        —          — 


0.50 


99.73     99.26     99.68     95.38     98.60     98.95 

The  cause  of  hardening  of  cement  has  been  explained  in  various 
ways.  Le  Chatelier  J  holds  that  during  the  burning  a  tricalcium  sili- 
cate (Ca3SiOs)  is  formed  by  reaction  between  the  clay  and  the  lime, 
and  at  the  same  time,  some  calcium  aluminate  and  ferrite  are  formed, 
besides  mono-  and  di-calcium  silicates.  By  the  action  of  water  on 
the  tricalcium  silicate,  hydrated  monocalcium  silicate  and  calcium 
hydroxide  are  formed :  — 

1)  2  Ca3SiO5  +  9  H2O  =  (CaSiO3)2  5  H2O  +  4  Ca(OH)2. 

Then  the  calcium  hydroxide,  water,  and  calcium  aluminate  may  react 
to  form  hydrated  basic  calcium  aluminate :  — 

2)  Ca3Al2O6  +  Ca(OH)2  +  11  H2O  =  Ca4Al2O7  •  12  H2O. 

The  formation  of  the  hydrated  basic  aluminate  [(CaO)4  •  A12O3  •  12  H2O] 
is  supposed  to  influence  the  setting  of  the  cement,  but  the  hardening 
is  ascribed  to  the  first  reaction.  Richardson  §  takes  the  view  that 
Portland  cement  clinker  is  largely  composed  of  alit,  a  solid  solution 
of  tricalcic  silicate  in  tricalcic  aluminate;  and  that  the  setting  is 
due  to  the  decomposition  of  alit,  with  formation  of  crystals  of  cal- 
cium hydroxide.  Hydration  of  the  silicates  and  alumina tes  is  not 
thought  to  add  to  the  strength  of  the  cement  after  setting,  but  the 
crystallization  of  the  calcium  hydroxide  binds  the  mass  together. 

Portland  cement  is  usually  slower  in  setting  than  Roman,  but 
when  the  hardening  has  begun,  it  progresses  more  rapidly  with  the 
former.  There  is  very  little  increase  of  hardness  after  six  months. 
Portland  cement  is  more  durable  than  Roman  under  most  conditions, 
and  is  generally  stronger.  It  forms  a  denser  and  heavier  powder  of 
a  greenish  gray  color,  but  when  hardened  has  a  drab  shade  resembling 
the  color  of  the  stone  quarried  at  Portland,  England,  and  used  much 
for  building  in  that  country ;  hence  the  name.  Variations  in  color 


*  English.  f  American. 

J  Annales  des  Mines,  1887,  388.     J.  Soc.  Chem.  Ind.,  1888,  567,  847. 
dustrie  Zeitung,  16  (1892),  1032.     Chemiker  Zeitung,  1892,  Ref.  342. 
§  Proc.  Assoc.  Port.  Cement  Mfgr.,  1905,  June  15. 


Thonin- 


LIME,    CEMENT,   AND   PLASTER  OF  PARIS  191 

of  the  same  brand  of  cement  may  show  changes  in  quality ;  if  under- 
burned,  it  is  generally  yellowish.  The  weight  per  cubic  foot  varies 
from  about  70  to  90  pounds  ;  the  finer  the  grinding,  the  less  the  weight. 
But  as  a  rule  heavy  cements  are  preferred  by  builders,  as  they  are  sup- 
posed to  be  more  thoroughly  burned ;  they  are,  however,  slow  in  setting. 

The  testing  of  cement  is  generally  the  work  of  the  engineer.  Chemical 
analysis  alone  is  of  small  use  in  determining  its  properties,  and  physical 
tests  are  usually  more  satisfactory.  Committees  from  the  American 
Society  for  Testing  Materials,*  and  from  the  American  Society  of  Civil 
Engineers,!  and  other  engineering  associations  have  adopted  "  Standard 
Specifications  "  and  "  Methods  of  Testing."  The  tests  recommended, 
are  for :  — 

(a)  Specific  Gravity.         (6)  Fineness.         (c)  Time  of  Setting. 
(d)  Tensile  Strength.  (e)  Soundness. 

The  specific  gravity  of  the  cement  dried  at  100°  C.  shall  not  be  less 
than  3.10.  The  determination  is  made  in  Le  Chatelier's  apparatus, 
using  naphtha  of  62°  Be.,  or  kerosene. 

In  testing  for  fineness,  not  more  than  8  per  cent  by  weight  may 
remain  on  the  No.  100,  nor  more  than  25  per  cent  on  the  No.  200  sieve. 
Use  circular  sieves,  20  centimeters  in  diameter,  with  woven  cloth  of 
brass  wire  0.0045  inch  and  0.0024  inch  in  diameter  respectively,  for 
the  sieves.  Fifty  or  100  grams  cement,  dried  at  100°  C.,  are  to  be  used 
for  the  test. 

Time  of  Setting.  —  The  cement  shall  develop  the  initial  set  in  not 
less  than  30  minutes,  and  should  set  hard  in  not  less  than  one  hour  nor 
more  than  10  hours.  The  test  is  to  be  made  with  the  Vicat  needle, 
which  is  a  movable  vertical  rod,  with  a  plate  on  the  upper  end  and  a 
short  cylinder,  1  millimeter  in  diameter,  at  the  bottom,  the  whole  sup- 
ported in  a  frame.  The  rod,  plate,  and  foot-piece  weigh  300  grams. 
A  paste  of  cement  and  water  is  put  into  a  frame  under  the  needle  point, 
and  the  depth  to  which  the  needle  sinks  in  the  soft  mass  is  noted.  The 
set  has  commenced  when  the  needle  ceases  to  penetrate  to  within  5 
millimeters  of  the  glass  plate  on  which  the  paste  rests,  and  is  terminated 
when  the  needle  no  longer  enters  the  mass. 

Time  of  setting  determinations  are  not  exact,  and  vary  with  the 
quantity  of  water  used  in  the  mortar,  the  temperature  of  the  water 
and  of  the  air,  and  the  amount  of  working  the  mortar  may  have  re- 
ceived during  the  moulding  for  the  tests.  If  the  set  begins  in  less  than 
half  an  hour,  the  cement  is  called  "  quick-setting,"  and  is  desirable  for 
work  under  water.  Slow-setting  cement  requires  more  than  half  an 
hour  for  the  set  to  begin;  this  is  better  for  most  purposes  and  may  be 
mixed  in  larger  quantities.  High  temperatures  hasten  the  set  of  the 
cement,  while  a  larger  proportion  of  water  induces  slower  setting.  The 

*  Proc.  Am.  Soc.  Testing  Materials,  1904. 

t  Trans.  Am.  Soc.  Civil  Engineers,  1903 ;    amended  1904. 


192 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


addition  of  not  more  than  2  per  cent  of  calcium  sulphate,  as  gypsum  or 
plaster  of  Paris,  retards  the  set  materially.  Larger  quantities  may  hasten 
the  set. 

For  ordinary  control  work,  the  time  of  setting  may  be  determined 
sufficiently  closely  by  the  "  normal  needle,"  devised  by  Gilmore.  Two 
of  these  are  used :  one  is  a  wire  one-twelfth  of  an  inch  in  diameter  and 
loaded  with  a  weight  of  one-quarter  of  a  pound ;  the  other  wire  has  a 
diameter  of  one  twenty-fourth  of  an  inch  and  carries  a  weight  of  one 
pound.  The  cement,  mixed  to  a  stiff  paste  with  water,  is  formed  into  a 
pat,  one-half  an  inch  thick,  and  the  time  noted  until  no  impression  is 
made  upon  it  by  the  point  of  the  first  wire.  This  is  the  beginning  of  the 
'*  set."  When  the  second  wire  will  not  penetrate,  the  set  is  ended. 

The  tensile  strength  is  determined  on  a  briquette,  shaped  like  an 
hour-glass,  and  having  at  the  narrow  portion  a  section  exactly  one  inch 
square.  The  minimum  requirements  shall  be  within  the  following 
limits :  — 


AGE 

STRENGTH 

For    "neat  "    cement 
(i.e.  without  sand) 

Sand  briquettes  (1  part 
cement,  3  parts  sand) 

24  hours  in  moist  air 
7  da.  (  1  da.  in  moist  air  ;     6  da.  in 
water) 
28  da.  (1  da.  in  moist  air  ;  27  da.  in 
water) 
7  da.  (1  da.  in  moist  air  ;    6  da.  in 
water) 
28  da.  (1  da.  in  moist  air  ;  27  da.  in 
water) 

150-200  Ib. 
450-550  Ib. 
550-650  Ib. 
150-200  Ib. 
200-300  Ib. 

For  the  sand  briquette,  a  natural  sand,  obtainable  at  Ottawa,  Illinois, 
is  recommended,  but  many  engineers  prefer  a  standard  sand  made  by 
pulverizing  pure  quartz.  The  sand  is  sifted  and  that  portion  used  which 
passes  a  No.  20  sieve  and  is  retained  by  a  No.  30.  The  briquettes  must 
be  carefully  made  to  secure  uniform  results.  The  cement  is  mixed  with 
water  at  about  70°  F.,  filled  into  bronze  moulds,  pressed  down  well,  and 
smoothed  off  evenly.  This  is  done  on  a  slate  or  glass  plate  to  prevent 
absorption  of  moisture.  When  set,  the  briquette  is  removed  and  placed 
in  a  moist-air  closet  for  24  hours.  It  is  then  kept  in  water  until  the  test 
is  made,  when  it  is  placed  in  the  jaws  of  a  machine,  which  applies  a  gradu- 
ally increasing  tension  at  the  rate  of  400  pounds  per  minute.  The  num- 
ber of  pounds  necessary  to  fracture  the  briquette  is  read  on  a  graduated 
scale  beam.  The  average  of  three  tests  (of  each  neat  and  sand-mixture) 
is  usually  taken  as  the  tensile  strength. 

The  less  water  used  in  the  cement  mortar,  the  higher  the  strength, 
as  a  rule,  especially  in  the  short  time  tests.  For  neat  cement,  the  water 
may  vary  from  14  to  24  per  cent ;  for  sand  briquettes,  about  12  per  cent 
of  the  total  weight  of  the  sand  and  cement.  The  cement  and  sand  should 
be  well  mixed,  dry;  then  wet  out,  and  mixed  with  water  in  about  2^ 
minutes,  and  filled  into  the  moulds  at  once. 


LIME,    CEMENT,   AND   PLASTER  OF  PARIS  193 

Compression  tests  are  made  with  small  cubes  of  the  cement.  This 
test  should  show  at  least  ten  times  the  tension  resistance.  This  being 
difficult  to  manage,  the  tensile  test  is  employed  instead  usually. 

Soundness  tests  are  made  upon  pats  of  neat  cement,  3  inches  in 
diameter,  one-half  inch  thick  at  the  centre  and  tapering  to  a  thin  edge. 
These  are  kept  in  moist  air  for  24  hours ;  then  one  is  exposed  to  air  at 
ordinary  temperature  for  28  days ;  another  is  kept  in  water  at  70°  F.  for 
28  days;  a  third  is  exposed  to  steam  in  a  loosely  covered  vessel  for  5 
hours.  All  of  the  pats  must  show  no  signs  of  checking,  cracking,  dis- 
integrating, nor  distortion.  Faija's  test  is  often  used.  This  consists 
in  placing  the  test  piece  in  a  moist  atmosphere  at  100°  to  105°  F.,  for  6 
hours  or  more,  till  well  set ;  then  it  is  immersed  in  water  at  115°  to  120°  F. 
for  the  remainder  of  24  hours. 

Expansion  or  "  blowing  "  is  shown  by  swelling,  cracking,  or  disin- 
tegration of  the  cement  after  setting.  This  is  generally  supposed  to 
be  caused  by  excess  of  free  lime,  or  by  poor  burning,  the  heat  not  having 
been  enough  to  combine  the  lime  with  the  silica  and  alumina.  The  free 
lime  slakes  after  the  cement  has  set,  and  the  expansion  causes  disin- 
tegration. Magnesia  in  Portland  cement  has  been  thought  to  cause 
unsoundness,  but  up  to  4  per  cent  (as  MgO)  appears  to  be  harmless,  and 
is  allowed  by  the  Standard  specifications.  . 


PLASTER  OF  PARIS 

Plaster  of  Paris  is  made  by  heating  gypsum  (CaSO4  •  2  H2O)  until 
about  three-fourths  of  its  water  of  crystallization  is  driven  off.  The 
process,  called  burning,  is  carried  on  in  muffle  furnaces,  kettles,  or 
rotary  cylinders.  Direct  contact  with  the  fuel  is  avoided,  lest  the 
carbonaceous  matter  may  reduce  some  of  the  calcium  sulphate  to 
sulphide ;  nor  should  the  flame  come  in  contact  with  the  gypsum, 
but  only  the  hot  gases.  Boiler-iron  kettles,  having  a  stirring  device, 
are  much  used,  the  charge  being  5  to  7  tons  of  finely  ground  gypsum, 
which  requires  about  three  hours  to  calcine.  Rotary  calciners  are 
being  adopted  because  of  their  economy ;  these  are  iron  cylinders  set 
at  a  slight  incline,  and  heated  externally  by  the  flame  from  a  furnace. 
Gypsum,  crushed  to  small  size,  is  fed  continuously  into  the  cylinder ; 
the  calcined  material  is  friable  and  easily  ground  fine. 

Gypsum  contains  about  21  per  cent  of  water  of  crystallization, 
while  plaster  retains  4  to  7  per  cent.  Moisture  begins  to  escape  at 
about  100°  C.,  but  the  most  favorable  temperature  for  calcining  is 
around  145°  C. ;  if  heated  to  200°  C.,  all  the  crystal  water  is  expelled, 
and  the  product  will  combine  with  water  very  slowly,  the  property 
of  rapid  setting  being  lost.  Thus  the  limits  of  heating  are  very 
narrow  and  much  care  is  needed  in  the  process, 
o 


194  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

When  mixed  with  water,  plaster  of  Paris  forms  a  paste  which 
soon  hardens  or  "  sets,"  owing  to  a  recombination  of  water  with  the 
burned  plaster,  to  form  hydrated  calcium  sulphate.  The  theory  of 
this  setting  has  been  explained  by  Le  Chatelier.*  The  composition 
of  the  plaster  is  essentially  (CaSO^  •  H2O,  a  salt  which  is  soluble, 
and  part  of  which  dissolves  in  the  water  used  in  mixing.  But  as 
soon  as  it  dissolves,  a  combination  between  it  and  some  of  the  water 
takes  place,  forming  CaSO4  •  2  I^O ;  this,  being  much  less  soluble 
than  the  monohydrated  salt,  at  once  begins  to  crystallize  from  the 
solution,  forming  a  network  of  crystals.  Then  more  of  the  plaster 
dissolves,  becomes  fully  hydrated,  and  crystallizes  out,  increasing 
the  solidity  of  the  "  set  "  by  the  interlacing  of  new  crystals  with 
those  already  formed.  Thus  the  cycle  of  reactions  goes  on  until  the 
plaster  is  fully  hydrated. 

The  theoretical  quantity  of  water  necessary  to  set  plaster  is  about 
18  per  cent  of  its  weight ;  but  in  fact,  from  30  to  35  per  cent  is  generally 
used.  Excess  of  water  renders  the  mass  more  plastic  and  retards  the 
setting.  Large  excess  causes  disintegration  of  the  plaster,  if  left  in 
contact  with  it  for  some  time  after  setting,  owing  to  the  solution  of 
some  of  the  crystallized  calcium  sulphate.  Since  plaster  "  sets  " 
very  rapidly  with  water,  a  "  retarder,"  such  as  glue,  dried  blood,  or 
vegetable  gums,  marshmallow  root,  or  fine  sawdust,  is  often  added. 
These  colloidal  bodies  probably  decrease  the  solubility  of  the  calcined 
plaster  and  retard  the  hardening  for  half  an  hour  or  more. 

Plaster  expands  slightly  while  setting,  and  hence  is  valuable  for 
making  casts  and  reproductions.  It  is  used  for  interior  decorative 
work  and  also  as  a  cement  for  joining  glass  and  metal  ware.  The 
surface  of  plaster  after  setting  is  rather  soft,  and  if  it  is  desired  to 
increase  the  hardness,  this  may  be  done  by  mixing  alum,  borax,  or 
tartaric  acid  with  it,  or  by  adding  some  alcohol  to  the  water  with 
which  the  plaster  is  mixed.  However,  these  substances  retard  the 
setting.  By  painting  or  dipping  plaster  casts  in  melted  wax,  paraffine 
or  stearin,  or  in  solutions  of  these  in  petroleum  ether,  the  pores  are 
filled  and  the  surface  is  made  smooth,  so  that  dirt  will  not  adhere 
and  the  articles  may  be  washed.  When  treated  with  a  solution  of 
barium  hydroxide,  the  surface  of  the  plaster  is  coated  with  barium 
sulphate  and  rendered  insoluble.  If  plaster  is  mixed  with  a  solution 
of  glue  or  size,  the  material  called  "  stucco  "  is  obtained. 

*  Comptea  Bendus,  Vol.  96,  717,  1668. 


LIME,    CEMENT,   AND   PLASTER   OF  PARIS  195 


REFERENCES 

Die  hydraulische  Morter.     Michaelis,  1869. 

A  Practical  Treatise  on  Limes,  Hydraulic  Cement,  and  Mortars.     Q.  A. 

Gilmore,  1874. 

Chemische  Technologic  der  Mortelmaterialien.     G.  Feichtinger,  1885. 
Recherches  experimentales  sur  la  Constitution  des  Mortiers  hydrauliques. 

Le  Chatelier,  Paris,  1887. 
Fabrication  et  Controlle  des  Chaux  hydrauliques  et  des  Ciments.     H. 

Bonnami,  Paris,  1888.     (Gauthier-Villars  et  Fils.) 
Zement  und  Kalk.     Rudolf  Tormin,  Weimar,  1892.     (B.  F.  Voigt.) 
A  Manual  of  Lime  and  Cement.     A.  H.  Heath,  London,  1893.     (Spon.) 
Annales  des  Mines:—  XI  (1887),  388-465.     H.  Le  Chatelier. 
Cements,  Limes  and  Plasters.     Edwin  C.  Eckel,  New  York,  1907. 
The  Modern  Manufacture  of  Portland  Cement.     Percy  C.  H.  West,  1910. 
Portland  Cement.     Richard  K.  Meade,  2d  ed.,  Easton,  Pa.,  1911. 
Journal  of  American  Chemical  Society  :  — 1894,  161.     T.  B.  Stillman. 
Journal  of  the  Society  of  Chemical  Industry :  — 

1886,  188,  199.     1891,  927.     1897,  887.     1910,  1107. 
Trans.  Am.  Inst.  Min.  Eng.,  27,  508.     P.  Wilkinson. 
Transactions  of  the  American  Society  of  Civil  Engineers :  — 

1877.     W.  F.  Maclay.     1885.     E.  C.  Clarke. 

1885,  1903  ;    1904.     Report  of  Committee  on  Cement  Tests. 

1893.     Max  Gary. 


GLASS 

Glass  is  an  amorphous,  transparent,  or  translucent  mixture  of 
silicates,  one  of  which  is  always  that  of  an  alkali.  The  usual  silicates 
employed  are  those  of  potassium,  sodium,  calcium,  and  lead ;  the  sili- 
cates of  heavy  metals  occur  in  the  colored  glasses.  Glass  is  not 
readily  decomposed  by  water  or  acids  (excepting  HF).  Its  behavior 
towards  solvents  generally  tends  to  show  that  it  is  a  mixture  of 
silicates,  rather  than  a  definite  compound. 

Most  simple  silicates  and  mixtures  of  them  are  difficult  to  fuse, 
and  when  cooled  after  fusion,  have  a  crystalline  structure ;  but  the 
alkali-lime  and  alkali-lead  silicates  fuse  easily,  and  are  generally 
amorphous  after  fusion.  Silicic  acid  is  capable  of  forming  a  number 
of  salts  of  varying  acid  content  and  of  approximately  equal  stability. 
Hence  from  a  fusion  of  the  silicates  of  two  or  more  metals,  the  tendency 
of  any  particular  compound  to  crystallize  is  small,  and  even  if  a 
crystal  centre  is  formed,  growth  is  very  slow,  because  of  the  viscosity 
of  the  medium  and  the  major  part  of  the  liquid  consisting  of  dissimilar 
molecular  structures.  Hence  such  a  mass  can  be  supercooled,  the 
viscosity  progressively  increasing,  and  the  melt  becoming  first  plastic 
and  finally  rigid.  Such  a  supercooled  liquid  is  called  a  glass ;  it  has 
no  melting  point,  but  softens  progressively  on  heating,  and  if  kept 
thus  for  some  time  crystallization,  technically  called  "  devitrification," 
will  begin,  causing  a  white  or  porcelain-like  appearance.  The  alkali- 
lime  and  alkali-lead  silicates  are  rigid  at  ordinary  temperatures,  in- 
soluble in  most  liquids,  decrease  in  viscosity  slowly  when  heated,  so 
that  they  are  plastic  and  workable  over  a  large  temperature  range, 
and  devitrify  very  slowly.  These  properties  give  them  their  technical 
importance. 

Since  the  glasses  are  complex,  homogeneous  mixtures,  all  of  their 
properties  can  be  progressively  changed  by  a  progressive  modification 
of  composition,  and  use  of  this  is  made  in  the  arts. 

Soda-lime  glass  approaches  Na2O,  CaO,  6  SiO2,  and  lead  glass, 
IQO,  PbO,  6  SiO2 ;  but  it  may  vary  so  much  that  the  formula  becomes 
5  K2O,  7  PbO,  36  SiO2.  Of  course  potash  may  be  substituted  for  soda, 
or  vice  versa,  in  either  kind,  while  the  relative  proportion  of  the  several 
ingredients  may  vary  between  quite  wide  limits.  But  as  a  rule,  the 
higher  the  percentage  of  silica,  the  harder,  more  difficultly  fusible, 
and  more  brittle  the  glass.  Increase  of  alkali  makes  it  softer,  more 

196 


GLASS  197 

fusible,  and  less  capable  of  resisting  atmospheric  changes  and  chemical 
reagents.  Increasing  the  percentage  of  lime  decreases  the  fusibility 
and  renders  it  harder,  but  not  so  brittle  as  in  the  case  of  high-silica 
content.  If  the  alkali  used  be  mixed  soda  and  potash,  a  more  fusible 
glass  is  obtained  than  from  either  alone.  Part  of  the  lime  or  lead  may 
be  replaced  by  oxides  of  other  metals,  e.g.  of  iron,  manganese,  cobalt, 
copper,  barium,  zinc,  tin,  arsenic,  etc.,  and  this  is  generally  the  case, 
to  some  extent,  in  common  glass,  and  to  a  greater  degree  in  colored 
glass.  Aluminium  oxide  may  replace  some  of  the  silica ;  the  former 
is  often  present  in  considerable  amounts,  and  renders  the  product 
tough.  Certain  fluorides,  e.g.  calcium  fluoride,  also  enter  into  the 
composition  of  some  varieties.  Besides  the  above-named  oxides,  cer- 
tain borates  and  phosphates  are  occasionally  used,  to  replace  a  part 
of  the  silica  in  glass  manufactured  for  various  optical  and  chemical 
purposes  ;  these  usually  contain  zinc  or  barium  also.  The  well-known 
"  optical  glass,"  made  in  Germany,  contains  both  zinc  and  boron. 

Technically,  two  kinds  of  glass  are  recognized :  lime  glass  and 
lead  glass.  The  alkali  used  may  be  soda,  or  potash,  or  both.  Lime 
glass  is  most  common  and  generally  useful.  It  is  cheaper,  harder, 
more  resistive,  and  less  fusible  than  lead  glass ;  the  latter  has  greater 
lustre  and  brilliancy,  is  heavy  and  expensive  and  is  used  chiefly  for 
cut  ware  and  for  optical  purposes. 

The  essential  materials  for  glass  making  are  silica,  an  alkali,  and 
lime  or  lead.  Silica  was  formerly  derived  from  quartz  or  flint ;  but 
this  is  now  only  used  for  a  particularly  fine  quality.  It  is  heated  to 
a  red  heat,  and  dropped  into  water,  and  the  friable  mass  so  formed 
is  powdered  in  a  mill.  Quartz  sand  and  soft  quartzites  are  the  usual 
sources  of  silica,  and  numerous  deposits  are  worked  in  different  coun- 
tries. Sand  of  great  purity  is  found  in  Germany,  near  Aix-la-Chapelle, 
and  at  Nivelstein ;  in  France,  at  Fontainebleau ;  in  Belgium ;  in  Eng- 
land ;  and  in  Australia.  In  the  United  States,  extensive  beds  are 
worked  in  Berkshire  Co.,  Mass.,  and  in  Pennsylvania,  along  the  Juniata 
River.  The  Berkshire  deposit  is  a  soft  white  sandstone,  which,  when 
crushed,  yields  sand  which  is  from  99.6  to  99.8  pure  SiO2.  The  Juniata 
stone  is  slightly  yellow  in  color,  and  the  sand  is  from  98.8  to  99.7  pure 
SiO2.  The  most  troublesome  impurity  in  sand  is  iron ;  for  white  glass, 
there  should  never  be  more  than  0.5  per  cent  Fe2O3. 

Alkali  is  derived  from  the  carbonate  or  sulphate  of  soda  or  potash, 
and  these  also  must  be  free  from  iron.  Carbonate  fuses  more  readily 
with  the  sand  than  does  sulphate,  but  since  the  latter  is  cheaper,  it 
is  much  used.  It  is  essential  to  mix  carbon  in  some  form  with  the 


198  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

sulphate,  to  assist  in  reduction.  For  better  grades  of  glass,  charcoal 
dust  is  used,  but  for  common  glass,  powdered  coal  is  the  reducing 
agent.  The  exact  nature  of  the  reaction  with  sulphate  appears  some- 
what uncertain :  — 

Na2SO4  +  SiO2  +  C  =  Na2SiO3  +  SO2  +  CO.* 

For  lead  glass,  sulphates  are  not  generally  used,  since  some  sodium 
sulphide  is  formed  by  the  reduction  of  the  sulphate,  and  this  reacts 
with  the  lead,  forming  lead  sulphide,  which  darkens  the  glass. 

Attempts  to  use  salt  directly  in  the  glass  furnace,  as  a  source  of 
alkali,  have  not  proved  satisfactory.  It  is  quite  volatile  at  the  tem- 
perature of  the  furnace,  and  the  presence  of  air  or  steam  is  necessary 
for  its  decomposition  by  the  silica. 

For  potash,  crude  pearlash  may  be  used ;  but  in  the  better  grades 
of  glass  the  refined  pearlash  is  employed.  Sulphate  of  potassium  is 
difficult  to  reduce,  and  is  not  much  used. 

Lime  is  derived  from  chalk  or  limestone.  For  very  fine  glass,  pure 
marble  dust,  as  free  as  possible  from  iron,  is  employed.  For  common 
grades,  less  pure  limestone  is  used.  It  may  contain  a  high  percentage 
of  silica  and  considerable  alumina,  but  magnesia  or  iron  in  large 
amounts  is  objectionable.  Magnesia  makes  the  glass  hard  and  infu- 
sible. In  cheap  glass,  limestone  is  sometimes  replaced  in  part  by  fel- 
spar, porphyry,  or  granite.  Carbonates  of  both  alkali  and  lime  are 
advantageous  in  the  glass  mixture,  since,  as  the  mass  fuses,  the  escap- 
ing bubbles  of  carbon  dioxide  serve  to  stir  up  and  mix  the  ingredients 
more  thoroughly. 

Lead  is  added  as  litharge  (PbO),  or  red  lead  (Pb3O4).  The  latter 
is  preferred,  since  the  oxygen  liberated  from  it  is  thought  to  assist  in 
decolorizing  the  glass  by  oxidizing  the  iron ;  it  also  prevents  reduction 
of  metallic  lead.  It  is  essential  that  the  litharge  and  red  lead  be  free 
from  copper  and  silver. 

Besides  the  above  requisites,  it  is  customary  to  employ  other  in- 
gredients in  every  glass  mixture,  to  assist  in  the  decolorization  or 
fusion.  The  commonest  decolorizing  material  added  is  pyrolusite 
(binoxide  of  manganese,  MnO2).  Iron,  when  in  the  ferrous  condition, 
imparts  a  green  color  to  glass ;  but  when  in  the  ferric  state,  it  is  much 
less  troublesome,  since  it  only  gives  a  pale  yellow  color.  By  the 
oxidizing  action  of  the  pyrolusite,  ferrous  iron  is  converted  to  the 
ferric  condition ;  moreover,  the  silicate  of  manganese  has  a  violet  or 
pink  color,  and  so  helps  to  neutralize  the  green.  Only  a  very  small 

*  Lehrbuch  der  technischen  Chemie,  H.  Ost,  8te  Auf.  257. 


GLASS  199 

percentage  of  pyrolusite  should  be  thus  used.  The  remedy  is  not  a 
permanent  one,  and  if  the  glass  is  exposed  to  the  sunlight  for  a  long 
time,  it  develops  a  violet  shade,  as  may  often  be  observed  in  the 
window  panes  of  old  houses. 

Arsenious  acid  (As2Oa),  or  nitre  (NaNOa),  is  often  added  to  the 
materials  for  colorless  glass.  The  former  is  reduced  to  metallic 
arsenic,  which  volatilizes.  It  affords  a  very  clear  and  lustrous  glass. 
Zinc  oxide  is  often  used  to  decompose  any  sodium  sulphide,  which 
would  give  a  yellow  tinge  to  the  product. 

In  common  bottle  glass  and  other  cheap  grades,  where  color  is 
no  objection,  blast  furnace  slag  is  often  used.  This  generally  needs 
the  addition  of  soda,  to  render  it  more  fusible  and  plastic. 

The  formulae  for  glass  mixtures  vary  much  in  the  different  fac- 
tories, not  only  because  of  variations  in  the  composition  of  the  glass 
produced,  but  also  because  the  materials  are  of  different  degrees  of 
purity.  These  are  often  empirical  recipes,  not  based  on  analysis  of 
the  raw  materials. 

The  fuel  for  glass  making  is  an  important  item.  A  quick-burn- 
ing material,  yielding  a  long  flame,  without  smoke  or  soot,  is  desir- 
able. For  fine  grades,  wood  is  still  employed  in  some  places,  but 
good  coal  is  now  most  common.  In  this  country  the  discovery  of 
natural  gas  had  a  great  influence  on  the  glass  industry,  and  within  a 
few  years  most  of  the  larger  plants  were  moved  into  the  gas  territory, 
Pittsburgh  becoming  the  centre  of  the  manufacture.  With  the  decline 
of  the  natural  gas  supply,  producer  gas  (p.  41)  or  oil  has  been  substi- 
tuted as  fuel.  Gas  is  an  ideal  fuel  for  this  purpose,  since  it  is  clean, 
easily  managed,  and  gives  a  regular  heat.  It  is  generally  employed 
in  regenerative  furnaces  (Fig.  23,  p.  44).  Crude  petroleum,  or  the 
residuum  from  kerosene  distillation,  is  much  used  and  is  a  good  fuel. 
Whatever  the  mode  of  heating,  only  the  flame  and  hot  gases  should 
come  in  contact  with  the  pots  or  their  contents. 

There  are  several  forms  of  glass-furnaces.  The  common  pot  fur- 
nace has  the  pots  placed  in  a  circle  around  a  central  opening  in  its 
bed,  through  which  the  flame  and  hot  gases  come  up  'from  the  grate, 
which  is  below  the  hearth.  The  furnace  is  roofed  with  a  rather  flat 
arch,  which  deflects  the  flame  down  upon  and  around  the  pots.  When 
open  pots  are  used,  it  is  essential  that  no  soot  or  smoke  enter  the  fur- 
nace, and  much  care  is  necessary  in  firing.  In  some  forms,  the  fuel  is 
introduced  by  mechanical  means  from  beneath  the  grate,  so  that  the 
fire  burns  on  top  of  the  pile  of  coal.  This  prevents  the  entrance  of 
cold  air  into  the  furnace,  and  also  consumes  all  smoke. 


200 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


The  Boetius  furnace  (Fig.  82)  is  used  abroad,  and  is  best  adapted 
for  closed  pots.  Coal  or  coke  is  charged  at  (A),  and  air  enters  through 
(B,  B).  The  flame  passes  through  (C)  into  the  upper  compartment  (D), 

containing  the  pots.  The  prod- 
ucts of  combustion  escape 
through  (E,  E). 

Siemens  gas  furnace  (Fig. 
23,  p.  44)  is  much  used  because 
of  its  economy  of  fuel,  both  as 
a  pot  furnace  and  as  a  tank- 
furnace.  The  last  named  is 
more  economical  where  a  large 
quantity  of  one  kind  of  glass 
is  to  be  made.  It  replaces  the 

FIG.  82.  .  ' 

expensive  and  tragile  pots  by  a 

single  large  deep  hearth  or  tank,  at  one  end  of  which  the  raw  materials 
are  continually  introduced,  while  the  glass  is  withdrawn  at  the  other. 
Figure  83  shows  a  plan  and  elevation  of  a  tank-furnace,  in  which  the 


FIG.  83. 

batch  is  introduced  at  (A).  The  gas-flame  issues  from  (C,  C)  and 
plays  over  the  surface  of  the  charge.  The  batch  (B)  soon  fuses  and 
the  liquid  mass  flows  towards  the  opposite  end  of  the  tank.  At  (F) 
are  elliptical  "  floaters  "  of  fire-clay,  one  end  of  which  rests  in  recesses 
in  the  wall,  while  the  free  ends  meet  in  the  middle  of  the  furnace. 
The  current  of  melted  glass  flowing  towards  (D)  constantly  presses 
these  floaters  together  and  prevents  their  separation.  The  liquid 
mass  thus  passes  under  the  floaters  and  collects  in  the  compartment 


GLASS 


201 


(D),  from  which  it  is  withdrawn  through  the  openings  (E,  E).  At 
(B)  the  temperature  is  very  high,  and  as  the  glass  flows  slowly  towards 
(F),  the  refining  takes  place.  In  (D)  the  temperature  is  lower  and 
the  glass  has  cooled  sufficiently  for  working.  The  impurities,  rising 
to  the  surface  during  the  melting  and  refining,  are  retained  by  the 
floaters  so  that  the  glass  in  (D)  has  a  clean  surface  and  is  free  from 
bubbles.  Small  rings  of  fire-clay  may  be  kept  floating  on  the  glass 
near  the  working  doors  (E,  E) ;  by  dipping  the  glass  from  the  centre 
of  these  rings,  it  is  obtained  free  from  any  impurities  which  may  be 
on  the  surface  of  the  melt  in  (D).  A  typical  furnace  of  this  kind  may 
be  about  75  feet  long  by  16  feet  wide  and  5  feet  deep,  to  the  level  of 
the  doors  (E,  E). 

Glass-furnaces  must  be  made  from  very  refractory  materials. 
The  dome  and  arches  are  usually  silica,  or  Dinas  bricks,  or  ganister, 
but  the  bed  is  generally  fire-clay,  as  this  is  less  attacked  by  the  con- 
tents of  a  pot  when  one  breaks.  The  life  of  a  furnace  is  very  uncer- 
tain, but  may  be  several  years.  If  allowed  to  ^_ 
cool,  it  is  generally  necessary  to  reline  it  before  CjSilMh  4B58 
starting  again. 

Pots  for  glass  making  are  very  carefully  con- 
structed, only  the  best  material  being  used. 
The  breaking  of  a  pot  in  the  furnace  is  a  seri- 
ous matter,  often  resulting  in  the  loss  of  the 
glass  and  there  is  more  or  less  loss  of  time. 

Glass-pots  are  of  two  kinds,  open  and  closed. 
Open  pots  (Fig.  84)  are  circular  vessels,  about  as  wide  as  they  are 
deep,  i.e.  from  3  to  5  feet,  and  usually  slightly  broader  at  the  top 

than  on  the  bottom. 
They  are  preferred  for 
a  quick  melt,  and 
are  generally  used  for 
glass  which  contains 
no  lead. 

Closed  pots  (Fig. 
85)  are  usually  longer 
in  one  direction,  and 
are  about  5  feet  by  3j  feet,  by  4  feet  high.  The  neck  of  the  opening 
is  built  into  the  wall  of  the  furnace  in  such  a  manner  that  neither 
flame  nor  fire  gases  can  come  into  contact  with  and  injure  the  glass, 
and  consequently  cheaper  fuel  may  be  used ;  but  these  pots  heat 
more  slowly  than  do  open  ones.  They  are  always  used  for  lead  glass. 


FIG.  84. 


FIG.  85. 


202  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

Clay  rings  are  sometimes  placed  in  the  pots,  so  that  the  glass 
may  be  withdrawn  without  contamination  from  the  floating  impuri- 
ties. Sometimes  a  partition  is  constructed  across 
the  pot  (Fig.  86),  the  raw  materials  being  intro- 
duced and  melted  on  one  side,  and  the  refined 
glass,  free  from  impurities,  having  passed  under 
the  partition,  is  worked  out  on  the  other  side. 

The  material  of  the  pots  is  fire-clay ;  but  the 
necessary  degree  of  plasticity,  with  the  required 
infusibility,  are  possessed  by  but  few  clays.  To 
avoid  excessive  shrinkage  when  the  new  pot  is 
heated,  a  large  proportion  of  burned  clay  from  old  pots,  entirely  free 
from  any  adhering  glass  and  ground  to  a  coarse  powder,  is  mixed 
with  the  new  clay.  The  mass  is  then  moistened  and  well  kneaded 
by  treading,  and  is  then  allowed  to  stand  and  "  age  "  for  a  long 
time,  to  increase  the  plasticity.  The  pots  are  built  up  by  hand,  the 
bottom  being  formed  first,  and  the  sides  constructed  on  it.  The  clay 
is  laid  on  in  small  lumps,  and  each  lump  is  carefully  pressed  into 
place  by  the  workman  before  another*  is  added.  From  three  to  five 
inches  is  usually  added  to  the  height  of  the  pot  each  day.  When 
finished,  it  is  allowed  to  stand  in  a  room  at  constant  temperature  and 
protected  from  draughts  of  air,  for  several  months,  to  dry  thoroughly. 
In  order  to  prevent  too  rapid  drying,  which  might  cause  cracking,  it 
is  generally  covered  with  canvas  or  paper  for  the  first  few  weeks. 

Before  placing  it  in  the  glass-furnace,  a  new  pot  is  heated  very 
slowly  in  a  special  furnace,  until  it  is  brought  up  to  the  temperature 
of  the  former,  into  which  it  is  then  transferred,  while  still  hot,  through 
an  opening  in  the  wall.  The  wall  must  be  taken  down,  the  broken 
pot  removed,  and  the  new  one  introduced,  without  allowing  the  fur- 
nace to  cool ;  hence  the  operation  is  difficult,  and  requires  much  skill 
on  the  part  of  the  workmen.  Once  introduced,  a  pot  is  kept  in  con- 
stant use,  and  never  allowed  to  cool ;  for,  if  it  should,  it  would  crack 
when  heated  again.  Its  life  is  very  uncertain,  but  a  good  one  will 
sometimes  last  for  months.  The  first  charge  in  a  new  pot  is  broken 
glass  (cullet),  which  forms  a  glaze  over  the  surface  and  protects  it 
from  the  solvent  action  of  the  melted  raw  materials. 

The  general  process  of  glass  making  is  as  follows :  The  finely 
ground  raw  materials  are  thoroughly  mixed,  sometimes  by  regrinding 
the  mixture  or  "  batch."  The  batch  is  shovelled  into  the  pot,  together 
with  a  certain  amount  of  broken  glass  called  "  cullet "  ;  this  melts  at  a 
comparatively  low  temperature,  and  thus  assists  in  liquefying  the  rest 


GLASS 


203 


of  the  charge.  More  of  the  batch  is  added,  until  the  pot  is  filled  to 
the  desired  height  with  the  fused  mass ;  then  volatile  substances,  such 
as  arsenious  acid,  used  in  decolorizing  the  glass,  are  added. 

During  the  melting,  much  gas  (CO2,  SO2,  and  O)  escapes,  and  the 
bubbles  rise  through  the  melt,  stirring  it  and  causing  frothing.  A 
considerable  amount  of  the  alkali  and  other  constituents  volatilize. 
The  reactions  involved  are  variously  written  by  different  authorities : 

(a)  1)  Na2CO3  +  CaCO3  +  2  SiO2  =  Na2Ca(SiO3)2  +  2  CO2.* 

2)  2  Na2SO4  +  2  SiO2  +  C  =  2  NasSiOg  +  CO2  +  2  SO2.* 

3)  Na2SiO3  +  CaCO3  +  SiO2  =  Na2Ca(SiO3)2  +  CO2.* 

(b)  2  Na2SO4  +  6  Si02  +  C  =  2(Na2O,  3  SiO2)  +  2  SO2  +  CO2.f 

When  the  melt  has  come  to  a  state  of  quiet  fusion,  the  tempera- 
ture is  generally  raised  somewhat,  and  the  liquid  glass  allowed  to 
stand  for  a  time.  This  is  called  "  refining,"  and  its  object  is  to  form 
a  homogeneous  mass,  free  from  bubbles  and  bits  of  uncombined  silica 
or  other  matter.  The  scum  which  collects  is  skimmed  off;  it  is 
called  "  glass  gall,"  and  consists  of  undecomposed  sulphates  and  chlo- 
rides of  lime  and  alkali,  alumina  compounds  from  the  pot,  and  various 
other  impurities.  If  too  little  carbon  is  used  in  the  batch,  the  melt  is 
covered  with  a  layer  of  fused  sodium  sulphate ;  this  is  known  to  the 
workmen  as  "  salt  water."  Samples  of  the  glass  are  examined  during 
the  refining,  and  these  determine  the  exact  time  of  heating.  After 
refining,  the  glass  is  too  liquid  to  blow,  or  to  work  to  advantage,  and 
is  cooled  until  it  becomes  pasty. 

The  quantities  of  materials  used  in  the  batch,  for  some  typical 
glasses,  are  shown  in  the  following  table :  — 


SiO* 

NazCOa 

Na2SO4 

CaCOs 

CaO 

MnO2 

Pb304 

K2COa 

COKE 

SLAG 

French  Plate 

100 

34 



14.5 



0.25 









(Soda-lime) 

Bohemian 

100 

— 

— 

— 

18 

— 

— 

40 

— 

— 

(Potash-lime) 

Window 

100 

5 

37.5 

35.8 

— 

0.4 

— 

— 

4 

— 

(Soda-lime) 

Lead  flint 

100 

— 

— 

— 

— 

:  — 

60 

20 

— 

— 

Bottle  glass 

100 

— 

25 

34 

— 

— 

— 

— 

3 

5 

(Green  glass) 

Glass  is  known  under  various  names  in  commerce,  according  to 
the  method  of  its  manufacture  or  the  uses  to  which  it  is  put ;  for  ex- 
ample, plate,  crown,  flint,  and  window  glass. 

*  Wagner,  Chemical  Technology,  608. 

t  Ost.  Lehrbuch  d.  technischen  Chemie,  5*  Auf.,  237. 


204  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

Plate  glass  is  cast  on  a  large  iron  plate  or  "  casting  table,"  made 
up  of  thick,  narrow  segments  of  cast  iron,  bolted  together  and  planed 
on  top.  These  tables  were  formerly  cast  in  one  piece,  and,  being 
large  and  thick,  were  very  expensive.  But  when  put  to  use,  they  soon 
became  warped  and  dished,  owing  to  unequal  expansion  of  the  top 
and  bottom;  this  caused  much  loss  of  time  and  glass  in  the  subse- 
quent grinding  of  the  plate.  The  built-up  table  is  much  cheaper  and 
retains  its  even  surface  much  longer. 

The  melted  glass  is  poured  on  the  table  and  spreads  out  in  an 
even  layer.  But  to  give  the  plate  a  uniform  thickness  and  to  smooth 
down  any  inequalities  of  the  surface,  a  heavy  iron  roller,  travelling  on 
adjustable  guides  at  the  edge  of  the  table,  is  passed  over  it.  The 
height  of  these  guides  determines  the  thickness  of  the  plate.  Both 
the  casting  table  and  the  roller  are  heated  before  use,  so  that  the  glass 
may  not  be  cooled  too  rapidly.  As  soon  as  the  plate  is  rolled,  it  is 
transferred  to  the  floor  of  the  annealing  furnace,  or  "  lehr,"  which  is 
directly  in  front  of  the  casting  table,  and  which  has  been  heated  to  the 
temperature  of  the  glass.  The  floor  of  the  oven  consists  of  a  series  of 
iron  plates  supported  on  rollers ;  as  each  new  sheet  of  glass  is  intro- 
duced the  entire  series  is  moved  forward  towards  the  outlet.  As  the 
furnace  is  heated  only  at  the  inlet  end,  the  temperature  gradually  de- 
creases towards  the  outlet,  and  the  glass  slowly  cools  during  a  number 
of  hours.  All  glass  must  be  annealed.  This  process  probably  allows 
the  molecules  to  arrange  themselves  so  that  there  is  no  considerable 
internal  stress  when  the  mass  is  cold.  Unannealed  glass  which  has 
been  suddenly  cooled  is  always  under  high  internal  strain,  which 
makes  it  exceedingly  brittle,  and  may  even  cause  it  to  fly  to  pieces 
spontaneously,  or  when  slightly  scratched. 

When  removed  from  the  annealing  furnace,  the  plate  is  uneven 
and  rough,  and  may  be  somewhat  devitrified  on  the  surface.  It  is 
fastened  on  a  horizontal  table,  and  heavy  cast-iron  rubbers  are  made 
to  slide  over  its  surface  with  a  rotary  motion,  while  coarse  sand  and 
water  are  sprinkled  on  it.  When  the  glass  is  smoothed  and  of  a  uni- 
form thickness,  it  is  polished  by  rubbing  with  buffers,  covered  with 
leather  or  felt,  and  used  with  fine  emery  dust  or  putty  powder.  About 
one-half  of  the  thickness  of  the  plate  is  cut  away  during  the  grinding 
and  polishing. 

Plate  glass  is  usually  a  soda-lime  glass.  The  batch  is  melted  and 
refined  as  has  been  described,  great  care  being  taken  to  remove  all 
the  "  gall/'  which  is  skimmed  off  immediately  before  the  casting.  An 
especially  strong  pot  is  used,  which  will  stand  the  strain  of  lifting 


GLASS  205 

from  the  furnace  while  full  of  melted  glass.  The  furnace  is  constructed 
with  brick-lined,  cast-iron  doors,  which  open  to  permit  the  removal  of 
the  pot.  The  melting  and  annealing  furnaces  are  often  joined,  so 
that  the  latter  may  be  heated  with  waste  heat. 

The  chief  uses  of  plate  glass  are  for  windows  and  mirrors.  A  con- 
siderable quantity  of  "  rough  plate,"  unground,  as  it  comes  from  the 
annealing  furnace,  is  used  for  skylights  and  for  flooring. 

Window  glass  is  always  blown.  It  is  usually  a  soda-lime  glass, 
and  the  batch  is  melted  and  refined  in  the  usual  manner,  either  in 
pots  or  in  tanks.  After  the  refining,  the  glass  is  allowed  to  become 
pasty,  and  then  the  blower  begins  his  work.  His  chief  tool  is  the 
"  pipe,"  a  straight  piece  of  iron  tubing,  four  or  five  feet  long,  usually 
provided  with  a  mouthpiece.  He  dips  the  pipe  into,  the  soft  glass, 
which  is  called  "  metal,"  and  gathers  a  lump  on  the  end.  Then,  by 
blowing  through  the  pipe,  while  whirling  it  between  the  palms  of  his 
hands,  he  forms  a  hollow  globe  of  glass.  This  is  reheated  in  a  special 
furnace  ("glory-hole")  until  soft,  rolled  on  a  flat  surface,  and  then 
swung  in  a  vertical  circle,  with  occasional  blowing  through  the  pipe, 
until  the  globe  has  elongated  into  a  hollow  cylinder,  closed  at  one 
end  and  opening  into  the  pipe  at  the  other.  In  order  to  have 
plenty  of  room  for  the  vertical  swinging,  the  workman  stands  on  a 
bridge  placed  across  a  rather  deep  pit.  The  closed  end  of  the  cylinder 
is  reheated  until  soft,  and  then. blown  out;  the  small  opening  thus 
made  is  enlarged  by  means  of  the  "  widening  tongs."  The  pipe  is 
detached  by  touching  its  point  of  attachment  with  a  wet  stick,  and 
the  edges  of  the  still  soft  glass  are  trimmed  with  shears.  A  hollow 
cylinder,  open  at  both  ends,  is  thus  formed,  and  is  cut  lengthwise 
with  a  diamond.  It  is  then  put  into  the  flattening  furnace,  in  such  a 
position  that  the  cut  is  on  the  upper  side.  The  heat  being  sufficient 
to  soften  the  glass,  the  cylinder  slowly  opens,  and  spreads  out  on  the 
floor  of  the  furnace  in  a  flat  sheet.  It  is  then  transferred  to  the  an- 
nealing furnace  for  blown  ware.  This  consists  of  a  long  oven,  heated 
at  one  end  and  cool  at  the  other.  A  system  of  endless  iron  bands 
carries  the  glass  slowly  from  the  hot  to  the  cool  end  of  the  oven. 
Sometimes  the  glass  to  be  annealed  is  placed  on  a  large  horizontal 
table,  usually  built  of  slabs  of  stone,  and  carefully  balanced,  so  as  to 
revolve  easily  and  slowly,  by  means  of  a  gear,  while  a  segment  passes 
through  a  narrow  opening  in  the  side  of  the  flattening  furnace,  where 
it  is  exposed  to  the  high  temperature.  The  glass  is  thus  slowly  carried 
out  of  the  furnace  into  a  cooler  compartment,  from  which  it  is  re- 
moved when  nearly  cold.  This  table  is  chiefly  used  for  window  glass. 


206  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

The  glass  sheets  are  now  cut  to  marketable  size,  without  any  polish- 
ing. As  the  surface  of  blown  glass  is  fused  and  not  polished,  it  is 
brilliant  and  hard ;  hence,  it  is  less  easily  scratched  or  etched,  and  is 
more  durable  than  plate  glass  when  exposed  to  the  weather. 

Glass-blowing  is  an  exceedingly  fatiguing  labor,  and  only  men  of 
strong  constitution  and  good  lung  power  can  do  it.  The  mass  of 
glass  which  a  good  workman  will  handle  at  one  time  averages  about 
18  pounds,  and  from  it  he  will  form  a  cylinder  over  a  yard  long  and  a 
foot  in  diameter.  A  skilful  glass-blower  can  form  all  kinds  of  glass 
utensils  by  the  use  of  his  pipe  and  other  tools.  Wine  glasses,  tumblers, 
bottles,  and  lamp  chimneys,  for  example,  are  often  entirely  blown. 
But  much  glass  ware  is  blown  in  moulds,  or  pressed.  Glass-blowing 
machines  are  now  in  use  for  common  bottles,  lamp  chimneys,  fruit 
jars,  etc.,  and  in  some  cases  window  glass,  carboys,  and  other  large 
articles  are  machine  blown. 

Crown  glass  is  a  form  of  blown  glass  in  which  the  globular  balloon 
first  blown  is  flattened  by  pressing  against  a  flat  surface.  The  end 
of  an  iron  rod  is  smeared  with  a  coating  of  melted  glass  and  attached 
to  the  centre  of  the  flattened  surface.  The  pipe  is  then  detached, 
leaving  a  small  hole.  By  reheating  and  rotating  the  rod  swiftly 
about  its  longitudinal  axis,  the  balloon  opens  out,  forming  a  circular 
plate  or-  disk,  4  or  5  feet  in  diameter  with  the  rod  at  the  centre.  But 
they  are  not  of  the  same  thickness  at  the  edge  and  middle ;  where  the 
rod  was  attached,  there  is  a  thick  rounded  mass  called  the  "  bull's- 
eye."  This  must  be  cut  out, 'so  large  window  panes  cannot  be  made 
from  crown  glass.  Thus  it  is  not  an  economical  form  of  glass-blowing, 
and  the  industry  is  practically  abandoned.  A  little  is  now  made  to 
supply  a  small  demand  for  the  "  bull's-eyes  "  for  decorative  purposes. 
Crown  glass  has  a  very  brilliant  surface. 

Flint  glass  now  means  any  transparent,  colorless  glass. 

In  cut-glass  ware,  the  design  is  cut  in  the  solid  glass,  which  has 
been  given  its  general  form  by  blowing  or  pressing.  Sometimes  the 
design  is  formed  in  the  pressed  ware,  and  the  surface  only  is  cut  and 
polished.  Glass-cutting  is  done  on  a  soft  steel,  copper,  or  sandstone 
wheel,  the  cutting  edge  of  which  is  fed  with  sand  or  emery  and  water. 
The  polishing  is  done  on  similar  wheels  of  wood,  fed  with  rouge  or 
putty  powder.  Lead  glass  is  nearly  always  used  for  cutting,  since  it  is 
softer  and  more  brilliant  than  other  varieties. 

Pressed  glass  is  made  by  the  use  of  a  die  or  mould ;  these  moulds 
are  expensive,  but  owing  to  the  great  mumber  of  pieces  of  the  same 
form  and  design  that  are  made  with  slight  labor,  pressed  ware  is  cheap. 


GLASS  207 

"  Tough  "  or  "  tempered  "  glass  is  produced  by  a  special  method 
of  annealing,  the  articles  so  treated  being  capable  of  withstanding 
blows  and  sudden  changes  of  temperature.  This  tempering  is  done 
by  plunging  the  article,  while  still  so  hot  as  to  be  somewhat  soft,  into  a 
bath  of  oil  heated  to  100°-300°  C .  This  sudden  "  quenching  "  hardens 
the  surface  of  the  glass,  but  causes  internal  stresses.  If  scratched  or 
cut  slightly,  toughened  glass  is  apt  to  fly  to  pieces,  sometimes  with  great 
violence.  And  even  after  standing  a  long  time  spontaneous  fracture 
often  occurs.  It  is  mainly  used  for  lamp  chimneys. 

A  process  for  making  hardened  glass  plates  and  window  lights  is 
employed  in  which  cold  metallic  surfaces  are  applied  to  the  glass 
plates  while  the  latter  are  still  plastic.  The  sudden  chilling  imparts 
an  exceedingly  hard  surface  to  the  glass,  so  that  it  can  be  used  in 
exposed  situations,  such  as  in  street  lamps. 

A  compound  glass  is  a  recent  invention  to  replace  the  hardened 
or  tempered  glass.  Articles  are  formed  of  two  layers  of  glass,  the 
inner  layer  having  a  low  coefficient  of  expansion  while  the  outside 
layer  has  a  high  coefficient.  This  glass  is  particularly  recommended 
for  lamp  chimneys  and  chemical  vessels  which  must  endure  sudden 
changes  of  temperature.  The  ratio  between  the  two  coefficients  must 
be  very  carefully  maintained. 

Colored  glasses  are  produced  by  adding  to  the  ordinary  batch  cer- 
tain metallic  oxides  or  salts,  or  even  finely  pulverized  metal.  These 
dissolve  in  the  glass,  and  impart  a  characteristic  color. 

Green  glass  is  produced  by  the  use  of  ferrous  oxide,  chromic 
oxide,  or  a  mixture  of  cupric  and  iron  or  chromium  oxides.  The 
color  produced  by  ferrous  oxide  is  a  dull  green,  of  no  particular 
beauty.  Copperas  or  iron  filings  are  added  to  the  batch  to  form 
the  ferrous  silicate  necessary  for  the  color.  Chromic  oxide  (Cr2O3) 
imparts  a  better  green.  It  is  usually  produced  by  adding  potassium 
bichromate  (K^C^Oy)  to  the  batch.  If  an  excess  of  chromium  oxide 
is  present,  the  uncombined  portion  separates  as  minute  crystals,  dis- 
seminated through  the  glass,  producing  chrome  aventurine.  A  mix- 
ture of  cupric  and  ferric  oxides  produces  green  glass,  owing  to  the 
combined  effect  produced  by  these  oxides  individually. 

Yellow  or  amber  glass  is  made  by  adding  sulphur  or  carbonaceous 
matter  to  the  batch,  producing  sodium  or  potassium  sulphides,  which 
color  the  glass.  A  common  method  is  to  introduce  wood  or  charred 
horn  into  the  melted  glass.  Cadmium  sulphide  is  sometimes  employed. 
No  sulphur  compound  can  be  used  with  lead  glass.  A  rich  yellow 
stain  is  obtained  by  the  use  of  metallic  silver  or  silver  chloride ;  this 


208  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

is  much  used  in  making  church  windows,  and  was  known  in  the  Middle 
Ages.  A  peculiar  greenish  yellow,  fluorescent  glass  is  produced  with 
uranium  oxide,  but  it  is  expensive. 

Orange  glass  of  various  shades  is  made  by  adding  selenium  (as  a 
selenate  with  a  reducing  agent),  or  a  mixture  of  ferric  oxide  and  man- 
ganese dioxide. 

Blue  glass  is  made  with  cobaltic  oxide  (€0203)  or  cupric  oxide.  A 
very  small  percentage  (0.1)  of  cobaltic  oxide  produces  a  deep  blue 
color.  If  more  than  5  per  cent  is  used,  the  color  is  so  deep  that  the 
glass  may  be  ground  for  pigment  (smalt).  Owing  to  the  intensity  of 
its  color,  cobalt  glass  is  much  used  for  "  flashing  "  on  the  surface  of 
colorless  glass.  To  do  this,  the  blower  dips  his  pipe  into  the  pot  of 
colored  glass,  and,  collecting  a  small  lump,  dips  it  into  the  pot  of  color- 
less glass,  or  vice  versa.  By  blowing  he  forms  a  sheet  of  colorless 
glass  which  is  coated  on  one  side  with  a  very  thin  layer  of  colored 
glass,  both  firmly  welded  together.  Both  glasses  must  have  the 
same  composition  and  the  same  coefficient  of  expansion.  A  light 
greenish  blue  is  obtained  by  the  use  of  a  small  quantity  of  cupric 
oxide. 

Violet  is  produced  by  a  small  amount  of  pyrolusite,  free  from  iron. 
An  excess  of  manganese,  especially  if  much  iron  is  present,  gives  a 
deep  yellow  or  brown. 

Red  glass  is  made  with  metallic  gold  or  copper,  cuprous  oxide,  or 
selenium  oxide.  Gold  yields  a  bluish  red,  while  copper  and  selenium 
give  deep  ruby  red.  For  gold  ruby  a  minute  quantity  of  gold  chloride 
is  added  to  the  batch;  on  cooling  the  glass  is  colorless  or  reddish 
yellow.  The  ruby  color  appears  on  reheating  and  is  due  to  colloidal 
precipitation  of  metallic  gold  in  the  glass ;  if  overheated  the  color 
changes  to  a  dull  red  brown,  owing  to  coagulation  of  the  colloidal  gold. 
Gold  ruby  is  generally  "flashed,"  owing  to  its  intense  color. 

For  copper  ruby,  cuprous  oxide  (Gu2O)  as  "hammer  scale,"  is  used  ; 
a  small  quantity  of  iron  filings  may  be  added  to  reduce  any  cupric 
oxide.  The  pot  metal  is  also  nearly  colorless  or  pale  green  and  re- 
quires careful  reheating  to  develop  the  colloidal  copper  precipitate. 
This  glass  is  also  used  for  "flashing." 

Selenium  oxide  yields  a  beautiful  deep  red  in  the  pot  metal,  thus 
avoiding  the  troublesome  second  heating ;  but  the  color  is  less  intense 
than  with  gold  or  copper,  and  flashing  is  not  employed. 

White,  "  opal,"  or  "  milk  "  glass  is  made  by  adding  cryolite  or 
fluorite,  with  felspar,  to  the  batch  for  common  glass.  Calcium  phos- 
phate, as  bone-ash,  may  also  be  used.  These  substances  crystallize 


GLASS  209 

in  the  glass  when  the  melt  is  kept  near  its  fusion  point  for  some  time, 
and  thus  cause  the  opalescence.  Large  quantities  of  tin  or  zinc 
oxides  produce  a  translucent  milk  glass. 

Black  glass  is  obtained  by  using  a  large  excess  of  pyrolusite,  iron, 
or  copper  oxides.  The  so-called  "smoked  glass,"  used  for  optical 
purposes,  contains  some  nickel. 

Enamel  is  an  easily  fusible  glass,  usually  containing  lead  and 
boric  acid,  or  phosphate  or  stannate  of  sodium  or  potassium.  It  is 
usually  white,  blue,  or  gray,  the  color  being  produced  by  adding 
proper  oxides.  It  is  used  for  coating  metallic  (iron)  vessels,  pottery, 
(tiles,  flower-pots,  bricks,  etc.),  and  porcelain.  For  cooking  vessels 
it  must  be  free  from  lead,  and  is  composed  of  sand,  borax,  soda,  and 
calcium  phosphate  or  white  clay  (kaolin).  Enamel  must  have  a  co- 
efficient of  expansion  about  equal  to  that  of  the  iron  on  which  it  is 
placed,  otherwise  the  glaze  is  soon  destroyed  by  heating  and  cooling. 

Iridescent  glass  is  made  by  exposing  the  hot  glass  to  the  vapors 
of  stannic  chloride  (SnCU),  or  hydrochloric  acid;  these  attack  the 
surface  of  the  glass  and  alter  its  composition.  It  was  formerly  sup- 
posed that  the  art  of  making  this  glass  was  invented  by  the  Romans, 
and  later  was  lost.  However,  the  old  Roman  glass  was  not  originally 
iridescent,  but  has  become  so  through  exposure  to  dampness  and 
carbon  dioxide.  The  surface  has  been  partly  decomposed,  the  alkali 
dissolving,  thus  producing  a  thin  layer  of  glass  having  a  different  com- 
position and  physical  structure  from  the  main  body.  This  thin  film 
causes  interference  of  the  light  rays  and  produces  a  play  of  colors 
when  viewed  in  different  positions. 

Mirrors  were  formerly  coated  with  an  amalgam  of  tin.  Tin  foil 
was  covered  with  mercury,  and  the  glass,  carefully  cleaned,  was  laid 
on  the  amalgam,  excess  of  mercury  being  forced  out  at  the  sides,  and 
the  amalgam  adhering  firmly  to  the  glass. 

But  the  silver  mirror  is  now  the  only  kind  made.  A  coating  of 
metallic  silver  is  deposited  on  the  glass  from  an  ammoniacal  solution 
of  silver  nitrate  by  the  use  of  a  reducing  agent.  Ammonium  tartrate, 
or  a  solution  of  glucose  or  milk  sugar  in  caustic  soda,  is  generally 
used  for  this  purpose ;  or  aldehyde  is  sometimes  used.  The  glass  is 
carefully  cleaned  and  covered  with  the  silver  solution  containing  the 
reducing  substance,  ^nd  heated  gently  on  a  steam  or  hot-air  bath. 
The  thin  layer  of  metallic  silver  deposited  adheres  to  the  glass,  and 
is  washed  and  dried,  and  covered  with  a  protecting  varnish  to  pre- 
vent the  hydrogen  sulphide  in  the  air  from  tarnishing  the  reflecting 
surface. 


210  OUTLINES   OF    INDUSTRIAL   CHEMISTRY 

Plate  glass  is  generally  used  for  the  best  mirrors.  Blown  glass, 
which  is  used  for  the  cheaper  ones,  is  very  apt  to  contain  bubbles 
and  strise,  causing  distortion  of  the  image. 

Tradition  assigns  the  discovery  of  glass  to  the  Phoenicians.  Glass 
making  is  a  very  old  industry,  and  was  known  to  the  early  Egyp- 
tians, since  glass  beads  have  been  found  in  mummy  cases  at  least  3000 
years  old.  Glass  articles  have  also  been  found  in  the  excavations  at 
Nineveh.  From  Egypt,  the  industry  was  transferred  to  Rome,  and 
on  the  fall  of  the  Western  Empire  the  art  was  carried  to  Byzantium. 
Byzantine  glass  attained  a  high  degree  of  perfection  ;  but  in  the  middle 
of  the  thirteenth  century  Venice  became  the  centre  of  the  industry, 
and  Venetian  glass-blowers  were  remarkably  expert  in  the  production 
of  beautiful  and  delicate  patterns.  Finally,  Bohemia  took  the  lead 
in  the  manufacture  of  glass,  and  has  retained  a  front  rank  ever 
since. 

Window  glass  was  made  by  the  Romans  to  a  small  extent,  and 
specimens  of  such  glass  were  taken  from  the  ruins  of  Pompeii.  In 
England,  it  first  came  into  use  in  houses  during  the  reign  of  Elizabeth, 
but  previously  to  this  it  had  been  used  in  cathedrals  and  churches. 
From  the  records  of  York  cathedral,  it  is  shown  that  during  the  time 
of  Archbishop  Wilfrid  (669-709  A.D.)  "  glass  was  placed  in  the  win- 
dows so  that  birds  could  no  longer  fly  in  and  out  and  defile  the  sanc- 
tuary." The  contract  for  the  glass  in  the  great  West  Window,  given 
by  Archbishop  Melton,  is  dated  1330.  The  work  was  finished  before 
1350,  and  the  price  paid  was  6d.  per  square  foot  for  white,  and  Is. 
per  square  foot  for  colored  glass.  This  window  is  54  feet  high  by  30 
wide,  and  is  to-day  regarded  as  one  of  the  finest  examples  of  stained 
glass  in  England.  The  great  East  Window  (77  feet  high  and  32  feet 
wide)  was  glazed  by  John  Thornton  in  1405-1408,  for  which  he  re- 
ceived 4s.  per  week.  These  examples  demonstrate  the  high  degree 
of  perfection  to  which  the  glass  industry  had  advanced  during  the 
Middle  Ages. 

At  the  present  time,  Belgium  and  England  lead  in  the  production 
of  window  and  plate  glass,  while  Germany,  France,  and  the  United 
States  also  manufacture  enormous  quantities.  Austria  and  Germany 
are  the  leading  producers  of  blown  ware. 


GLASS  211 


REFERENCES 

Glass  Making.     Powell,  Chance  and  Harris.     1883. 

U.  S.  Census,  1880.  —  Report  on  the  Manufacture  of  Glass.     J.  D.  Weeks. 
Die  Glas-Fabrikation.     R.  Gerner,  Vienna,  1880.     (Hartleben.) 
Handbuch  der  Glas-Fabrikation.     Dr.  E.  Tscheuschner,  Weimar,  1885. 

(Voigt.) 
Die  Fabrikation  und  Raffinirung  des  Glases.     Wilhelm  Mertens,  Vienna, 

1889.     (Hartleben.) 
Verre  et  Verrerie.     L.  Appert  et  Jules  Henri vaux,  Paris,  1894.     (Gau- 

thiers-Villars  et  Fils.) 
Journal    of    the    Franklin    Institute.     1887.     Glass    Making.  —  C.    H. 

Henderson. 
Proceedings  of  Engineers'  Society  of  Western  Pennsylvania.     1895,  119. 

A  Study  of  Glass.  —  Robert  Linton. 

Elements  of  Glass  and  Glass  Making.     B.  F.  Riser.     1899. 
Jena  Glass.     H.  Hovestadt.     1902. 
Journal  of  the  American  Chemical  Society.     1902,  893.     G.  E.  Barton. 


CERAMIC   INDUSTRIES 

Clays  are  natural  hydrated  silicates  of  aluminum,  formed  by  the 
weathering  of  felspar  or  felspathic  rocks,  such  as  granite.  The  hy- 
drolysis of  felspar  may  be  represented  thus :  — 

A12O3,  K2O,  6  SiO2  +  CO2  +  2  H2O  = 

A12O3,  2  SiO2  •  2  H2O  +  K2CO3  +  4  SiO2. 

Clays  which  have  not  been  transported  by  natural  waters  from 
the  place  where  they  were  formed  are  called  primary;  secondary  clays 
have  been  washed  from  their  original  beds  and  deposited  elsewhere. 
Primary  clay  derived  from  pure  felspar  contains  little  impurity  other 
than  silica,  and  is  called  kaolin,  or  China  clay.  It  is  a  white,  powdery 
mass,  essentially  hydrated  silicate  of  aluminum  and  silica,  nearly  all 
the  alkali  having  been  leached  out.  Kaolin  is  characterized  by  its 
capacity  to  undergo  progressive  hydration  in  contact  with  water ;  in 
the  early  stages  this  hydration  is  merely  on  the  surface  of  the  particles, 
but  as  it  penetrates  deeper  and  becomes  more  complete,  the  clay  as- 
sumes markedly  colloidal  properties.  Its  aqueous  suspensions  become 
tolerably  permanent  (e.g.  river  silt),  and  in  the  solid  state  it  is  very 
plastic,  i.e.  it  can  be  readily  moulded,  and  surfaces  pressed  together 
coalesce.  The  water  of  hydration  can  be  driven  off  by  heat,  where- 
upon the  plasticity  is  lost,  and  the  mass  becomes  hard  and  stonelike. 
These  facts  are  the  basis  of  the  ceramic  industry. 

The  rocks  from  which  primary  clays  are  formed  are  seldom  homo- 
geneous, and  the  various  components  have  different  rates  of  decom- 
position and  hydration.  Tne  clay  then  consists  of  a  mixture  of 
particles  of  different  composition  and  colloidal  character.  The 
formation  of  secondary  clays  usually  involves  mixing  of  various  pri- 
mary deposits,  and  the  particles  of  such  clays  are  more  diverse  in 
character.  Kaolin  itself  is  almost  infusible,  but  if  the  clay  contains 
in  an  appreciable  amount  particles  of  low  melting  point  (unweathered 
felspar,  quartz,  and  metallic  oxides),  on  heating,  these  finely  divided 
particles  disseminated  in  the  mass  serve  as  a  flux  for  the  rest  of  the 
clay,  and  cause  it  to  soften,  or  even  to  melt,  at  temperatures  far  below 
the  fusion  point  of  the  major  part  of  the  mass.  Thus  a  clay  may  be 
of  such  composition  that  if  rendered  homogeneous  (e.g.  by  melting) 
its  fusion  point  is  very  low,  but  in  the  clay  itself  none  of  the  various 

212 


CERAMIC   INDUSTRIES  213 

particles  are  of  low  fusion  point ;  such  a  clay  will  soften  only  at  very 
high  temperatures,  but  once  softening  begins,  the  mass  will  quickly 
liquefy. 

Very  difficultly  fusible  clays  are  generally  primary,  as  among 
the  constituent  particles  of  secondary  clays,  some  are  likely  to  be  of 
low  melting  point.  Fire-clays  are  very  difficultly  fusible.  They  are 
usually  found  underlying  coal  beds.  In  composition  they  are  kao- 
lins containing  free  silica  as  quartz.  They  may  contain  a  little  more 
iron  than  good  China  clay,  but  are  free  from  alkalies. 

Secondary  clays  have  had  more  opportunity  for  thorough  hydra- 
tion  than  primary,  and  are  hence  more  plastic ;  these  colloidal  clays 
are  called  pipe-  or  ball-clays,  and  are  also  known  as  "  fat  "  clays  to 
distinguish  them  from  the  non-plastic  or  "  lean  "  clays. 

Fat  clays  absorb  much  water  and  have  great  binding  power,  so 
that  they  are  easily  shaped  by  the  potter.  But  on  drying,  and  es- 
pecially when  burned,  they  shrink  much.  This  shrinkage  is  coun* 
teracted  by  mixing  with  the  fat  clay  a  certain  amount  of  "leaning" 
material,  such  as  silica,  pulverized  burned  clay,  or  "  grog,"  the  ground, 
unglazed  body  of  pottery.  Fat  clays  are  usually  more  fusible  than 
lean  clays. 

Highly  hydrated,  plastic  clays  can  lose  a  large  part  of  their  water 
without  much  modification  of  structure,  if  dried  at  temperatures 
below  100°  C.  They  still  rehydrate  if  wet.  All  clays  lose  water 
of  chemical  composition  below  a  red  heat,  and  then  lose  capacity  for 
rehydration  and  plasticity.  All  stages  of  dehydration  are  accom- 
panied by  shrinkage,  roughly  proportional  to  the  original  plasticity ; 
if  excessive,  this  causes  cracks  in  drying  and  burning ;  it  is  controlled 
by  mixing  plastic  with  non-plastic  clays,  or  "  grog."  Since  the  physi- 
cal properties  of  the  product  are  determined  by  the  proportions  of 
the  various  clays  employed,  in  making  ware  to*  meet  definite  require- 
ments, a  complex  mixture  of  clays  is  usually  necessary. 

Clay  is  used  in  all  degrees  of  hydration ;  in  the  form  of  a  colloidal 
suspension,  or  "  slip,"  it  makes  possible  the  forming  of  articles  by 
"  casting  "  in  plaster  moulds ;  when  dehydrated  to  the  form  of  a 
plastic  solid  mass,  it  is  used  on  the  potter's  wheel.  Dried  at  a  low 
temperature,  it  loses  its  plasticity  and  becomes  hard,  as  in  sun- 
dried  bricks  (adobe) ;  it  loses  chemically  combined  water  below  a 
red  heat,  and  an  association  of  the  aggregates  occurs,  which  renders 
it  inert  and  incapable  of  rehydration;  at  higher  temperatures,  the 
particles  of  lowest  melting  point  fuse  and  cement  together  the  remain- 
ing granules ;  finally  fusion  may  go  so  far  that  the  mass  becomes  semi- 


214 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


vitreous,  but  complete  fusion  is  avoided  to  prevent  deformation  of 
shape. 

Because  of  their  nature  and  origin,  clays  are  complicated  mix- 
tures, each  component  differing  in  chemical  behavior  for  varying 
degrees  of  hydration;  hence  neither  the  empirical  analysis,  nor  the 
so-called  "  rational  analysis  "  is  of  much  value  to  the  potter.  The 
latter  is  a  determination  of  "clay  substance"  or  kaolin,  felspar, 
quartz,  etc.  (by  their  different  behavior  to  solvents)  and  merely 
emphasizes  the  differences  between  clays.  The  plasticity,  fusibility, 
shrinkage,  and  color  of  the  product  after  burning,  and  its  coefficient 
of  expansion  are  the  important  properties,  and  these  must  be  experi- 
mentally determined  for  each  clay.  The  variations  in  clays  are 
shown  in  the  following  analyses  :  — 

CHEMICAL  ANALYSES 


GERMAN* 

(SENNEWITZ) 

BOHEMIAN* 
(ZETTLITZ) 

VlKGINIANf 

(KAOLIN) 

Omof 
(FIRE-CLAY) 

ENGLISH  f 

(CORNISH 

STONE) 

SiO2         .... 

64.9 

23.8 
0.8 

0.5 
1.4 

8.4 

45.6 
39.0 
0.5 
0.6 
0.1 
0.5 
13.6 

50.02 
35.18 
0.36 
0.12 
0.07 
3.39 
10.57 

74.93 
17.19 
0.79 
0.29 
0.46 
1.61 
5.44 

73.57 
16.48 
0.27 
1.17 
0.21 
5.84 
2.45 

A1203  
Fe-fOt 

CaO    .     .     .     .     . 

MgO 

Alkalies  .... 
H20    ...... 

99.8 

99.9 

99.71 

100.71 

99.98 

RATIONAL  ANALYSES 


Clay  substance 

63.8 

100.0 

84.12 

48.24 

33.57 

Quartz     .... 

•35.5 

0.0 

6.55 

49.72 

41.10 

Felspar    .... 

0.7 

0.0 

9.04 

2.75 

'  25.31 

100.0 

100.0 

99.71 

100.71 

99.98 

All  clays  have  a  peculiar  and  characteristic  odor  when  breathed 
upon  or  wet. 

The  preparation  of  clay  for  the  potter  is  simple.  It  is  mined, 
and  allowed  to  weather  for  several  months,  which  increases  its  plas- 
ticity by  promoting  hydration.  This  is  probably  aided  by  certain 


*  Lehrbuch  der  technischen  Chemie.     5te-  Auf.  H.  Ost,  262. 
t  Chemistry  of  Pottery.     K.  Langenbeck,  10,  111,  165. 


CERAMIC   INDUSTRIES  215 

enzymes,  of  bacterial  origin  in  some  cases.  Fine  clays  to  be  used  for 
the  better  grades  of  ware  are  then  thoroughly  "  slipped  "  with  water 
in  a  "  blunger  "  (a  vat  with  mechanical  stirrers),  and  thus  levigated. 
The  coarse  particles  of  quartz,  mica,  and  undecomposed  felspar  are 
separated,  and  only  the  clay  substance,  with  a  little  finely  divided 
quartz,  remains  in  suspension.  The  fine  mud,  called  "  slip/'  obtained 
by  settling  the  wash  waters,  is  pressed  in  cloth  bags  or  it  is  filter- 
pressed.  It  is  then  ready  for  use. 

Ceramics  comprise  two  general  divisions :  (a)  articles  having  a 
non-porous  body,  and  (6)  articles  having  a  porous  body.  Non-porous 
ware  is  hard,  impervious  to  liquids  and  gases,  and  has  a  semi-vitrified 
appearance  on  the  fractured  surface.  It  is  burned  at  a  very  high 
temperature,  and  is  chiefly  made  from  kaolin,  with  just  enough 
plastic  material  to  enable  the  workman  to  form  the  desired  article. 
This  division  includes  porcelain  and  stoneware.  Porous  ware  is  less 
dense,  has  an  earthy  appearance  on  the  fractured  surface,  and  per- 
mits the  passage  of  gases  and  liquids  through  its  pores.  It  is  made 
from  plastic  clays,  and  burned  at  a  low  or  moderate  temperature. 
It  comprises  bricks,  terra  cotta,  common  crockery,  and  some  kinds 
of  stoneware. 

There  are  two  kinds  of  porcelain,  the  hard  and  the  soft,  or 
"  fritted."  Both  are  harder  than  glass,  and  very  resistive  to  chem- 
ical action. 

Hard  porcelain  softens  only  at  the  highest  attainable  tempera- 
ture, and,  when  burned,  forms  a  perfectly  homogeneous  mass,  which 
is  translucent.  The  body  is  composed  of  kaolin,  quartz,  and  felspar, 
in  definite  proportions.  It  is  glazed  with  pure  felspar,  or  a  mixture 
of  quartz  and  felspar,  with  sufficient  lime  to  form  a  difficultly  fusible 
glass.  This  glaze,  which  must  have  the  same  coefficient  of  expan- 
sion as  the  body,  is  very  perfectly  welded  on  to  the  body,  by  a  second 
burning  at  a  high  temperature ;  and  no  distinct  line  of  demarcation 
between  the  body  and  the  glaze  can  be  seen  on  a  fractured  surface. 
Berlin,  Sevres  and  Meissen  ware  are  examples. 

Soft  porcelain  consists  of  a  kaolin  body,  with  ball-clay,  bone-ash, 
and  felspathic  materials  added.  This  is  burned  at  a  high  tempera- 
ture, and  glazed  with  a  lead-boric-acid  glass,  which  is  fused  on  to  its 
surface  by  a  second  much  lower  heating.  The  glaze  does  not  pene- 
trate so  perfectly,  but  forms  a  more  superficial  layer  than  is  the  case 
with  hard  porcelain.  English  china,  stone  ware,  and  Parian  ware  are 
soft  porcelain. 

In  preparing  the  clay  for  porcelains,  the  powdered  materials  are 


216  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

thoroughly  mixed,  wet,  and  the  "  slip  "  kneaded  and  allowed  to  age 
for  several  months.  The  articles  are  formed  on  the  potter's  wheel, 
a  horizontal  revolving  table,  driven  by  foot  or  machine  power.  Some- 
times the  slip  is  cast  in  porous  moulds  of  gypsum  or  burned  clay, 
which  absorb  the  water,  leaving  the  mud  on  the  face  of  the  mould. 
Or  the  partly  dried  mud  is  pressed  in  moulds  to  form  one  surface 
of  the  article,  the  other  being  completed  on  the  wheel,  as  is  the  case 
with  dishes  and  plates.  The  articles  are  very  slowly  dried  at  atmos- 
pheric temperature,  and  then  burned  at  a  low  red  heat,  to  give  them 
sufficient  coherence  to  permit  of  glazing. 

The  finely  powdered  glaze  mixture  is  sthred  up  with  water  to 
form  a  cream,  into  which  the  articles  are  dipped  and  at  once  with- 
drawn. A  layer  of  the  glaze  adheres  to  the  surface,  and,  after  dry- 
ing, the  article  is  ready  for  the  second  or  glaze  burning.  In  order 
to  protect  them  from  direct  contact  with  the  fire  in  the  kiln,  they 
are  enclosed  in  fire-clay  boxes,  called  "  saggers."  These  are  piled 
in  the  kiln  in  columns  or  "  bungs,"  extending  from  the  bottom  to 
the  top.  In  order  to  allow  sufficient  freedom  for  shrinkage,  the 
porcelain  is  supported  on  a  "  cockspur,"  a  small  tripod  of  fire-clay. 
The  contraction  of  porcelain  on  burning  is  nearly  13  per  cent  of  its 
original  volume.  After  burning,  the  ware  is  sorted ;  much  is  lost 
owing  to  warping,  to  bubbles  in  the  glaze,  and  to  discolorations  result- 
ing from  smoke  and  from  iron  oxide  in  the  material. 

The  body  of  all  ware  to  be  glazed  is  called  "  biscuit  "  after  the 
first  firing ;  that  of  soft  porcelain  which  has  been  hard  fired  is  called 
"  Parian."  Both  are  used  for  statuettes,  medallions,  and  reliefs. 

Stoneware,  which  is  also  a  non-porous  body,  is  made  from  refrac- 
tory material,  and  burned  at  high  temperatures.  But  the  color 
of  the  resulting  ware  may  range  from  white  and  gray  to  yellow  and 
brown.  It  is  not  attacked  by  chemicals,  and  withstands  tempera- 
ture changes  fairly  well.  The  finest  quality  is  the  well-known 
"  Wedgwood  "  ware,  which  comes  in  various  colors,  and  is  usually 
not  glazed.  The  gray  stoneware,  decorated  with  blue,  so  much 
used  for  drinking-mugs  and  ornamental  vases,  is  also  of  this  group. 
Yellow  and  brown  varieties  are  much  used  for  mineral  water-bottles, 
bombonnes,  condenser  tubes,  and  glazed  pipes  in  chemical  factories. 
The  clays  are  less  pure  than  those  for  porcelain,  and  the  ware  is  burned 
without  saggers,  at  a  very  high  temperature.  A  "  salt  glaze  "  is 
used,  to  form  which  common  salt  is  thrown  into  the  kiln,  and,  -  vol- 
atilizing, combines  with  the  silicates  of  the  stoneware  to  form  double 
silicates  of  soda  and  alumina  on  the  surface  of  the  ware ;  or  the 


CERAMIC  INDUSTRIES  217 

articles  are  "  slip  glazed  "  by  applying  an  easily  fusible  clay  as     slip/* 
before  firing. 

The  kilns  for  potters'  use  are  of  several  kinds.  A  common  form 
is  the  up-draught  kiln,  in  which  the  flame  enters  at  the  bottom  and 
passes  up  between  the  "  bungs,"  and  out  at  the  chimney  above. 
A  better  type  is  the  down-draught  kiln,  which  is  sometimes  built 
in  two  stories.  The  lower  story  is  filled  with  the  ware  to  be  fired 
at  the  highest  temperature,  and  the  upper  with  that  to  be  burned 
at  a  less  heat.  The  flame  from  the  grate  passes  up  through  flues 
in  the  kiln  walls,  and  enters  the  lower  chamber  near  the  top.  It 
then  goes  down  between  the  bungs,  and,  through  openings  in  the 
floor,  into  other  flues  in  the  walls,  around  the  upper  chamber,  and 
thence  to  the  chimney.  This  kiln  is  economical  of  fuel,  affords 
very  even  temperature  in  the  lower  chamber,  and  utilizes  the  heat 
which  is  lost  in  the  up-draught  kiln.  A  special  form  of  Hoffmann's 
ring  furnace  (p.  185)  is  also  employed  for  pottery  and  brick  burning. 
In  a  new  form  of  kiln,  the  bungs  are  arranged  on  cars,  which  travel 
slowly  through  a  long  gallery,  towards  the  firing  chamber.  The 
waste  heat  from  the  hot  chamber  enters  the  gallery  at  the  end  next 
the  firing  room,  and,  coming  in  contact  with  the  pottery,  heats  it  to 
a  temperature  corresponding  to  its  distance  from  the  inlet  flue.  The 
cars  move  through  the  furnace  into  a  second  long  gallery,  where  the 
heat  from  the  saggers  warms  the  air  which  is  passing  into  the  fur- 
nace, thus  utilizing  the  waste  heat.  The  firing  compartment  usually 
contains  two  loaded  cars ;  and  the  grate  being  at  one  end  of  the  fir- 
ing room,  the  pottery  in  each  car  gets  a  preliminary  firing  before  it 
reaches  the  hottest  part  of  the  kiln.  As  soon  as  one  car  is  fired,  it  is 
pushed  into  the  cooling  gallery,  the  rear  car  is  moved  into  the  hottest 
compartment  of  the  kiln,  and  another  is  introduced  from  the  pre- 
liminary warming  gallery.  This  furnace  is  economical  of  fuel,  gives 
an  even  temperature,  and  the  time  of  firing  being  greatly  reduced, 
there  is  less  loss  of  saggers  and  pottery. 

Porous  ware,  the  second  division  of  ceramics,  is  manufactured 
extensively  in  all  countries.  The  finest  grade  is  "  faience."  This  is 
made  from  a  white  clay,  which  is  washed,  levigated,  and  aged,  much 
as  for  porcelain.  The  better  grades  are  burned  in  saggers  at  a  high 
temperature,  and  glazed  with  a  transparent  lead  glaze  at  a  much 
lower  heat.  Majolica  also  belongs  to  this  group,  being  a  colored  porous 
body,  covered  with  a  non-transparent  glaze. 

Between  faience  and  common  pottery  no  sharp  line  can  be  drawn. 


218  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

The  color  ranges  through  cream,  yellow,  brown,  and  red,  and  the 
body  consists  of  more  or  less  fusible  clay,  with  a  still  more  fusible 
lead  glaze,  which  is  often  colored  with  metallic  oxides.  The  clays 
for  common  pottery  are  generally  "  slipped,"  and  strained  through 
fine  sieves  to  remove  stones  and  coarse  grains.  The  articles  are 
fashioned  on  the  potter's  wheel  and  are  air  dried.  They  are  then 
dipped  in  a  glaze  made  of  litharge  and  clay,  shaken  to  a  cream  with 
water.  Or  the  dry  mixture  is  powdered  over  the  surface  from  a  pepper 
box.  Or  they  are  given  a  "  salt  "  glaze  as  before  described.  They 
are  burned  without  saggers,  and  at  a  temperature  only  sufficient  to 
fuse  the  glaze. 

Tiles  are  a  special  form  of  pottery,  consisting  of  flat,  thin  plates, 
much  used  for  floors,  panels,  and  architectural  purposes.  They  are 
finer  ware  than  common  brick,  and  more  care  is  taken  in  the  prepa- 
ration of  the  body  and  in  the  burning.  There  are  three  classes, 
vitrified,  encaustic,  and  glazed. 

Vitrified  tiles  consist  of  single  pieces,  made  by  one  burning  at  a 
very  high  temperature,  so  that  the  entire  body  of  the  tile  is  semi- 
fused.  They  are  not  glazed,  and  are  a  form  of  stoneware  much 
used  for  pavements  and  floors,  because  of  their  hardness. 

Encaustic  tiles  are  made  from  two  or  more  clays,  generally  of 
different  colors.  A  facing  of  fine  clay  may  be  put  on  a  back  of  com- 
moner quality.  The  ornamental  design  is  made  by  inlaying  the 
face  with  other  clays,  which  burn  to  different  colors.  All  the  mate- 
rials must  have  the  same  coefficient  of  expansion,  so  that  no  cracks 
form  between  the  different  parts  of  the  design.  These  tiles  are 
generally  used  for  ornamental  purposes,  and  are  often  covered  with 
a  transparent  glaze,  necessitating  two  burnings. 

Glazed  tiles  are  made  with  a  body  (which  may  consist  of  more 
than  one  clay)  of  uniform  color,  covered  with  a  transparent  glaze, 
colored  or  not,  according  to  the  effect  desired. 

The  dry  clay,  flint,  felspar,  Cornish  stone,*  "  grog,"  and  other 
materials  in  the  mixture  for  the  body  of  the  tile,  are  put  into  a  re- 
volving drum  (Alsing  mill),  along  with  a  number  of  round  flint  stones. 
After  five  or  six  hours'  grinding,  the  mixture  is  complete.  The  dry 
powder  is  then  sifted  through  a  fine  sieve.  There  are  two  methods 
of  forming  the  tile,  the  "  dust  body  "  and  the  "  wet  body  "  process. 
In  the  dust  body  method  the  sifted  clay  mixture  is  dampened  by  spread- 

*  Cornish  stone  is  partly  weathered  felspar,  being  thus  a  mixture  of  kaolin, 
felspar,  quartz,  and  mica.  It  is  mined  in  England,  and  much  used  as  a  flux  and 
fusible  ingredient  in  porcelain  and  tiles. 


CERAMIC  INDUSTRIES  219 

ing  on  a  wet  plaster  of  Paris  floor.  It  is  shovelled  over  and  allowed 
to  remain  on  the  floor  until  the  particles  of  clay  will  just  stick  to- 
gether when  pressed  in  the  hand.  It  is  then  filled  into  a  metallic 
mould  which  contains  the  intaglio  for  relief  designs ;  it  is  then  heavily 
pressed  in  a  screw  or  hydraulic  press.  This  compacts  the  clay, 
and  gives  sufficient  coherence,  so  that  the  green  tile  may  be  removed. 
It  is  exceedingly  brittle,  and  must  be  handled  very  carefully.  It 
is  well  dried  in  a  room  where  there  is  a  good  circulation  of  air.  To 
prevent  discoloration,  tiles  are  burned  in  saggers  in  which  they  are 
loosely  packed  in  quartz  sand  to  prevent  their  twisting  and  bending, 
since  they  become  very  soft  at  high  temperatures. 

In  the  wet  body  process  the  slip  is  moulded  in  plaster  of  Paris 
moulds.  After  standing  half  an  hour,  or  more,  until  the  water  has 
all  been  absorbed  by  the  plaster,  the  clay  cast  is  removed,  dried 
slowly,  and  burned  as  in  the  case  of  dust  body  tiles. 

Glazes,  both  for  hollow  ware  of  all  sorts  and  for  tiles,  are  of  three 
kinds,  engobe,  enamel,  and  transparent. 

The  engobe  is  a  fusible  clay,  felspar,  or  alkali,  applied  in  a  very 
thin  coating.  It  forms  a  thin  glaze,  usually  opaque,  which  is  intended 
to  support  a  second  thicker  glaze  or  enamel. 

Enamels  are  usually  transparent  glazes,  holding  in  suspension 
opaque  substances  such  as  oxide  of  tin.  A  mixture  of  litharge  and 
tin  oxide  ("  ashes  of  tin  ")  is  very  often  used  for  enamel. 

Transparent  glazes  are  practically  lead  or  lime  glass.  This  is 
sometimes,  though  rarely,  used  as  "  raw  glaze,"  i.e.  the  materials  are 
ground  fine,  mixed,  and  applied  to  the  ware  as  a  cream  with  water. 
This  is  difficult  to  do,  owing  to  the  great  density  of  the  litharge, 
which  settles  out  of  the  cream,  on  standing  even  a  short  time.  To 
avoid  this  separation  and  loss,  and  to  allow  the  use  of  substances 
soluble  in  water,  e.g.  borax,  soda-ash,  or  boric  acid,  the  glaze  is  gen- 
erally "  fritted  "  or  semi-fused,  before  making  it  into  a  cream  with 
water.  The  powdered  and  thoroughly  mixed  material,  together 
with  coloring  substances  if  desired,  is  heated  in  a  sagger  until  it 
forms  a  coherent  mass,  but  is  not  completely  fused.  The  frit  is  then 
powdered  in  a  ball  mill.  Fritted  glaze  is  much  more  uniform  than 
raw,  and  there  is  no  tendency  to  segregation  of  its  components. 

In  all  kinds  of  glazed  ware,  it  is  very  essential  that  the  glaze 
and  body  shall  have  the  same  coefficient  of  expansion,  or  cracking 
of  the  glaze  is  liable  to  occur.  This  is  called  "  crazing,"  and  is 
caused  by  the  glaze  contracting  too  much  in  cooling ;  the  scaling  off 


220  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

of  glaze  and  attached  body  from  high  points  of  the  tile,  called  "  shiv- 
ering," is  caused  by  insufficient  contraction  of  the  glaze.  To  pre- 
vent these  defects  the  glaze  or  the  body  is  so  modified  that  the  co- 
efficients of  expansion  are  the  same.  The  exact  adjustment  of  this 
factor  is  a  matter  of  experience.  The  usual  methods  employed 
are,  —  to  render  the  body  less  plastic  by  the  addition  of  lean  clay, 
grog,  or  quartz,  thus  increasing  the  silica,  which  increases  the  expan- 
sion of  the  body ;  or  to  modify  the  glaze  by  the  addition  of  silica 
or  boric  acid  for  greater  expansion,  or  of  lime,  lead,  or  alkali,  to 
increase  the  contraction.  Boric  acid,  lead,  and  alkali  make  it  more 
fusible,  and  the  temperature  of  the  intended  burning  must  be  kept 
in  mind  when  adding  these  ingredients.  Boric  acid  and  lead  also 
increase  the  brilliancy  of  the  glaze.  The  addition  of  certain  color- 
ing matter  to  glazes  also  increases  the  tendency  to  craze.  Alumina 
is  essential  in  a  glaze  to  prevent  devitrification  during  the  burning. 

Terra  cotta  has  a  soft  porous  body,  and  is  not  glazed.  Its  color 
depends  on  the  character  of  the  clay.  Generally  a  highly  ferruginous 
clay  is  used,  which  has  a  deep  red  color  when  burned.  It  is  exten- 
sively employed  for  architectural  effects  and  for  tiles. 

Bricks  are  probably  the  most  important  of  the  porous  ware. 
They  are  made  from  common  clay,  which  usually  contains  consider- 
able impurity,  lime  and  iron  oxide  often  being  present  in  large  quan- 
tities. The  preparation  of  the  clay  is  a  simpler  process  than  for 
pottery.  After  digging  it  is  usually  weathered  for  several  months, 
and  then  screened,  to  remove  pebbles  of  quartz  or  limestone.* 
It  is  then  "  pugged  "  or  "  tempered,"  by  mixing  thoroughly  with 
water  and  tlie  ingredients  to  make  the  desired  "  body  " ;  in  the 
case  of  a  fat  clay,  these  are  sand,  grog,  or  other  clays.  This  is  done 
in  a  "pug  mill,"  a  tank  containing  a  revolving  stirring  apparatus, 
which  pushes  the  mass  out  at  the  bottom  in  proper  condition  to  be 
used  at  once.  The  paste  is  moulded  into  bricks,  by  hand  for  the  finer 
sort,  and  by  machinery  for  the  common  grades.  The  latter  are  apt  to 
be  uneven  and  rough.  The  moulded  bricks  are  dried  in  the  air,  usually 
in  the  yard,  under  a  light  shed.  They  are  turned  over  frequently 
during  the  drying,  which  must  not  be  too  rapid,  lest  the  bricks  crack. 

The  firing  is  done  in  kilns  which  may  be  built  of  the  air-dried 
brick,  numerous  channels  being  left  for  the  passage  of  flame  and  hot 
gases.  This  mode  of  burning  results  in  several  grades  of  brick, 

*  Limestone  pebbles  are  very  injurious,  since  the  burning  converts  them  into 
lumps  of  lime  within  the  brick,  and  when  the  latter  is  wet  or  exposed  to  weather  the 
lime  is  hydrated,  and,  expanding,  disintegrates  the  brick. 


CERAMIC  INDUSTRIES  221 

owing  to  the  unequal  distribution  of  heat.  Or  closed  kilns,  such  as 
the  Hoffmann  ring  furnace  (p.  185),  may  be  used.  This  gives  a  more 
even  product  than  the  open  kiln. 

In  this  country  wood  and  coal  are  used  for  fuel,  but  gas  is  fre- 
quently employed  abroad.  The  temperature  in  the  kiln  for  common 
brick  seldom  goes  higher  than  1000°  C. ;  but  for  hard,  paving  brick 
it  may  be  raised  to  1200°  or  1300°  C.,  producing  incipient  fusing. 
The  heat  also  affects  the  color  of  some  bricks ;  high  temperature 
yields  a  dark  red,  gray,  or  bluish  black,  according  to  the  amount  of 
ferroso-ferric  oxide  (Fe3O4)  formed.  Clays  containing  much  lime 
yield  yellow  or  cream-colored  brick,  if  iron  is  also  present. 

Common  brick  will  fuse  if  exposed  to  high  heat,  and  are  not  suit- 
able for  lining  fireplaces,  furnaces,  or  ovens. 

Fire-brick  are  made  from  fire-clay,  with  the  addition  of  a  large 
amount  of  "  grog  "  or  silica.  These  must  resist  great  heat,  and  not 
shrink  nor  warp.  The  clay  is  prepared  similarly  to  that  for  common 
brick,  but  more  care  is  taken  in  the  mixing.  The  bricks  are  also 
heavily  pressed  to  increase  the  density.  The  burning  is  at  the  highest 
temperature  possible,  so  that  no  shrinkage  will  occur  later  when  the 
bricks  are  in  use.  They  are  brittle,  and  must  be  supported  by  a 
backing  of  common  hard  brick. 

Bricks,  the  body  of  which  are  magnesia,  chromite,  silica,  etc., 
mixed  with  just  enough  plastic  clay  to  make  them  workable  and  to 
cement  the  grains  of  the  body  when  burned,  are  largely  employed  in 
chemical  furnaces  to  withstand  high  temperature  corrosion  of  various 
types  of  charge. 

REFERENCES 

Handbuch  der  gesammten  Thonwaarenindustrie.  Bruno  Kerl,  Braun- 
schweig, 1879. 

Traite  des  Arts  ceramiques  ou  des  Poteries.     Alexandre  Brongniart. 

Lecons  de  ceramique.     A.  Salvetat. 

La  Faience.     Th.  Deck. 

Report  on  the  clay  deposits  of  Woodbridge,  South  Amboy,  etc.  Public 
Documents  of  New  Jersey. 

A  Practical  Treatise  on  the  Manufacture  of  Bricks.     C.  T.  Davis. 

Pottery  and  Porcelain  of  the  United  States.     E.  A.  Barber. 

Die  Steingut-Fabrikation.     Gustav  Steinbrecht,  Leipzig,  1891. 

Ziegel-Fabrikation  der  Gegenwart.      Herman  Zwick,  Leipzig,  1894. 

Seger's  gesammelte  Schriften.     H.  Hecht  und  E.  Cramer,  Berlin,  1896. 

The  Chemistry  of  Pottery.     Karl  Langenbeck,  Easton,  Penn.,  1895. 

Clays.     Heinrich  Ries,  New  York,  1906.     (Wiley  &  Sons.) 

Clay  and  Pottery  Industries.    J.  W.  Mellor,  London,  1914. 

The  Silicates  in  Chemistry.  W.  Asch  and  D.  Asch.  Trans,  by  A.  B. 
Searle,  New  York,  1914. 


PIGMENTS 

Pigments  are  mineral  or  organic  bodies,  usually  insoluble  in 
water,  oils,  and  other  neutral  solvents,  and  are  used  to  impart  color 
to  a  body,  either  by  mechanical  adhesion  to  its  surface  or  by  ad- 
mixture with  its  substance.  In  most  cases  there  is  no  chemical 
combination  between  the  pigment  and  the  body  it  colors. 

The  color  of  a  pigment  depends  upon  the  amount  and  kind  of 
light  which  it  reflects.  It  is  essential  that  the  pigment  be  opaque 
(possess  large  capacity  to  absorb  transmitted  light)  in  order  that 
it  may  have  a  good  "  covering  power  "  or  "  body  " ;  i.e.  it  should 
entirely  conceal  the  surface  to  which  it  is  applied.  Many  pig- 
ments are  prepared  by  chemical  precipitation,  but  some  of  the 
most  important  are  not. 

Pigments  form  the  basis  of  paint,  which  consists  of  a  mixture  of 
a  pigment  with  some  drying  oil,  or  with  water  containing  gum  or 
size.  It  is  used  for  decorative  and  protective  purposes ;  if  used  for 
outside  work,  the  pigment  should  be  insoluble  in  water. 

The  durability  of  a  paint  depends  on  the  chemical  stability  of 
the  mixture  of  pigments  and  vehicle  composing  the  film,  and  on  its 
mechanical  strength,  resistance,  and  impermeability.  These  proper- 
ties are  best  secured  by  using  a  mixture  of  relatively  coarse  and  fine 
pigments ;  the  first  form  a  skeleton  of  large  particles,  giving  strength 
and  rigidity,  and  the  latter  render  the  mass  impermeable  by  filling 
the  voids  between  the  coarse  particles.  Thus  while  coarse  pigments 
(barytes,  silica,  chalk,  etc.)  are  almost  valueless  alone,  their  addition, 
in  quantities  up  to  10  per  cent,  greatly  increases  the  wearing 
qualities  of  paints  containing  fine  pigments  (white  lead,  zinc  oxide, 
etc.).  Furthermore  mixtures  of  fine  pigments, — which  differ  from 
each  other  in  size  of  particle,  —  are  better  than  the  pure  pigments 
alone.  This  has  been  established  in  the  case  of  white  pigments ; 
with  colored  pigments,  chemical  changes  in  the  pigment,  vehicle,  or 
both,  frequently  complicate  the  matter. 

WHITE  PIGMENTS 

White  lead  is  the  most  important  of  all  pigments,  and  is  a 
very  old  one,  the  native  carbonate,  cerussite,  having  been  used  by 
the  Romans.  But  as  this  mineral  is  restricted  in  its  distribution 

222 


PIGMENTS  223 

the  artificial  product  was  in  time  brought  into  use.  The  so-called 
Dutch  process  of  making  white  lead  is  the  oldest  known,  reference 
being  made  to  it  as  far  back  as  1622.  With  a  few  modifications,  it 
is  still  in  use,  and  yields  a  product  which  for  many  purposes  is 
preferred  by  painters  to  the  lead  manufactured  by  the  numerous 
newer  processes.  It  usually  has  more  covering  power  and  a  better 
color. 

White  lead  is  a  basic  lead  carbonate,  and  analyses  of  the  best 
samples  give  as  constitutional  formula  about  2  PbCOs,  Pb(OH)2,  in 
which  there  are  two  molecules  of  PbCOs  to  one  of  hydroxide.  This 
appears  to  be  the  best  ratio.  But  the  white  lead  of  trade  varies 
a  good  deal,  according  to  the  method  and  conditions  of  making. 
In  some  cases  it  is  nearly  pure  PbCOs,  and  in  others  the  propor- 
tion of  carbonate  to  hydroxide  is  as  high  as  three  to  one,  or  more. 
But  some  hydroxide  is  necessary  in  order  that  the  white  lead  may 
have  a  good  covering  power.  Then,  too,  the  hydroxide  is  sup- 
posed to  combine  with  the  oil  chemically  to  form  a  "  lead  soap," 
which  perhaps  dissolves  in  the  'excess  of  oil  to  form  a  kind  of 
varnish. 

There  are  three  general  methods  employed  in  white  lead  making, 
besides  numerous  patent  processes.  These  are :  — 

The  Dutch,  or  Stack  process. 

The  German,  or  Chamber  process. 

The  French,  or  Thenard's  process. 

The  Dutch  process  consists  in  exposing  sheet  lead  to  the  direct 
action  of  moisture,  acetic  acid  vapors,  and  carbon  dioxide.  The 
corrosion  is  effected  in  earthenware  pots  8  inches  in  depth  by  5  inches 
in  diameter,  glazed  inside,  and  made  in  the  form  of  crucibles,  each 
containing  a  shelf.  On  this  shelf  is  a  spiral  or  "  buckle  "  of  thin 
sheet  lead,  made  by  rolling  up  a  sheet  of  lead  2  feet  long  by  4  inches 
wide;  or  cast  buckles  of  various  forms  to  expose  a  large  surface  to 
the  fumes,  may  be  used.  In  the  lower  compartment  is  dilute  acetic 
acid,  containing  from  3  to  5  per  cent  C2H4O2.  A  large  number  of 
these  pots  so  charged  are  packed  in  a  shed  or  brick  building,  having  an 
opening  on  one  side  reaching  from  the  ground  nearly  to  the  roof.  A 
layer  of  ashes  is  spread  over  the  floor  first,  and  then  a  layer  4  or  5 
feet  thick  of  spent  tan  bark  which  is  moist  and  ready  to  ferment. 
This  is  well  packed  down,  and  the  pots  placed  side  by  side  upon  it 
until  the  whole  space  is  filled,  excepting  about  6  inches  next  the  walls, 
which  is  solidly  filled  in  with  the  tan.  More  lead  buckles  or  lead  grat- 
ings are  placed  across  the  tops  of  the  pots,  so  as  to  form  a  layer  of 


224  OUTLINES    OF    INDUSTRIAL   CHEMISTRY 

metallic  lead  about  4  inches  deep.  Then  about  6  inches  above  this, 
and  supported  by  timbers  or  blocks,  is  a  board  floor  upon  which  the 
next  layer  of  tan,  about  one  foot  deep,  is  placed,  and  the  pots  upon  it 
as  above  described.  The  doorway  is  boarded  up  as  the  filling  continues, 
and  the  "  stack,"  as  the  alternate  layers  of  pots  and  tan  are  called, 
is  carried  to  within  a  few  feet  of  the  top  of  the  shed.  For  a  stack 
20  by  12  by  18  feet  in  size,  40  or  50  tons  of  lead  are  required,  about 
3  tons  of  lead  and  200  gallons  of  acid  being  used  in  each  layer  of  pots. 
Very  soon  after  packing  an  active  fermentation  of  the  tan  sets  in, 
the  temperature  rising  to  about  55°-60°  C.  This  heat  is  sufficient 
to  vaporize  the  acetic  acid  and  water,  and  these  vapors  attack  the 
metallic  lead,  forming  a  basic  lead  acetate.  Great  quantities  of 
carbon  dioxide  are  liberated  during  the  fermentation,  and  this  decom- 
poses the  lead  acetate,  forming  basic  lead  carbonate,  or  white  lead. 
The  reactions,  aside  from  those  of  fermentation,  may  be  represented 
by  the  following  :  — 

1)  Pb  +  2  C2H4O2  =  H2  +  Pb(C2H3O2)2.     (Normal  lead  acetate.) 

2)  3  Pb(C2H3O2)2  +  2  H2O  =  2  Pb(C2H3O2)2,  Pb(OH)2  +  2  C2H4O2. 

3)  2  Pb(C2H3O2)2,  Pb(OH)2  +  2  CO2  +  2  H2O  = 

2  PbCO3,  Pb(OH)2  +  4  C2H402. 

Some  authorities  consider  the  reactions  to  be  as  follows :  — 

a)  Pb  +  H20  +  O  =  Pb(OH)2. 

b)  Pb(OH)2  +  2  C2H4O2  =  Pb(C2H302)2  +  2  H2O. 

c)  Pb(C2H3O2)2  +  2  Pb(OH)2  =  Pb(C2H3O2)2, 2  Pb(OH)2.    (Basic  lead 

acetate.) 

d)  3  SPb(C2H302)2,  2  Pb(OH)2(  +  4  CO2  = 

3  Pb(C2H3O2)2  +  2  fPb(OH)2,  2  PbCO3J  +  4  H2O. 

Thus  the  acetic  acid,  or  the  neutral  lead  acetate,  is  regenerated, 
and  attacks  more  of  the  metallic  lead,  and  the  process  repeats  itself. 
But  the  action  is  very  slow,  the  time  usually  allowed  for  a  stack  to 
work  being  about  three  months.  If  horse  dung  is  used  instead  of 
the  tan  bark,  as  it  formerly  was,  the  process  is  quicker,  taking  about 
two  months;  but  the  sulphur  compounds  formed  in  this  fermenta- 
tion darken  the  white  lead  more  or  less. 

Usually  the  metallic  lead  is  nearly  all  corroded  and  converted 
into  white  lead,  but  never  completely,  and  the  product  is  seldom 
equally  good  in  all  parts  of  the  stack.  Well-corroded  buckles  retain 


PIGMENTS  225 

their  shape,  although  they  become  rather  more  bulky  and  of  a  gray- 
ish white  color,  and  have  a  firm,  porcelain-like  structure.  When  soft 
and  powdery,  the  product  is  not  so  satisfactory.  The  "  corrosions  "  are 
taken  to  the  grinding  room  and  put  through  rolls,  which  break  them 
into  fine  powder;  the  uncorroded  lead  is  rolled  out  into  plates  and 
scales,  which  are  retained  on  the  sieves  when  the  mass  is  screened. 
The  white  lead  passes  through,  and  is  reduced  to  a  fine  pulp  by  wet 
grinding  in  an  edgestone  or  horizontal  mill,  and  then  levigated; 
salt  is  often  added  to  the  water  to  accelerate  the  sedimentation. 
The  coarser  particles  from  the  first  settling  tanks  are  returned  to  the 
mills  and  reground.  In  the  final  settling  tanks  is  left  a  heavy  white 
mud,  which  may  be  dried  in  steam-jacketed  copper  pans.  Usually 
the  wet  mud  is  mixed  with  about  9  per  cent  of  raw  linseed  oil,  in  me- 
chanical mixers  of  the  helical  screw  type.  The  oil  combines  mechani- 
cally with  the  pigment  and  the  mixture  settles,  while  the  water,  now 
almost  free  from  lead,  is  drawn  off  from  above.  The  paste  of  lead  in 
'  oil  contains  so  little  water  that  it  is  not  further  dried  as  a  rule,  but 
is  packed  directly  for  shipment.  This  method  avoids  the  dust  pro- 
duced in  handling  the  dry  pigment. 

The  white  lead  comes  in  trade  either  dry  or  mixed  with  about  9 
per  cent  of  raw  linseed  oil.  If  it  is  slightly  yellow,  due  to  stains  from 
the  colored  liquids  in  the  tan,  or  to  tarry  matters  in  the  acetic  acid, 
or  to  overheating  in  the  drying,  a  little  indigo  or  Prussian  blue  may 
be  added  to  neutralize  this.  One  ton  of  the  metallic  lead  yields  about 
1 J  tons  of  the  white  lead ;  but  the  process  is  always  somewhat  un- 
certain both  as  to  quantity  and  quality  of  the  product.  Sometimes 
very  little  corrosion  takes  place,  and  this  may  vary  in  different  parts 
of  the  stack.  The  process  is  slow,  a  large  plant  is  required,  and  the 
capital  invested  lies  idle;  hence  the  price  of  white  lead  is  somewhat 
higher  than  the  simplicity  of  the  method  would  at  first  glance  appear 
to  warrant. 

To  obtain  good  results  by  the  Dutch  method  the  lead  must  be 
very  pure.  If  any  silver,  copper,  or  iron  is  present,  the  color  of  the 
white  lead  will  be  damaged.  Antimony,  arsenic,  bismuth,  and  zinc 
are  said  to  retard  the  corrosion  very  much. 

The  German,  or  chamber,  process  is  an  artificial  method  of  pro- 
ducing about  the  same  conditions  as  prevail  inside  the  stack  in  the 
Dutch  method.  The  reactions  are  the  same.  Lead  plates  are  hung 
or  arranged  on  shelves  in  a  closed  chamber,  provided  with  a  door  and 
window  for  filling  and  for  watching  the  process.  Dishes  of  acetic 
acid  are  placed  on  the  floor,  or  acetic  acid  vapor  is  introduced  from 

Q 


226  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

stills  outside,  the  room  is  heated  by  steam  to  about  38°  C.,  and  carbon 
dioxide  is  introduced.  This  is  much  more  rapid  than  the  Dutch 
method,  usually  requiring  about  five  weeks,  but  the  quality  of  the 
product  is  not  so  satisfactory.  There  are  difficulties  to  contend  with 
in  the  rate  of  flow  of  the  acid  vapors,  steam,  and  carbon  dioxide,  and 
in  the  regulation  of  the  temperature.  Too  much  acetic  acid  vapor 
causes  loss  of  lead  as  neutral  acetate ;  too  much  carbon  dioxide  pre- 
cipitates normal  lead  carbonate;  too  little  acetic  acid  or  too  high 
a  temperature,  with  excess  of  water  vapor,  may  form  lead  oxide, 
which,  being  yellow,  injures  the  product.  Many  modifications  of 
this  process  have  been  invented,  and  some  of  them  are  worked  more 
or  less  successfully.  In  one  form,  the  chamber  is  fitted  with  tracks, 
on  which  cars  are  run,  carrying  the  sheet  lead  in  frames.  A  car 
can  be  run  out,  and  another  introduced,  without  much  loss  of  time 
or  cooling  of  the  chamber.  The  white  lead  made  by  this  method  is 
ground  and  levigated  as  already  described. 

Carter's  process  is  much  used  and  produces  white  lead  of  good 
quality.  Atomized  lead,  made  by  blowing  a  jet  of  superheated  steam 
against  a  fine  stream  of  melted  lead,  is  put,  in  two-ton  charges,  into 
rotary  wooden  cylinders,  6  feet  in  diameter  by  10  feet  long;  dilute 
acetic  acid  is  sprayed  in,  and  carbon  dioxide  with  air  admitted  through 
the  centre  of  the  head,  while  the  barrel  revolves  slowly.  The  con- 
stant stirring  accelerates  the  process,  and  corrosion  is  complete  in 
about  15  days.  The  tumbling  of  the  mass  also  serves  to  pulverize 
the  white  lead.  The  carbon  dioxide  is  made  by  combustion  of  good 
coke  with  excess  of  air.  Coleman's  process  is  similar  but  the  carbon 
dioxide  is  used  under  pressure. 

The  French  process,  or  ThenarcTs  method,  depends  on  precipitation 
of  a  basic  lead  carbonate  from  a  solution  of  a  basic  salt  by  means  of 
carbon  dioxide.  The  solution  generally  used  is  a  basic  lead  acetate, 
prepared  by  boiling  litharge  with  neutral  acetate.  The  reactions 
are:  — 

1)  2  PbO  +  Pb(C2H3O2)2  +  2  H2O  =  Pb(C2H3O2)2,  2  Pb(OH)2. 

2)  3[Pb(C2H3O2)2  -  2  Pb(OH)2]  +  4  CO2  = 

3  Pb(C2H302)2  +  2 [2  PbCO3,  Pb(OH)2]  +  4  H2O. 

The  reactions  are  carried  out  in  the  apparatus  shown  in  Fig.  87.* 
The  litharge  is  mixed  with  the  solution  of  neutral  lead  acetate  in 
the  tank  (A),  which  is  heated  by  a  steam  pipe.  When  saturated, 
the  mixture  is  run  into  the  settling  tank  (B),  where  the  undissolved 

*  After  Hurst,  Painter's  Colours,  Oils  and  Varnishes. 


PIGMENTS 


227 


litharge  deposits.  The  clear  solution  of  basic  lead  acetate  is  then 
run  into  the  precipitating  vessel  (C),  where  it  is  treated  with  carbon 
dioxide,  introduced  through  the  pipes  (D,  D).  The  basic  lead  car- 
bonate falls  as  a  heavy  white  precipitate,  while  a  solution  of  neutral 
lead  acetate  remains.  After  settling,  the  solution  is  drawn  into  the 
tank  (E),  from  which  it  is  pumped  back  into  (A),  where,  after  add- 
ing a  small  amount  of  acetic  acid,  it  is  used  again.  The  white  lead 
is  collected  in  (F),  from  which  it  is  taken  to  be  filtered  and  washed. 
The  carbon  dioxide  used  must  be  pure  and  concentrated,  and  is  made 
by  heating  calcium  carbonate  with  coke,  in  a  special  furnace  (G). 
The  gas  is  passed  through  water  in  (H)  to  remove  impurities,  and 
then  goes  to  the  precipitating  vessel. 

The  precipitation  requires  from  10  to  14  hours  or  more,  varying, 
as  does  also  the  quality  of  the  product,  with  the  quantity  and  strength 


FIG.  87. 


of  the  solution  of  basic  acetate.  The  white  lead  separates  in  a  gran- 
ular or  crystalline  form,  and  is  washed,  ground,  and  dried,  as  in  the 
methods  already  described.  It  is  said  to  have  less  covering  power 
than  the  amorphous  powder  produced  by  the  Dutch  method. 

Many  chemical  processes  based  upon  the  precipitation  of  a  basic 
lead  carbonate  from  solutions  of  various  lead  salts,  have  been  pro- 
posed, such  as  Milner's  process,  the  Kremnitz  process,  and  cer- 
tain electrolytic  processes,  but  these  as  yet  have  not  developed 
industrially. 

Methods  depending  upon  the  precipitation  of  basic  lead  solutions 
with  sodium  carbonate  have  the  disadvantage  of  forming  crystalline 
product. 

Many  electrolytic  processes  have  been  proposed :  thus  in  modifi- 
cation of  the  chamber  process,  lead  is  placed  on  shelves,  covered 
with  carbon  or  tin  plates,  through  which  an  electric  current  passes. 


228  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

More  rapid  corrosion  of  the  lead  thus  charged,  by  the  carbon  dioxide 
and  acetic  acid  vapors,  with  formation  of  a  granular  product,  is 
claimed. 

It  has  been  proposed  to  make  a  precipitated  lead  hydroxide  by 
electrolysis  with  lead  anodes  and  inert  cathodes,  in  a  bath  of  sodium 
nitrate,  the  hydrate  being  then  treated  with  a  solution  of  sodium  bi- 
carbonate ;  but  this  method  of  corrosion  of  the  lead  is  expensive  and 
has  not  proved  a  success. 

A  general  method  for  the  electrolytic  production  of  insoluble 
salts  the  formulae  of  which  may  be  written  as  MA,  in  which  M  is  the 
metal  and  A  the  anion  of  the  salt,  is  to  employ  anodes  of  the  metal 
M  in  an  electrolyte  containing  two  soluble  salts,  NA  and  NB,  N  being 
a  suitable  metal,  usually  an  alkali,  and  B  an  anion  whose  salt  with 
M  is  soluble.  At  the  anode  the  salt  MB  is  formed  and  diffuses  out 
into  the  solution,  where  it  is  precipitated  by  double  decomposition 
with  NA.  The  precipitate  not  being  formed  on  the  anode  itself  is 
non-adherent  and  hence  does  not  interfere  with  the  electrolysis,  as 
would  otherwise  be  the  case.  A  specific  illustration  of  this  method 
is  the  Liickow  process.*  The  electrolyte,  composed  of  solutions  of 
80  parts  sodium  chlorate  and  20  parts  sodium  carbonate,  is  diluted 
to  such  a  degree  that  it  contains  1.5  per  cent  of  anhydrous  salts,  since 
dilute  liquors  yield  the  purest  product.  The  liquid  is  kept  slightly 
alkaline,  and  carbon  dioxide  is  passed  into  it  to  replace  the  carbonate 
precipitated  with  the  white  lead.  The  cathodes  of  crude  lead  and 
the  anodes  of  pure,  soft  lead,  each  having  an  area  of  20  to  30  sq.  dcm., 
are  placed  about  12  to  15  mm.  apart,  and  the  current  density  is  0.5 
ampere  per  sq.  dcm.  with  a  voltage  about  2.  The  voltage  varies 
somewhat  according  to  the  conductivity  of  the  electrolytes  and  the 
distance  between  the  pairs  of  electrodes. 

Owing  to  the  high  price  of  white  lead,  it  is  frequently  adulterated 
with  barytes  (BaSCy,  lead  sulphate,  lead  carbonate,  or  calcium 
carbonate.  Barytes  is  the  most  common  adulterant,  being  cheap 
and  heavy.  A  pure  white  lead  should  dissolve  in  dilute  C.P.  nitric 
acid,  without  leaving  a  residue.  (Common  nitric  acid  will  not  yield 
a  perfect  solution,  as  it  contains  sulphuric  acid.) 

White  lead  is  very  heavy,  having  a  specific  gravity  of  6.47.  A 
cubic  foot  of  the  dry  powder  weighs  about  185  pounds.  It  has 
great  value  as  a  pigment,  owing  to  its  covering  power,  its  perma- 

*  Mineral  Industry,  VIII,  392  ;  IX,  438.  J.  Soc.  Chem.  Ind.,  1895,  975  ;  1897, 
743. 


PIGMENTS  229 

nency,  and  the  readiness  with  which  it  mixes  with  other  pigments. 
But  it  turns  dark  on  contact  with  hydrogen  sulphide,  or  if  mixed 
with  pigments  containing  sulphur,  such  as  ultramarine,  cadmium 
yellow  (CdS),  or  vermilion  (HgS).  It  is  not  suitable  for  painting 
the  interiors  of  houses  where  gas  or  coal  is  burned.  It  is  nearly 
insoluble  in  water,  but,  if  taken  into  the  system,  will  in  time  produce 
very  dangerous  poisoning;  and  too  much  care  cannot  be  taken  in 
the  manufacture  to  prevent  the  fine  dust  from  flying  about.  Sponges 
are  worn  over  the  mouth  by  the  workmen,  especially  in  the  grinding 
room.  An  exhaust  fan  should  be  employed  to  draw  the  dust  away 
from  the  workmen. 

Owing  to  the  cost  and  poisonous  character  of  white  lead,  substitutes 
are  used  to  some  extent.  These  are  lead  sulphate;  sulphite,  and  oxy- 
chloride.  Lead  sulphate  is  the  base  of  "  sublimed  white  lead,"  the 
chief  white  lead  substitute.  By  heating  galena  and  coke  in  a  blast  of 
hot  air,  part  of  the  lead  is  reduced  to  the  metallic  state,  and  part 
converted  to  sulphate  and  oxide,  which,  together  with  some  metallic 
lead,  sublime  as  "  lead  fume."  This  is  collected  in  chambers  and  sub- 
jected to  a  second  heating  in  a  blast  of  hot  air,  which  finishes  the  con- 
version to  sulphate.  The  zinc  present  in  the  galena  also  passes  off 
with  the  fume,  and  is  converted  to  zinc  white  by  the  hot-air  blast. 
The  color  of  the  sublimed  white  lead  is  sometimes  improved  by  treat- 
ing with  sulphuric  acid.  It  has  good  covering  power  and  color,  and 
is  not  readily  affected  by  hydrogen  sulphide.  It  mixes  well  with  other 
pigments  containing  sulphur,  and  is  non-poisonous. 

Lead  sulphite  is  made  by  precipitating  a  basic  acetate  solution 
with  sulphur  dioxide  gas,  or  by  subliming  mixed  lead  and  zinc  ores 
with  carbon,  with  a  limited  supply  of  hot  air. 

Pattinson's  white  lead  is  an  oxychloride  of  lead  (PbCl  •  OH), 
made  by  precipitating  a  hot  solution  of  lead  chloride  with  one-half 
the  quantity  of  milk  of  lime  necessary  for  its  complete  decomposi- 
tion. The  pigment  has  good  body  and  color,  but  is  not  now  used. 

White  zinc,  or  Chinese  white,  is  zinc  oxide  (ZnO).  It  is  made  by 
distilling  metallic  zinc  in  fire-clay  retorts,  and  leading  the  vapors 
into  a  flue  through  which  air  is  drawn.  On  contact  with  the  air, 
the  hot  vapor  at  once  inflames  and  burns  to  the  oxide,  which  is  col- 
lected in  a  series  of  settling  chambers,  or  in  large  bags  of  cotton 
cloth,  the  gas  and  air  escaping  through  the  meshes  of  the  cloth. 
Instead  of  the  metal,  zinc  ores  mixed  with  carbon  (e.g.  coke  or  coal), 


230  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

are  heated  in  special  furnaces  or  retorts,  the  vapors  being  burned  with 
air  as  before.  But  ores  containing  cadmium  cannot  be  used,  because 
cadmium  oxide  also  sublimes,  and  being  brown,  discolors  the  product. 
The  oxide  is  also  formed  by  calcining  zinc  carbonate  or  hydroxide. 
The  natural  carbonate,  Smithspnite,  is,  however,  seldom  pure  enough, 
and  precipitated  carbonate  must  be  used.  This  is -too  expensive  to 
compete  with  the  combustion  process. 

Zinc  white  is  very  permanent,  and  works  well  in  water  and  in  oil, 
of  which  latter  it  requires  a  large  amount,  usually  about  20  per  cent 
of  its  weight. 

Zinc  sulphide  is  sometimes  substituted  for  zinc  white.  This  has 
more  body  than  the  oxide.  If  the  vapors  of  zinc  and  sulphur  are 
brought  together,  zinp  sulphide  is  formed ;  it  is  collected  in  settling 
chambers  from  which  the  air  is  excluded.  As  a  rule,  pure  sulphide 
is  not  used,  but  a  mixture  of  sulphide  and  barium  or  strontium 
sulphate.  Zinc  sulphide  whites  are  permanent,  have  good  body  and 
color,  and  mix  well  with  oil  and  with  other  pigments,  excepting  those 
containing  lead  or  copper. 

Lithopone  is  a  mixture  of  barium  sulphate  and  zinc  sulphide. 
Hot  solutions  of  barium  sulphide  and  zinc  sulphate  are  mixed;  the 
precipitate,  after  filtering  and  washing,  is  dried,  ground  with  a  little 
ammonium  chloride,  and  the  mass  heated  red  hot  and  quenched  by 
pouring  into  water.  After  grinding  and  levigating,  a  fine  white 
powder  is  obtained,  which  works  well  in  oil,  has  good  body,  is  not 
readily  affected  by  hydrogen  sulphide,  and  is  somewhat  cheaper  than 
white  lead.  It  finds  much  use  in  paints  and  varnish  enamels,  for  oil- 
cloths, and  as  filler  in  rubber  compounding. 

The  barium,  sulphide  required  is  made  by  reducing  barytes  with 
coal  dust,  by  calcining  in  a  rotary  furnace  or  in  a  reverberatory.  The 
charge  is  then  lixiviated,  hot,  and  the  solution  clarified  by  filtration. 

Barytes,  or  barium  sulphate,  occurs  native  in  large  quantities. 
The  mineral  is  finely  ground,  treated  with  hydrochloric  acid  or  with 
sulphuric  acid  to  remove  iron,  and  then  levigated.  Precipitated 
barium  sulphate  (blanc  fixe)  is  obtained  as  a  by-product  in  some 
chemical  industries,  and  is  used  to  a  considerable  extent  as  a  filler 
and  pigment.  It  has  more  body  than  barytes. 

Barytes  is  very  heavy,  is  not  affected  by  sulphur  nor  other  chem- 
icals, and  may  be  mixed  with  all  pigments.  It  has  little  body,  and 
does  not  work  well  in  oil,  having  a  streaky  appearance  when  applied, 
and  drying  very  slowly.  Owing  to  its  weight,  one  of  its  chief  uses 
is  to  adulterate  white  lead. 


PIGMENTS  231 

Gypsum,  terra  alba,  or  mineral  white,  is  used  to  some  extent 
as  a  pigment,  especially  for  wall-paper  printing.  The  mineral  is 
simply  ground,  and  treated  with  acid  to  remove  the  iron.  Precip- 
itated calcium  sulphate  is  a  by-product  of  many  chemical  opera- 
tions, and  is  largely  used  as  a  filler  in  paper  making,  and  for 
weighting  cloth,  under  the  names  "  Crown  filler "  and  "  Pearl 
hardening." 

Whiting,  or  Paris  white,  is  calcium  carbonate.  It  is  prepared  by 
grinding  and  levigating  pure  chalk,  which  occurs  in  large  deposits 
in  England,  France,  and  other  countries.  Precipitated  calcium  car- 
bonate is  a  by-product  from  many  chemical  processes.  Whiting  is 
much  used  to  modify  the  shade  of  other  pigments,  and  as  the  bases 
of  whitewash.  When  mixed  with  from  15  to  18  per  cent  of  linseed 
oil,  it  forms  putty. 

Kaolin,  or  China  clay  (p.  212),  is  sometimes  used  to  modify  the 
shade,  or  to  adulterate  other  pigments.  Its  chief  uses  as  pigment 
are  in  wall-paper  printing,  and  as  filler  in  cloth  and  paper. 

BLUE  PIGMENTS 

Ultramarine  is  the  most  important  blue  pigment.  It  occurs  in 
nature  as  the  mineral  lapis  lazuli,  but  in  such  small  quantities,  and 
the  cost  of  preparation  is  so  great,  that  this  is  of  no  importance  as 
the  source  of  the  pigment. 

Ultramarine  is  probably  a  double  silicate  of  sodium  and  alu- 
minum, together  with  a  sulphide  of  sodium.  But  the  composition 
varies  in  different  samples  having  the  same  physical  properties. 
The  presence  of  sulphides  seems  necessary  for  the  color,  since,  if 
treated  with  acid,  hydrogen  sulphide  is  evolved,  and  the  color  dis- 
appears. Numerous  formulae  have  been  proposed  for  ultramarine. 
Soda  ultramarine,  poor  in  silica,  is  4(Na2Al2Si2Og)  +  Na2S4 ;  *  that 
high  in  silica  is  2(Na2Al2Si3O10)  +  Na2S4.* 

Soon  after  the  introduction  of  the  Leblanc  soda  process,  blue 
spots,  resembling  natural  ultramarine  in  color,  were  noticed  in  soda 
furnaces  lined  with  siliceous  material.  This  suggested  the  possi- 
bility of  artificial  ultramarine.  In  1828,  Guimet  in  France  and 
Gmelin  in  Germany  succeeded  in  making  it.  Guimet  kept  his  method 
secret,  but  Gmelin  published  his.  Afterwards,  green,  violet,  and 
yellow  ultramarine  were  discovered.  A  white  ultramarine  is  sup- 
posed to  be  the  basis  of  all  others,  and  to  it  is  assigned  the  formula : 

*  Annalen  der  Chemie,  194,  1.  —  R.  Hoffmann. 


232  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

Na2Al2Si2O8  +  Na2S.*  Green  ultramarine  is  probably  not  a  distinct 
chemical  compound,  but  a  mixture  of  ultramarines. 

None  of  the  above  ultramarines,  excepting  blue  and  green,  has 
any  commercial  importance. 

The  materials  used  for  making  ultramarines  are  China  clay, 
sodium  carbonate  or  sulphate,  carbon,  sulphur,  and  sometimes  si- 
liceous matter.  The  purity  of  the  material  is  important  as  affecting 
the  shade  of  the  color ;  iron  is  especially  liable  to  make  it  dull.  There 
are  two  methods  of  making  it,  the  sulphate  of  soda,  or  indirect  method, 
and  the  soda-ash,  or  direct  method. 

In  the  sulphate  method,  kaolin,  anhydrous  sodium  sulphate,  and 
charcoal,  or  pure  coal,  are  powdered  and  thoroughly  mixed.  The  car- 
bon is  necessary  to  reduce  the  sulphate  to  sulphide.  Sometimes  rosin 
is  used  as  a  reducing  substance.  The  kaolin  should  contain  2  SiO2  to 
1  A12O3,  and  be  as  finely  powdered  as  possible.  The  mixture  is  packed 
in  crucibles  f  having  tight-fitting  covers,  and  is  heated  at  a  bright  red 
heat  for  about  8  hours.  The  furnace  is  allowed  to  cool  very  slowly, 
care  being  taken  that  no  air  has  access  to  the  contents  of  the  crucibles. 
When  cold,  the  mass  is  dull  green  and  porous,  and  when  ground  and 
washed  constitutes  the  ultramarine  green  of  commerce.  It  is  obtained 
by  this  process  only. 

To  make  the  blue  ultramarine,  the  green  powder  is  subjected  to 
a  "  coloring  "  process.  It  is  spread  in  shallow  trays  in  layers  about 
1  inch  deep,  and  sprinkled  with  powdered  sulphur.  On  heating,  the 
sulphur  ignites,  and  is  allowed  to  burn  itself  out  with  access  of  air. 
Sometimes  muffles  are  used,  the  sulphur  being  added  in  small  quan- 
tities at  a  time,  and  the  charge  stirred  with  mechanical  stirrers  dur- 
ing heating.  A  part  of  the  sodium  sulphide  is  probably  changed  to 
the  sulphate  or  other  soluble  salts,  and  the  crude  blue  results.  It 
is  powdered  and  washed  to  remove  soluble  salts  (Na2SO4,  Na2SO3), 
and  sometimes  boiled  with  a  sodium  sulphide  solution  to  remove 
any  free  sulphur,  which  is  injurious  to  the  copper  print  rolls  in 
calico  printing.  It  is  then  ground  and  levigated,  the  different 
grades  being  used  for  different  purposes.  The  shade  is  usually 
modified  to  match  certain  standards,  by  blending  several  lots  of 
colors. 

The  soda-ash,  or  direct,  method  yields  blue  ultramarine  at  one 

*  Annalen  de  Chemie,  194,  1.  —  R.  Hoffman. 

f  In  modern  plants,  muffle  furnaces  are  replacing  the  crucibles  for  making  the 
green  ultramarine.  But  these  must  be  built  very  carefully  to  exclude  the  air ;  then 
£hey  need  much  time  for  cooling,  usually  requiring  10  days  or  more. 


PIGMENTS  233 

heating,  which  may  be  done  in  muffles  or  in  crucibles.  The  usual 
charge  is  about  2j  tons,  and  consists  of  soda-ash,  kaolin,  charcoal, 
and  sulphur,  ground  fine  and  packed  firmly  on  the  floor  of  the  muf- 
fle, forming  a  layer  about  14  inches  thick.  A  layer  of  tiles,  luted 
together  with  clay,  is  placed  on  top  of  the  charge,  and  the  front  of 
the  furnace  is  bricked  up,  a  loose  brick  being  left  so  that  samples 
may  be  taken  out  to  determine  the  time  of  heating.  The  process  is 
very  slow,  requiring  3  or  4  weeks,  of  which  10  or  12  days  are  required 
for  the  slow  cooling  of  the  muffle;  during  all  this  time  great  care  is 
necessary  to  exclude  the  air.  The  mass  forms  two  layers,  one  bright 
blue,  and  the  bottom  greenish  blue.  These  are  separated,  washed, 
and  levigated.  By  using  large  crucibles  instead  of  the  muffle,  the 
time  of  heating  is  reduced  somewhat,  but  the  breakage  and  extra 
labor  more  than  offset  the  gain. 

To  make  an  ultramarine  which  is  less  sensitive  to  acids,  and  which 
will  withstand  the  alum  used  in  paper  making,  a  high  percentage 
of  silica  in  the  pigment  is  necessary.  For  such  a  product,  it  is  cus- 
tomary to  use  the  soda  process,  and  to  add  powdered  quartz,  sand,  or 
diatomaceous  earth  to  the  charge. 

The  first  heating  is  very  important  in  all  processes  of  making 
ultramarine  blue;  about  700°  C.  is  the  proper  temperature.  If  over- 
heated, the  mass  may  fuse.  Exclusion  of  air  is  necessary  to  prevent 
oxidation  and  loss  of  sulphur,  which  causes  the  product  to  turn  dull 
green,  brown,  or  gray. 

Ultramarine  blue  is  much  used  in  wall-paper  and  calico  printing ; 
for  neutralizing  the  yellow  color  in  paper  pulp,  crystallized  sugar, 
and  cotton  and  linen  goods ;  for  laundry  blue ;  for  paint ;  for  printers' 
ink ;  and  for  coloring  mottled  soaps.  It  is  a  very  fast  color  to  light, 
soap,  and  alkalies,  but  is  quickly  destroyed  by  even  weak  acids. 

Ultramarine  violet  is  made  by  heating  the  blue,  rich  in  silica, 
to  175°  C.,  in  an  atmosphere  of  chlorine  and  steam.  Some  of  the 
sodium  is  thus  converted  to  salt,  and  removed  by  washing.  The 
violet  may  also  be  formed  by  heating  the  blue  to  about  200°  C.,  with 
2  or  3  per  cent  ammonium  chloride,  in  the  presence  of  air.  It  is  not 
much  used,  as  it  has  little  tinctorial  power. 

Ultramarine  red  is  made  by  heating  the  blue  to  not  over  145°  C., 
in  an  atmosphere  .of  dry  hydrochloric  acid  gas,  or  in  the  vapors  of 
nitric  acid.  It  is  of  but  little  importance. 

Prussian  blue,  or  Berlin  blue,  is  the  ferrocyanide  of  iron  (ferric- 
ferrocyanide),  Fe4[Fe(CN)6]3.  To  make  it,  a  dilute  solution  of  cop- 


234  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

peras  (FeSO4  •  7  H^O),  acidified  with  sulphuric  acid,  is  precipitated 
with  potassium  ferrocyanide  solution.  After  decanting  the  liquor 
the  white  precipitate  of  ferrous-ferrocyanide  is  oxidized  with  nitric 
acid,  or  with  bleaching  powder  and  hydrochloric  acid.  Exposure  to 
the  air  also  causes  oxidation,  but  the  color  thus  obtained  is  not  so 
good. 

Chinese  blue  is  a  very  pure  and  carefully  prepared  Prussian  blue. 
In  order  to  lighten  the  shade,  and  to  make  the  pigment  easier  to 
grind,  a  certain  amount  of  alum  is  added  to  the  copperas  solution 
before  precipitating. 

A  blue  which  is  soluble  in  water  results  if  the  iron  solution  is 
poured  into  the  ferrocyanide  solution  in  a  slow  stream,  or  if  Prus- 
sian blue  is  boiled  in  a  ferrocyanide  solution.  In  both  cases,  the 
ferrocyanide  must  be  in  excess. 

Prussian  blue  is  not  affected  by  acids,  and  mixes  well  with  oil, 
but  fades  a  little  on  exposure  to  the  light.  The  color  is  destroyed 
by  alkalies,  and  consequently  it  cannot  be  mixed  with  any  sub- 
stance having  an  alkaline  reaction.  It  has  great  tinctorial  power, 
but  is  transparent,  and  lacks  body.  It  is  dissolved  by  oxalic  acid, 
yielding  a  blue  solution,  formerly  much  used  for  blue  ink. 

TurnbulTs  blue,  a  deep  reddish  blue  precipitate,  is  obtained  by 
precipitating  a  ferrous  salt  with  potassium  ferricyanide  [KsFe(CN)6], 
instead  of  the  ferrocyanide.  This  is  similar  to  Prussian  blue. 

Smalt  is  a  potash-cobalt  glass,  made  by  fusing  pure  sand  and 
potash  with  cobalt  oxide  (Co2O3),  in  a  furnace  similar  to  a  glass  fur- 
nace. The  crude  cobalt  oxide,  called  "  zaffre,"  is  made  by  carefully 
roasting  smaltite  (CoAs2),  cobaltite  (CoAsS),  or  cobalt-nickel  py- 
rites [(CoNi^Ss].  The  ore  is  carefully  sorted  by  hand,  and  iron 
pyrites  and  other  impurities  removed;  then  it  is  ground  and  some- 
times levigated,  and  roasted  in  a  reverberatory  furnace.  A  large 
part  of  the  arsenic  and  sulphur  passes  off  as  oxides.  The  arsenic 
trioxide  (As2O3)  is  condensed  in  long  flues  or  chambers,  while  the 
sulphur  dioxide  escapes  to  the  chimney.  A  small  amount  of  the 
sulphur  and  arsenic  is  left  in  the  zaffre  to  combine,  during  the 
fusion,  with  the  iron,  copper,  nickel,  and  other  injurious  metals,  form- 
ing a  speiss,  which,  being  heavier  than  the  glass,  settles  to  the  bottom 
of  the  pot.  The  blue  glass  is  refined  (p.  203)  until  all  the  impurities 
have  settled,  and  is  then  ladled  out  into  water.  This  granulates 
it,  and  the  sand  so  formed  is  ground  under  edge-runners  and  levi- 
gated. The  medium-fine  deposit  is  the  best  grade,  the  finest  being 


PIGMENTS  235 

too  light-colored.  The  coarse  and  the  very  fine  are  usually  re- 
melted. 

Smalt  is  a  very  permanent  color,  fast  to  light,  and  not  affected  by 
acids  nor  alkalies.  But  it  does  not  work  well  as  a  paint  either  in 
oil  or  in  water,  and  is  expensive;  hence  it  is  now  largely  replaced 
by  ultramarine.  The  composition  of  commercial  smalt  varies  much ; 
it  may  contain  from  2  to  16  per  cent  of  cobaltous  oxide  (CoO),  but 
it  is  often  difficult  to  get  a  good  test  for  the  cobalt. 

Imitation  smalt  is  sometimes  made  of  sand,  colored  with  ultra- 
marine. A  simple  test  with  acid  detects  this  at  once.  Prussian 
blue  is  shown  by  treating  with  alkali. 

Cobalt  blue  is  made  as  follows :  alumina  is  heated  to  a  red  heat 
in  a  crucible  with  basic  cobalt  phosphate,  made  by  adding  sodium 
phosphate  to  a  cobalt  nitrate  solution.  Alum  and  sodium  car- 
bonate solutions  are  mixed,  and  aluminum  hydroxide  precipitated. 
These  two  products  are  thoroughly  washed,  and  one  part  cobalt 
phosphate  is  mixed  with  8  parts  aluminum  hydroxide,  and  the  mix- 
ture heated  to  a  red  heat  until  the  blue  color  develops.  The  pigment 
is  then  ground  wet,  washed,  and  dried.  This  yields  a  good  oil  color. 

Copper  blues  are  not  important.  Mountain  blue  is  the  ground 
mineral  azurite,  a  hydrated  copper  carbonate  [2  CuCO3,  Cu(OH)2]. 

Bremen  blue  is  a  copper  hydroxide  containing  some  copper  car- 
bonate and  oxy chloride.  A  mixture  of  common  salt,  copper  sul- 
phate, and  metallic  copper  in  small  pieces  is  kept  in  tubs  for  several 
weeks,  being  well  stirred  frequently.  A  paste  of  green  oxy  chloride 
is  formed,  which  is  washed  free  from  all  soluble  salts.  A  small 
quantity  of  hydrochloric  acid  is  then  added,  and  left  for  several 
hours.  Finally,  a  solution  of  caustic  soda  is  added,  and  thoroughly 
mixed  until  the  paste  acquires  a  blue  color.  After  washing  well 
and  drying,  it  is  ready  for  use. 

The  copper  blues  are  altered  somewhat  by  exposure  to  the  weather. 
They  are  readily  darkened  by  hydrogen  sulphide  or  sulphur  fumes, 
so  cannot  be  mixed  with  pigments  containing  sulphur.  They  dis- 
solve in  acids  and  in  ammonia,  and  become  black  when  heated, 
owing  to  the  formation  of  cupric  oxide  (CuO).  They  are  opaque 
in  water,  but  become  slightly  transparent  in  oil  and  lose  body.  They 
are  at  best  a  greenish  blue. 

Indigo  is  an  organic  substance  (p.  521)  somewhat  used  as  a  pig- 
ment in  laundry  blue  and  soap. 


236  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


GREEN  PIGMENTS 

Ultramarine  green  is  not  largely  used  as  a  pigment.  Its  prepara- 
tion is  described  on  p.  232. 

True  Brunswick  green  is  the  oxychloride  of  copper,  made  by 
allowing  metallic  copper  to  stand  for  a  number  of  weeks  in  a  solu- 
tion of  common  salt  which  contains  sulphates.  The  insoluble  pig- 
ment is  washed  through  a  sieve  to  remove  copper  chips,  and  then 
dried  at  a  low  temperature  to  prevent  decomposition.  It  is  a  good 
pigment,  working  well  with  oil,  and  having  a  fair  coloring  power; 
but  the  color  is  rather  pale. 

The  pigment  now  sold  under  the  name  of  Brunswick  green  is 
generally  a  mixture  of  Prussian  blue,  chrome  yellow,  and  barytes, 
the  proportion  of  each  depending  on  the  shade  desired.  These 
greens  are  prepared  by  the  dry  or  the  wet  methods.  In  the  former, 
the  dry  ingredients  are  mixed  in  a  paint-  or  edgerunner-mill.  But 
the  shade  is  inferior  to  that  produced  by  the  wet  method.  In  this, 
copperas  (FeSC>4  •  7  H^O),  lead  acetate,  barytes,  and  potassium 
ferrocyanide  and  bichromate  are  used.  The  iron  and  lead  salts  are 
dissolved  separately,  and  mixed  while  stirring  in  the  barytes;  some 
lead  sulphate  is  thus  precipitated  also.  Then,  while  still  stirring 
actively,  the  mixture  of  potassium  ferrocyanide  and  bichromate  solu- 
tion is  added.  After  a  few  moments'  further  stirring,  the  pigment  is 
allowed  to  settle,  and  the  liquor  is  decanted.  Then  the  precipitate 
is  washed  by  decantation,  filtered,  and  dried  carefully.  Or  the  dry 
ingredients  are  finely  powdered,  and  then  stirred  up  thoroughly  with 
water  in  a  tank  until,  on  settling,  the  liquor  is  nearly  colorless.  The 
precipitate  is  washed  as  above  described. 

These  greens  are  sometimes  sold  under  the  names  Victoria,  Prus- 
sian, or  chrome  green.  They  work  very  well  in  oil,  have  good  cov- 
ering power,  and  are  fairly  permanent;  but  they  cannot  be  mixed 
with  pigments  containing  sulphur  or  alkaline  substances,  nor  used 
where  exposed  to  hydrogen  sulphide  gas.  Alkalies  act  both  upon 
the  Prussian  blue  and  the  chrome  yellow,  causing  them  to  turn  red 
or  brown.  Sulphur  darkens  the  chrome  yellow. 

Chrome  greens  are  valuable  pigments,  having  a  light  yellowish 
green  color.  The  basis  is  chromic  oxide  (Cr2O3).  By  precipitat- 
ing a  solution  of  a  chromic  salt  with  soda,  chromium  hydroxide 
[Cr(OH)3]  is  obtained.  This  is  washed,  dried,  and  calcined  at  a 
red  heat,  until  the  water  is  expelled,  and  chromic  oxide  results. 


PIGMENTS  237 

Guignet's  green  *  is  a  chrome  green  made  in  the  dry  way.  A 
mixture  of  3  parts  potassium  bichromate  with  8  parts  boric  acid 
is  heated  to  dull  redness  in  a  reverberatory  furnace  for  four  hours. 
The  porous  mass  is  then  washed,  ground,  and  dried.  In  composi- 
tion, this  green  is  a  hydrated  chromic  oxide,  containing  a  very  small 
quantity  of  boric  acid.  A  chromium  borate  is  formed  by  the  calci- 
nation, which  is  decomposed  by  the  water,  forming  hydrated  chro- 
mic oxide  (Cr2O3  •  2  H2O),  or  Cr2O(OH)4,  and  regenerating  boric 
acid. 

Guignet's  green  is  permanent,  mixes  well  with  oil  and  with  all 
other  colors,  and  has  good  covering  power.  It  is  one  of  the  most 
valuable  pigments. 

Chrome  greens,  consisting  of  chromium  phosphate,  are  sometimes 
made  by  boiling  potassium  bichromate  with  sodium  phosphate  and  a 
reducing  agent.  These  are  not  so  good  as  the  oxides,  and  have  paler 
shades. 

Copper  greens  containing  only  copper  salts  are  of  little  impor- 
tance. Only  two  need  be  considered  here. 

Mountain  green,  malachite,  or  mineral  green,  is  a  basic  copper 
carbonate  [CuCOs,  Cu(OH)2],  occurring  as  the  mineral  malachite, 
which  is  much  used  for  ornamental  bric-a-brac  and  lapidary  work. 
When  ground  very  fine,  it  is  sometimes  used  as  a  pigment,  and  is 
permanent  in  the  light,  misses  well  with  oil,  and  has  fair  covering 
power.  It  is  blackened  by  hydrogen  sulphide.  An  inferior  imita- 
tion of  the  natural  product  is  made  by  precipitating  copper  sulphate 
solution  with  sodium  or  potassium  carbonate  containing  a  little  white 
arsenic  (As2Oa). 

Verdigris  is  not  of  constant  composition,  but  is  a  basic  copper 
acetate,  corresponding  nearly  to  trie-formula  [2  Cu(C2H3O2)2  +  CuO]. 
It  is  sometimes  made  by  covering  copper  plates  in  heaps  of  the  resi- 
due from  wine  presses.  Fermentation  of  the  mass  produces  acetic 
acid,  which,  together  with  the  moisture,  forms  a  layer  of  verdigris 
on  the  copper.  This  is  scraped  off,  washed,  and  levigated.  A  better 
product  is  obtained  by  wetting  cloths  in  vinegar  or  in  pyroligneous 
acid,  and  spreading  them  between  the  copper  plates.  Verdigris  is 
not  a  good  pigment,  being  altered  by  moisture  and  light. 

By  dissolving  copper  oxide,  or  carbonate,  in  acetic  acid,  and 
evaporating  the  solution,  a  crystallized  salt  having  the  composition 

*  Bulletin  de  la  Soci6t6  de  Paris,  1,  9.  Guignet,  —  Fabrication  des  Couleurs, 
149-153. 


238  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

Cu(C2H3O2)2,  Cu(OH)2  •  H2O  is  obtained,  which  is  called  "  distilled 
verdigris  "  in  trade.  This,  however,  is  not  a  pigment. 

Copper  and  arsenic  greens  surpass  all  others  in  brilliancy  and 
beauty,  but,  being  exceedingly  poisonous,  cannot  be  used  for  many  pur- 
poses. Scheele's  green,  which  is  chiefly  copper  arsenite  (HCuAsO3), 
is  made  by  dissolving  arsenious  acid  in  a  hot  solution  of  potassium 
carbonate,  and  pouring  the  liquid  into  a  solution  of  copper  sulphate. 
The  precipitate  is  carefully  washed  and  dried.  It  is  a  grass-green 
pigment,  having  little  coloring  power,  and  now  seldom  used. 

Paris,  or  emerald,  green  is  an  aceto-arsenite  of  copper, 

[Cu(C2H3O2)2  •  CusAsfeOe], 

prepared  by  adding  a  thin  paste  of  verdigris  in  water  to  a  boiling 
solution  of  arsenious  acid  in  water;  some  acetic  acid  is  then  added, 
and  the  mixture  boiled  until  the  precipitate  is  of  the  desired  shade ; 
or  the  color  will  develop  by  simply  allowing  the  mixture  to  stand 
for  some  days.  By  Galloway's  process,  sufficient  sodium  carbonate 
is  added  to  a  copper  sulphate  solution  to  precipitate  one-fourth  of 
the  copper.  Then  acetic  acid  is  added  until  the  precipitate  is  just 
redissolved,  and  the  liquid  is  heated  to  boiling.  A  hot  solution  of 
sodium  arsenite  (arsenious  acid  dissolved  in  sodium  carbonate)  is 
then  added,  and  the  mixture  well  stirred.  The  green  precipitate  is 
filtered,  washed,  and  dried  at  a  low  ^temperature.  For  the  finest 
pigment,  the  solutions  should  be  dilute. 

Paris  green  has  a  peculiar  light  green  shade  possessed  by  no 
other  pigment.  It  is  permanent,  works  well  in  oil,  and  has  a  good 
covering  power.  But  owing  to  its  poisonous  character  its  use  as  a 
pigment  is  much  restricted.  Nearly  the  whole  of  the  present  pro- 
duction is  used  to  exterminate  potato  beetles  and  other  insects  inju- 
rious to  vegetation. 

Terra  verde  is  an  earthy  pigment,  containing  ferrous  silicate  as 
its  chief  ingredient.  Green  earths  are  found  in  numerous  places, 
but  the  best  are  from  Cyprus  and  Italy.  They  are  a  dull  pale  green, 
and  are  permanent,  but  have  little  covering  power. 

YELLOW  PIGMENTS 

The  most  important  yellow  pigments  are  chrome  yellows  and 
yellow  ochres ;  others  are  used  but  little. 

Chrome  yellows  have  as  a  basis  the  chromate  of  lead,  zinc,  or 
barium,  are  all  made  by  precipitation  and  each  has  a  shade  peculiar 


PIGMENTS  239 

to  itself.  Lead  chromate  is  made  from  the  lead  acetate,  or  nitrate, 
and  potassium  bichromate.  The  reactions  are  as  follows :  — 

a)  2  Pb(C2H302)2+K2Cr207+H20  =  2  KC2H3O2+2  C2H4O2+2  PbCrO4. 
6)  2  Pb(NO3)2  +  K2Cr2O7  +  H2O  =  2  KNO3  +  2  HNO3  +  2  PbCrO4. 

In  order  to  modify  the  shade,  lead,  barium,  or  calcium  sulphate  is 
mixed  with  the  chromate  in  the  grinding-mill.  Or  a  portion  of  the 
lead  is  precipitated  as  sulphate  or  carbonate  along  with  the  chro- 
mate ;  this  is  done  by  mixing  sodium  carbonate  or  sulphate  with  the 
potassium  bichromate.  Chrome  yellows  are  called  "  pure  "  when 
lead  sulphate  has  been  used  to  modify  the  shade. 

The  precipitate  is  well  washed  by  decantation,  and  the  pulp 
freed  from  water  in  the  filter  press,  or  in  a  centrifugal  machine,  or 
by  pressing  in  cloth  bags.  It  should  be  dried  at  a  low  temperature, 
and  well  ground  either  dry  or  in  oil.  For  the  best  color,  the  lead 
nitrate  should  be  used  in  slight  excess.  When  lead  nitrate  is  used 
in  making  the  chromate,  it  is  customary  to  recover  the  potassium 
nitrate  from  the  liquor  and  first  wash-waters,  the  free  nitric  acid 
being  neutralized  with  pearlash  before  evaporating.  The  excess  of 
lead  salt  is  precipitated  from  the  waste  liquors  on  the  addition  of 
the  pearlash. 

Chrome  yellow  is  sometimes  made  by  digesting  lead  sulphate 
with  a  hot  solution  of  potassium  bichromate  until  the  desired  shade 
is  developed. 

Lead  chromate  is  a  brilliant  yellow,  mixes  well  with  oil,  and  has 
great  covering  power.  It  is  blackened  by  hydrogen  sulphide,  and 
should  not  be  mixed  with  pigments  which  contain  sulphur,  or  are 
strongly  alkaline.  When  treated  with  a  caustic  alkali,  lead  chro- 
mate is  converted  into  a  basic  salt,  having  a  red  or  orange  color. 
These  basic  chromates  are  prepared  for  pigments,  and  sold  under 
the  name  of  chrome  orange  and  chrome  red.  They  are  made  by  boil- 
ing chrome  yellow  with  calcium  or  sodium  hydroxide.  The  follow- 
ing is  the  reaction  involved  :  — 

2  PbCrO4  +  2  NaOH  =Na2CrO4  +  PbCrO4  •  PbO  -  H2O. 

Quicklime  gives  a  paler  color  than  caustic  soda.  Chrome  red  is 
also  made  by  digesting  white  lead  with  potassium  bichromate  and 
caustic  soda. 

Zinc  chromate  is  made  from  zinc  sulphate  and  neutral  potassium 
chromate.  The  neutral  salt  ZnCrO4  forms  only  in  concentrated 
solutions  of  the  precipitant,  and  hydrolyzes  instantly  on  contact 


240  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

with  water  to  basic  chromates,  which  precipitate,  and  to  free  chromic 
acid  in  solution.  The  composition  of  the  precipitate  varies  and  is 
determined  by  the  concentration  of  the  acid  solution  with  which  it  is 
in  contact.  Indefinite  washing  with  water  will  remove  all  of  the 
chromic  acid,  but  after  the  basicity  has  reached  approximately 
4  ZnO  •  CrOs,  the  loss  of  acid  is  slow,  owing  to  the  insolubility  of  the 
precipitate.  Zinc  chromate  is  also  made  by  boiling  zinc  oxide  with 
potassium  bichromate.  The  pigment  has  a  light  lemon  color,  is 
permanent,  not  affected  by  sulphur,  and  can  be  mixed  with  other 
pigments.  It  is  soluble  in  mineral  acids,  and  is  decomposed  by  caustic 
alkalies. 

Barium  chromate  is  much  like  the  zinc  salt,  but  is  a  greenish 
yellow  color.  It  is  made  in  the  same  way  as  is  the  zinc  chromate, 
but  from  barium  chloride.  It  is  not  used  to  any  extent. 

Yellow  ochres  and  Siennas  are  natural  mineral  products,  varying 
from  bright  yellow  to  brown.  The  color  is  due  to  hydrated  oxide  of 
iron,  and  in  Sienna  there  is  a  little  manganese  oxide.  The  pigments 
contain  sand  and  clay  in  large  quantities,  and  are  decomposition 
products  from  iron-bearing  minerals.  The  Siennas  are  usually  finer 
grained  and  contain  less  gangue  mineral  than  the  ochres.  They 
occur  in  beds  in  the  earth,  and  the  only  preparation  necessary  is 
grinding  and  levigating.  They  are  very  permanent,  mix  well  with 
oil  and  with  other  pigments,  have  good  covering  power,  and  are 
cheap.  If  ochres  and  Siennas  are  calcined,  the  water  of  hydration 
is  removed  from  the  ferric  hydroxide,  and  the  color  becomes  orange 
or  red.  Burnt  Sienna,  made  by  heating  raw  Sienna  to  a  low  red 
heat,  is  reddish  orange  in  color. 

Cadmium  yellow  is  cadmium  sulphide  (CdS),  and  is  made  by 
precipitating  a  cadmium  solution  with  hydrogen  sulphide.  If  the 
solution  is  strongly  acid,  the  color  becomes  more  nearly  orange. 

It  is  a  brilliant  yellow,  very  permanent,  and  mixing  well  with 
oil  and  with  other  pigments,  excepting  lead  and  copper  compounds. 
It  is  chiefly  used  as  an  artist's  color.  Sometimes  cadmium  yellow  is 
made  by  using  ammonium  sulphides  instead  of  hydrogen  sulphide 
to  precipitate  the  pigment ;  but  in  this  case  free  sulphur  is  present 
in  the  precipitate,  and  causes  changes  in  the  color  when  mixed  for 
use. 

Orpiment  is  arsenic  trisulphide  (As2S3).  It  is  found  native  as  a 
mineral,  which  is  simply  ground  for  pigment.  It  is  also  extensively 


PIGMENTS  241 

made  by  precipitating  a  dilute  solution  of  arsenious  acid  in  hydro- 
chloric acid  with  hydrogen  sulphide;  or  by  subliming  a  mixture  of 
arsenious  acid  and  sulphur  from  a  retort.  The  pigment  obtained  by 
either  method  is  finely  ground. 

Orpiment  is  a  very  bright  yellow,  mixes  well  with  oil,  and  has 
good  covering  power ;  but  it  is  not  permanent  on  exposure  to  light, 
and  cannot  be  mixed  with  many  other  colors.  It  is  also  very  poison- 
ous. It  is  sold  under  the  name  of  royal  yellow,  or  king's  yellow. 

Litharge  is  lead  monoxide  (PbO),  made  by  oxidizing  metallic 
lead  at  a  high  temperature,  in  rotating  cast-iron  drums,  heated  by 
an  external  fire.  The  drums  have  shelves  or  ribs  inside,  which  pick 
up  the  melted  lead  and  cause  it  to  fall  in  thin  films  through  the  cur- 
rent of  air  drawn  in  by  a  fan.  It  is  not  so  important  as  a  pigment  as 
for  the  preparation  of  "  boiled  linseed  oil  "  (p.  357).  It  is  also  exten- 
sively used  in  making  lead  glass  and  in  pottery  glazes. 

Another  variety  of  lead  monoxide,  having  a  lighter  yellow  shade, 
is  "  massicot,"  which  is  formed  by  oxidizing  lead  at  so  low  a  temper- 
ature that  no  fusion  of  the  product  takes  place.  It  is  chiefly  pre- 
pared for  the  manufacture  of  red  lead  (p.  242). 

Yellow  lead  oxide  is  also  made  by  heating  white  lead. 

Gamboge  is  a  gum-resin  obtained  from  a  tree  (Garcinia  Morella 
Desr.)  of  Siam.  Incisions  are  made  in  the  bark  of  the  tree,  and  the 
sap  is  collected  in  bamboo  receivers,  in  which  the  yellow  resin  is 
left  on  evaporation.  Gamboge  emulsifies  with  water,  and  is  used  as 
a  water-color  paint.  It  cannot  be  used  as  an  oil  paint  except  when 
mixed  with  alumina. 

Indian  yellow,  or  purree,  is  made  by  heating  the  urine  of  cattle 
that  have  been  fed  with  leaves  of  the  mango  tree,  the  color  being 
produced  by  an  excessive  secretion  of  bile,  which  has  passed  into 
the  urine.  The  pigment  precipitates,  and  is  pressed  and  dried;  it 
consists  of  salts  of  euxanthic  acid,  an  organic  body.  It  is  a  bright 
yellow,  but  not  permanent  in  the  light,  and  is  very  expensive. 

ORANGE  PIGMENTS 

Orange  mineral  is  lead  tetroxide  (Pb3O4),  prepared  by  heating 
white  lead  in  the  presence  of  air.  It  is  usually  made  from  the  scum 
which  collects  on  the  surface  of  wash-waters  used  in  levigating  white 

2  PbCO3,  Pb(OH)2  +  O  =  Pb304  +  2  CO2  +  H2O. 

R 


242  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

In  composition  and  properties  it  is  similar  to  red  lead  (below), 
but  has  a  slightly  lower  specific  gravity  (6.95). 

Chrome  orange  has  been  described  in  connection  with  chrome 
yellow  (p.  239). 

Antimony  orange  is  antimony  trisulphide,  made  by  precipitating 
a  moderately  concentrated  solution  of  antimony  chloride  with  hydro- 
gen sulphide.  The  precipitate  is  washed  in  dilute  hydrochloric 
acid,  and  then  levigated.  It  must  be  dried  at  a  low  temperature. 

It  has  a  bright  orange  color  in  oil  or  water,  is  permanent  and  of 
good  body,  but  is  decomposed  by  alkalies.  It  is  chiefly  used  for 
vulcanizing  rubber,  producing  the  red  "  antimony  rubber  "  of  com- 
merce. 

RED  PIGMENTS 

Red  pigments  form  a  numerous  and  important  group,  containing 
some  of  the  brightest  and  most  permanent  colors. 

Red  lead  is  lead  tetroxide  (Pb3O4),  having  the  same  chemical 
composition  as  orange  mineral  (p.  241),  but  differing  in  its  physical 
properties.  It  is  made  by  the  direct  oxidation  of  metallic  lead. 
The  process  is  carried  on  in  two  stages.  In  the  first  or  "  dressing  " 
operation  the  lead  is  converted  into  massicot  by  heating  with  free 
access  of  air  in  a  reverberatory  furnace  to  a  temperature  just  above 
that  of  melted  lead  (340°  C.).  The  temperature  must  be  very  care- 
fully regulated,  for  if  the  massicot  melts  it  passes  into  ordinary 
litharge,  from  which  red  lead  cannot  be  made.  As  fast  as  a  layer  of 
oxide  forms  it  is  pushed  to  the  back  of  the  hearth  with  a  "  rabble  " ; 
finally,  the  unoxidized  lead  is  allowed  to  run  off,  and  the  massicot  is 
raked  out  and  cooled.  It  is  pale  yellow,  of  granular  texture,  and 
contains  pellets  of  unoxidized  lead.  It  is  finally  ground  and  levi- 
gated, and  then  transferred  to  the  second  or  "  coloring  process  " ;  it 
is  heated  to  a  dull  red  heat  in  a  muffle  or  reverberatory  furnace  with 
access  of  air.  The  mass  is  stirred  frequently  to  assist  the  absorption 
of  oxygen,  and  to  develop  the  color.  Samples  are  taken  at  inter- 
vals, until  the  desired  shade  is  obtained,  which  usually  takes  from 
40  to  48  hours ;  then  the  furnace  is  allowed  to  cool.  The  product  is 
usually  ground  before  packing  for  market. 

Red  lead  is  somewhat  variable  in  color,  but  is  a  good  pigment  of 
great  covering  power  and  brilliancy.  It  has  a  specific  gravity  of 
8.5.  Chemically,  it  is  regarded  as  a  mixture  of  lead  monoxide  and 
peroxide  (2  PbO  +  PbC^),  but  commercial  samples  vary  some  from 
this  formula.  When  treated  with  dilute  nitric  acid,  the  monoxide 


PIGMENTS  243 

dissolves,  leaving  the  peroxide  as  a  brown  powder;  this  constitutes 
a  test  for  red  lead,  since  no  other  red  pigment  turns  brown  with  nitric 
acid. 

A  large  use  of  red  lead  is  for  glass  making,  for  which  a  very  pure 
grade  is  necessary.  Owing  to  its  oxidizing  effect  with  linseed  oil,  it  is 
extensively  used,  mixed  with  this  oil,  as  a  lute  in  plumbing  and  gas 
fitting.  It  is  much  used  as  a  protective  paint  for  iron  and  steel. 

Chrome  red  is  a  basic  lead  chromate  (PbCrO4,  PbO  •  H2O),  made 
by  boiling  chrome  yellow  with  caustic  soda  or  with  lime,  as  described 
on  p.  239.  It  is  also  made  by  boiling  white  lead  with  a  solution  of 
neutral  potassium  chromate.  When  the  desired  shade  is  developed, 
the  pigment  is  washed,  ground,  and  levigated. 

It  is  a  fairly  bright  red,  of  good  body,  working  well  in  oil.  Like 
all  lead  pigments,  it  is  darkened  by  sulphur  and  hydrogen  sulphide. 
It  is  sold  as  Chinese  red,  American  vermilion,  and  Victoria  red. 

An  imitation  of  chrome  red  is  made  by  coloring  white  lead,  orange 
lead,  or  barytes  with  some  of  the  coal-tar  dyes,  especially  with  eosins. 

Red  ochre  is  made  by  calcining  ordinary  ochre  at  a  low  red  heat 
until  more  or  less  of  the  water  of  hydration  is  driven  off.  The  shade 
depends  on  the  time  of  heating,  —  the  longer  the  calcination  the  more 
purple  the  product.  Red  ochres  are  essentially  ferric  oxide  with 
alumina,  silica,  and  lime.  The  native  oxides,  hematite  and  limonite, 
are  seldom  used  for  pigment,  being  hard  to  grind.  But  in  a  few  places 
soft  deposits  of  hematite  are  found,  which  yield  a  pale  red  pigment 
without  further  treatment  than  grinding.  These  ochres  are  sold  as 
Indian  red,  light  red,  Venetian  red,  etc. 

Iron  reds  are  now  being  prepared  in  large  quantities,  chiefly  as 
by-products  from  other  manufactures.  These  are  sold  as  rouge, 
colcothar,  Venetian  red,  etc.,  and  all  contain  ferric  oxide  as  the  col- 
oring matter. 

When  fuming  sulphuric  acid  is  made  by  the  dry  distillation  of 
copperas  (p.  82),  a  residue  of  ferric  oxide  remains  in  the  retort.  This 
is  ground,  levigated,  and  sold  as  colcothar.  It  is  nearly  pure  F^Oa. 

In  the  manufacture  of  galvanized  iron  or  tinned  ware,  the  rolled 
sheet  iron  is  dipped  into  a  bath  of  acid  to  dissolve  any  oxide  from 
its  surface  before  putting  it  into  the  bath  of  melted  zinc  or  tin.  These 
acid  "  dipping  liquors  "  contain  much  iron,  which  is  precipitated  by 
adding  soda-ash  or  lime,  and  used  as  pigment.  If  sulphuric  acid  is 
used  in  the  dipping  liquors,  and  is  neutralized  with  lime,  the  precipitate 


244  OUTLINES   OF    INDUSTRIAL   CHEMISTRY 

consists  of  ferric  hydroxide,  with  more  or  less  calcium  sulphate.  By 
calcining,  a  light  red  pigment,  called  Venetian  red,  is  formed. 

Many  metallurgical  operations  yield  liquors  containing  much 
iron,  which  is  precipitated  with  lime,  forming  Venetian  red. 

These  iron  reds  are  very  permanent  and  valuable  pigments. 
They  work  well  in  oil,  mix  with  all  other  pigments,  have  very  good 
body,  and  are  cheap,  but  the  color  is  not  so  bright  as  in  some  pigments. 
The  covering  power  is,  however,  largely  dependent  upon  the  methods 
of  precipitation  and  ignition,  which  are  carefully  guarded  trade  se- 
crets. The  density  of  samples  of  practically  identical  composition 
may  vary  three-  or  four-fold. 

Vermilion  is  mercuric  sulphide  (HgS).  It  occurs  in  nature  as 
the  mineral  cinnabar,  but  the  pigment  is  now  all  made  artificially. 
It  is  one  of  the  brightest  reds,  and  has  been  known  for  a  long  time. 
It  is  made  in  two  ways,  by  the  wet  and  by  the  dry  process.  In 
the  wet  process,  100  parts  of  mercury  are  ground  with  38  parts  of 
flowers  of  sulphur  until  thoroughly  incorporated;  then  the  mass  is 
digested  at  about  45°  C.,  with  a  solution  of  25  parts  caustic  potash  in 
150  parts  water.  The  mixture  is  stirred  frequently,  and  any  water 
lost  by  evaporation  is  replaced.  After  2  or  3  hours  the  mass  becomes 
brown,  and  then  gradually  turns  red.  When  the  desired  color  is 
acquired,  which  usually  takes  about  8  hours,  the  pigment  is  at  once 
washed  by  decantation,  since  further  action  of  the  potash  dulls  the 
color.  The  pigment  is  ground  and  dried  carefully.  The  tempera- 
ture must  be  kept  between  40  and  45°  C.,  for  if  overheated  it  becomes 
brbwn.  Solution  of  potassium  or  sodium  polysulphide  may  be  used 
instead  of  the  potash.  The  brilliancy  of  the  color  may  be  increased 
by  treating  with  hydrochloric  or  nitric  acid. 

The  dry  methods  yield  the  best  product.  The  Dutch  process  con- 
sists in  heating  mercury  and  sulphur  together  in  shallow  iron  pans 
until  they  combine  to  form  a  black  mercuric  sulphide  (HgS,  ethiops 
mineral).  This  is  pulverized,  and  introduced  into  earthenware  re- 
torts in  small  amounts  at  a  time.  The  larger  part  of  the  black  sul- 
phide sublimes  into  the  upper  part  of  the  retort  as  a  bright  red  powder. 
This  is  ground,  washed,  treated  with  acid,  and  levigated. 

Chinese  vermilion  is  the  finest  quality,  and  its  manufacture  was 
long  kept  a  secret.  Now  it  is  known  to  be  made  by  a  process  simi- 
lar to  the  Dutch  method,  but  owing  to  the  patience  and  care  exercised 
by  the  Chinamen  a  very  fine  product  is  obtained. 

Vermilion  is  a  very  heavy,  opaque,  and  brilliant  pigment.     Owing 


PIGMENTS  245 

to  its  weight,  it  settles  out  of  the  oil  when  used  for  paint,  causing 
difficulty  in  applying  it  evenly.  It  is  permanent,  and  not  readily 
affected  by  acids  and  alkalies.  When  heated  in  a  closed  tube,  it 
turns  black,  and  finally  sublimes  unchanged,  thus  furnishing  a  good 
test  for  its  purity.  It  is  sometimes  adulterated  with  red  lead,  iron 
reds,  or  carmine  lakes,  but  these  leave  a  brown  or  black  residue  when 
heated.  Vermilion  is  very  expensive. 

Vermilionettes  are  brilliant  red  pigments,  produced  by  coloring 
neutral  white  bodies,  such  as  barium  sulphate,  lead  sulphate,  or 
white  lead  with  coal-tar  dyes  of  the  eosin  class.  The  white  base  is 
stirred  up  with  a  solution  of  the  dye,  and  lead  acetate  or  alum  is 
added,  which  precipitates  the  color  upon  the  white  base.  Orange 
mineral  is  sometimes  mixed  with  vermilionettes  to  brighten  the 
color.  These  work  well  in  oil,  have  good  body,  and  are  brilliant, 
but  fade  on  exposure  to  the  light. 

Realgar,  the  disulphide  of  arsenic  (As2S2),  occurs  in  nature  in 
small  quantities  as  a  brilliant  red  mineral  which,  when  ground,  fur- 
nishes a  fine  pigment.  But  the  chief  supply  is  obtained  artificially 
by  fusing  together  white  arsenic  (As2O3)  and  sulphur  in  the  proper 
proportions,  or  by  distilling  arsenical  ores  with  sulphur.  The  crude 
product  is  remelted,  and  arsenic  or  sulphur  added,  as  need  be,  to 
give  the  desired  shade.  As  a  pigment,  realgar  is  subject  to  the  same 
disad vantages  as  orpiment  (p.  241).  It  is  much  used,  however,  in 
preparing  "  Bengal  lights,"  and  for  unhairing  hides  for  tanning. 

Antimony  red,  or  antimony  vermilion,  is  an  oxysulphide  of  anti- 
mony, made  by  precipitating  an  antimony  chloride  solution  with 
thiosulphate  of  soda.  On  heating  the  solution  to  55°  C.,  a  red  pre- 
cipitate separates.  This  is  washed  and  dried  at  about  50°  C.  It  is 
also  prepared  by  dissolving  tartar  emetic  in  tartaric  acid  solution, 
mixing  with  sodium  thiosulphate,  and  heating  to  90°  C. 

Antimony  red  is  used  for  oil  and  water  colors,  and  to  some  ex- 
tent in  calico  printing.  It  has  good  body,  and  is  permanent  if  not 
mixed  with  alkalies  or  with  alkaline  vehicles. 

Carmine  pigment  belongs  to  the  class  of  pigments,  called  "  lakes," 
which  are  metallic  salts  of  organic  color  acids.  The  coloring  matter 
in  carmine  is  the  organic  substance  carminic  acid  (CnHisOio),  ob- 
tained from  the  bodies  of  the  cochineal  insect.  The  lake  is  prepared 
by  extracting  the  crushed  insects  with  hot  water,  filtering,  and  adding 
a  solution  of  alum  or  tin  chloride,  and  cream  of  tartar.  After  stand- 


246  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

ing,  the  pigment  precipitates.  Or  the  lake  may  be  precipitated  at 
once  by  adding  sodium  carbonate  to  the  mixed  solutions.  The  extrac- 
tion is  done  in  tinned  copper  vessels,  and  hard  water  is  said  to  improve 
the  color  of  the  pigment. 

Carmine  is  a  very  bright  scarlet,  the  tin  salt  being  brighter  than 
the  aluminum.  It  works  well  in  oil  and  as  a  water  color,  but  fades 
on  exposure  to  sunlight.  It  is  soluble  in  strong  caustic  alkalies. 

Cochineal  lake,  crimson  lake,  Florentine  lake,  and  others,  are  car- 
mine lakes  containing  a  larger  proportion  of  alumina  or  metallic 
base  than  does  carmine. 

Madder  lakes  and  Brazil-wood  lakes  are  prepared  by  precipitat- 
ing extracts  of  these  substances  with  alum  and  tin,  by  adding  so- 
dium carbonate.  They  furnish  red  pigments  of  various  shades,  but 
lacking  in  covering  power. 

Yellow  lakes  are  made  from  fustic,  Persian  berries,  or  quercitron 
bark  extracts,  in  the  same  way  as  the  madder  lakes  are  made. 

Many  of  the  coal-tar  dyes  may  be  precipitated  as  lakes,  and  a 
great  number  of  pigments  are  thus  prepared.  But  many  of  them 
are  deficient  in  covering  power,  and  lack  permanency  on  exposure 
to  the  light. 

BROWN  PIGMENTS 

Umbers  are  ochres  containing  more  manganese  than  Sienna  con- 
tains. They  are  complex  mixtures  of  silica,  alumina,  iron,  manganese, 
lime,  and  other  matter.  There  are  two  varieties,  raw  and  burnt. 
Raw  umber  has  received  no  further  treatment  than  grinding  and 
levigating.  Burnt  umber  has  been  calcined  at  a  low,  red  heat, 
whereby  more  or  less  of  the  water  of  hydration  of  the  iron  oxide  has 
been  driven  out,  giving  a  darker  shade  to  the  product.  The  best 
umber  comes  from  Cyprus,  but  many  other  localities  furnish  it  in 
various  shades.  It  is  very  permanent,  has  good  covering  power,  and 
mixes  well  with  all  other  pigments.  It  is  not  affected  by  acids  nor 
alkalies,  and  is  cheap. 

Vandyke  browns  are  indefinite  mixtures  of  iron  oxides  and  or- 
ganic matter.  They  are  obtained  from  certain  bog-earth  or  peat 
deposits,  or  from  ochres  containing  bituminous  matter.  They  are 
also  made  artificially  from  charred  organic  substances,  such  as  bark, 
cork  cuttings,  or  bone  dust.  Mixtures  of  lampblack,  yellow  ochre, 
and  iron  oxide  are  also  sold  as  Vandyke  browns.  These  pigments 
are  permanent,  mix  well  with  all  other  colors,  and  have  good  body. 


PIGMENTS  247 

Sepia  is  an  organic  pigment  obtained  from  the  cuttle-fish  (Sepia 
officinalis) ,  that  secretes  it  as  a  dark  liquid,  to  be  discharged  in  the 
water  to  hide  his  movements  when  disturbed.  It  is  contained  in  a 
small  sac,  which  is  removed  and  dried.  To  purify  the  pigment,  it 
is  dissolved  in  caustic  soda,  and  the  decanted  solution  is  acidified  with 
hydrochloric  acid.  The  pigment  thus  precipitated  is  washed  and  dried. 

Sepia  is  a  dark  brown,  fine-grained  pigment,  very  permanent  and 
capable  of  mixing  with  all  other  colors.  It  is  chiefly  used  as  a  water 
color  by  artists. 

BLACK  PIGMENTS 

Black  pigments  nearly  all  contain  carbon  as  the  base.  The  most 
important  is  lampblack,  which  is  the  soot  produced  by  the  incom- 
plete combustion  of  organic  substances,  mostly  of  an  oily  or  resinous 
nature.  The  knots  and  refuse  from  pitch  pine  and  hemlock,  the  crude 
mineral  oils,  residues  from  petroleum  refining,  and  the  "  dead  oils  " 
from  coal-tar  furnish  much  lampblack.  The  temperature  of  burning 
is  low  and  the  air  supply  limited,  so  that  a  large  part  of  the  carbon 
remains  unconsumed  and  is  deposited  as  soot  in  a  series  of  chambers, 
through  which  the  combustion  products  are  led.  Some  oil  may 
distil  into  the  chambers,  mixing  with  the  product,  increasing  its 
liability  to  spontaneous  combustion  in  storage,  and  lowering  its  value 
for  paint,  as  it  dries  very  slowly. 

Carbon  black  is  made  by  burning  natural  gas  *  so  that  the  flame 
impinges  upon  a  rotating,  horizontal  iron  plate.  The  sudden  lower- 
ing of  the  temperature  of  the  flame  causes  a  deposit  of  carbon,  which 
is  removed  from  the  plate  as  it  rotates,  by  a  fixed  scraper.  An  au- 
tomatic conveyer  carries  the  pigment  to  the  grinding  and  sifting 
apparatus.  The  product  is  free  from  oily  matter  and  mixes  readily 
in  water,  but  with  difficulty  in  oil.  It  is  much  used  for  printing-ink, 
paint,  rubber  mixing,  coloring  cement  mortar,  etc. 

Carbon  from  different  sources  varies  widely  in  both  covering 
power  and  color.  When  obtained  from  hydrocarbons,  the  higher 
the  molecular  complexity  of  the  substance  burned,  the  less  the  density 
of  the  product,  and  the  browner  the  shade,  although  many  brown 
products  grind  black  in  oil.  Ivory  black  is  the  densest  and  blackest 
pigment,  though  high-grade  bone-black  develops  great  brilliancy  in  a 
paint. 

Ivory-black  is  made  by  heating  the  refuse  from  ivory  working 
in  closed  retorts  until  all  organic  constituents  are  decomposed.  The 

*  Mining  and  Engineering  World,  1911,  Oct.  28.     J.  Soc.  Chem.  Ind.,  1894,  128. 


248  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

retorts  must  not  be  opened  until  quite  cold.  The  charred  mass  is 
ground  fine,  and  yields  the  finest  quality  of  black  pigment  with  respect 
to  deadness  of  the  black  when  ground  in  oil.  It  is  an  intense  black, 
but  since  it  acts  like  bone-char  on  organic  coloring  matter,  it  cannot 
be  mixed  with  most  pigments  of  an  organic  nature. 

Bone-black  is  an  inferior  black,  made  from  bones  charred  in  a  re- 
tort. When  coarsely  pulverized,  it  is  extensively  used  for  decol- 
orizing syrups  and  oils.  It  is  finely  powdered  for  pigment,  and  is 
much  used  in  making  leather  blacking,  where  the  calcium  phosphate 
and  carbonate  in  it  are  also  of  importance 

Charcoal  from  soft  wood,  ground  very  fine,  is  sometimes  used  as 
a  pigment,  and  to  mix  with  other  blacks.  It  is  not  so  soft  and  fine 
as  lampblack. 

Graphite  is  employed  as  a  pigment  in  pencils,  crayons,  and  in 
stove-blacking.  It  also  forms  the  basis  of  a  protective  paint  for 
metal.  It  is  a  dull  black,  very  inert  and  permanent. 

Manganese  ores,  such  as  pyrolusite  (MnCy  and  hausmannite 
(Mn3O4),  are  sometimes  powdered  for  pigments.  But  they  act  as 
"  dryers  "  when  used  with  oil,  and  are  rarely  used  in  paint. 

Black  lake,  made  from  logwood  decoction  and  potassium  bichro- 
mate with  copper  sulphate,  is  a  blue  black,  but  not  permanent. 

Tannate  of  iron  blacks,  derived  from  tannin  liquors,  copperas,  and 
alum,  also  fade  on  exposure  to  the  light. 

REFERENCES 

Lehrbuch  der  Farbenfabrikation.     I.  G.  Gentele,  Braunschweig,   1880. 

Das  Ultramarine.     C.  Fiirstenau,  Wien,  1880.     (Hartleben.) 

Die   Erd-  Mineral-   und   Lackfarben.     Dr.   Mierzinski,   Weimar,    1881. 

Chemistry  of  Pigments.    J.M.Thomson.   Lecture  before  the  Society  for  the 
Encouragement  of  Arts,  Manufactures,  and  Commerce.   London,  1885. 

Fabrication  des  Couleurs.     Ch.  Er.  Guignet,  Paris,  1888. 

Oel  und  Buchdruckfarben.     Louis  E.  Andes,  Leipzig,  1889.     (Hartleben.) 

Die  Fabrikation  des  Ruses  und  der  Schwaerze.     H.   Koehler,   Braun- 
schweig, 1889. 

The  Chemistry  of  Paints  and  Painting.     A.  H.  Church,  London,  1890. 

Painters'   Colours,   Oils,   and  Varnishes.     G.   H.  Hurst,   London,   1892. 

Pigments,  Paints,  and  Painting.     George  Terry,  London,  1893.     (Spon.) 

Die  Fabrikation  der  Mineral-  und  Lackfarben.     J.  Bersch,  Leipzig,  1893. 

Die    Fabrikation    der    Erdfarben.     Dr.    Josef    Bersch,    Leipzig,    1893. 

Handbuch  der  Farben-Fabrikation.     Dr.  S.  Mierzinski,  Leipzig,  1898. 

Chemistry  and  Technology  of  Mixed  Paints.     M.  Tpch,  New  York. 

Modern  Pigments  and  their  Vehicles.     Frederick  Maire,  New  York,  1908. 

An  Introduction  to  the  Chemistry  of  Paints.     J.  N.  Friend,  London,  1910. 

Paint  Technology  and  Tests.     H.  A.  Gardner,  New  York,  1912. 

Journal  of  American  Chemical  Society,  1880,  381.  — H.  Endemann. 

Journal  of  the  Society  of  Chemical  Industry  :  — 

1887,719.   Rawlins.    1890,1137.   Wunder.    1891,709.  1892, 357.  Weber. 

Jour.  Ind.  Eng.  Chem.,  1914,  54. 


BROMINE 

/ 

Bromine  is  widely  distributed  in  nature  as  bromides,  usually 
accompanying  common  salt  and  magnesium  chloride.  The  world's 
supply  is  obtained  from  "  bittern,"  the  mother-liquor  of  the  salt 
industry.  Stassfurt  furnishes  about  two-thirds  of  the  supply,  and 
the  remainder  is  extracted  from  the  brines  found  in  Michigan,  Ohio, 
and  West  Virginia,  along  the  Kanawha  and  Ohio  rivers.  The 
American  product  in  1913  was  about  572,400  pounds.  Small  quan- 
tities are  obtained  from  the  mother-liquors  of  the  Chili  saltpetre 
industry,  and  in  Europe  from  kelp. 

Bromine  is  present  in  the  mother-liquors  as  magnesium  bromide, 
and  to  a  small  extent  as  sodium  bromide;  the  liquors  also  contain 
large  quantities  of  sodium  and  magnesium  chlorides.  Several  methods 
of  extraction  are  in  use,  —  the  continuous  and  periodic  processes 
being  old,  while  recently  direct  electrolysis  of  the  waste  brine  has 
been  introduced.  The  bromine  is  liberated  by  the  current  before  the 
chlorine  is  set  free. 

The  continuous  process  depends  on  the  decomposition  of  the 
magnesium  bromide  by  chlorine  gas.  A  sandstone  or  earthenware 
tower  is  filled  with  broken  brick  or  burned  clay  balls;  chlorine  gas 
and  steam  are  introduced  at  the  bottom  of  the  tower,  and  rising 
between  the  balls,  meet  descending  streams  of  hot  bittern.  By  reac- 
tion between  the  chlorine  and  the  magnesium  bromide,  the  bromine 
is  set  free.  The  chlorine  stream  must  be  regular,  and  so  controlled 
that  no  excess  is  used;  otherwise  some  bromine  chloride  is  formed. 
Part  of  the  bromine  dissolves  in  the  liquor  as  soon  as  set  free,  and 
this  liquor  flows  into  a  special  receiver,  heated  by  steam ;  here  it  is 
boiled  to  drive  out  the  bromine,  which,  together  with  water  vapor, 
passes  back  into  the  tower,  entering  at  the  bottom,  and  mixing  with 
the  chlorine.  At  the  top  of  the  tower,  the  bromine  vapor  passes  out 
into  an  earthenware  worm-condenser,  which  empties  into  a  closed 
vessel.  An  outlet  pipe  from  the  top  of  this  receiver  passes  into 
a  small  tower,  filled  with  moist  iron  turnings  or  scrap  iron.  Any 
uncondensed  vapors  of  bromine,  passing  out  of  the  receiver,  combine 
with  the  iron  to  form  ferrous  bromide,  which  is  used  for  making 
potassium  bromide. 

In  this  process,  any  bromine  chloride  formed  in  the  tower  is  decom- 
posed, before  it  can  pass  into  the  condensing  worm,  by  the  fresh 

249 


250  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

bittern  entering  at  the  top  of  the  tower.  Bromine  chloride  is  a  vol- 
atile liquid,  and  would  contaminate  the  bromine.  The  exhausted 
bittern  from  the  heating-vessel  goes  to  waste.  The  chlorine  gas 
necessary  is  made  in  special  stills  from  manganese  binoxide  and  hydro- 
chloric acid. 

The  periodic  process  depends  on  the  following  reaction :  — 

MgBr2  +  2  H2SO4  +  MnO2  =  MgSO4  +  MnSO4  +  2  H2O  +  2  Br. 

This  is  carried  on  in  sandstone  stills,  heated  by  steam.  A  charge 
of  pyrolusite,  sufficient  for  several  days,  is  put  into  the  still,  and 
the  bittern,  heated  to  60°  C.,  is  run  in.  The  quantity  of  sulphuric 
acid  to  be  added  is  carefully  gauged  with  each  charge  of  bittern  in 
order  that  none  of  the  magnesium  chloride  shall  be  decomposed. 
Usually,  a  little  of  the  magnesium  bromide  is  left  in  the  bittern, 
since  the  high  temperature  necessary  to  decompose  the  last  traces 
would  also  decompose  some  of  the  chloride,  which  would  form  bro- 
mine chloride,  and  contaminate  the  product.  The  bromine  distils 
over  into  a  condensing  worm,  as  above  described.  The  exhausted 
bittern  is  drawn  off  after  each  charge,  and  goes  to  waste.  At  the 
present  time,  considerable  potassium  chlorate  is  used  instead  of 
pyrolusite  for  the  oxidizing  agent.  This  is  especially  advantageous 
if  the  bittern  contains  much  calcium  chloride,  since  only  one-half  as 
much  sulphuric  acid  is  necessary,  and  there  is,  consequently,  less 
difficulty  from  calcium  sulphate.  Neither  the  stills  nor  the  tower 
should  be  lined  with  pitch  or  tar,  since  these  substances  absorb  much 
bromine. 

The  crude  bromine  obtained  by  either  process  contains  some  bro- 
mine chloride,  lead  bromide  from  the  pipe-joints  and  connections, 
and  some  organic  matter.  It  is  purified  by  shaking  with  ferrous, 
sodium,  or  potassium  bromide,  and  redistilling  from  glass  retorts. 
The  bromine  chloride  is  thus  decomposed,  and  the  salts  of  the  heavy 
metals  remain  in  the  still.  Very  pure  bromine  is  obtained  by  neu- 
tralizing with  barium  hydroxide  solution,  evaporating  to  dryness,  and 
calcining  at  a  red  heat.  The  barium  bromate  and  chlorate  formed  in 
the  neutralizing  are  decomposed  to  form  barium  bromide  and  chlo- 
ride. By  extracting  the  mass  with  alcohol,  the  bromide  is  dissolved. 
The  barium  bromide  obtained  by  evaporation  of  the  alcohol  is  de- 
composed with  pyrolusite  and  sulphuric  acid,  the  pure  bromine 
passing  to  the  condenser  as  vapor. 

Operations  with  liquid  bromine  must  be  carried  on  in  the  open 
air,  or  in  a  strong  draught.  If  inhaled,  the  vapors  are  suffocating, 


BROMINE  251 

and  cause  great  irritation  of  the  air  passages.  The  liquid  attacks 
the  skin,  and  causes  sores  which  heal  very  slowly. 

Bromine  is  largely  used  in  making  certain  coal-tar  dyes,  such 
as  the  eosins ;  for  sodium  and  potassium  bromides ;  and  to  some 
extent  as  a  chemical  reagent,  and  for  making  organic  bromides.  It 
is  considered  dangerous  freight  by  transportation  companies,  and  so 
only  its  salts,  especially  potassium  bromide,  are  usually  shipped. 

"  Solidified  bromine  "  is  a  convenient  form  for  laboratory  work. 
This  consists  of  sticks  of  diatomaceous  earth,  pressed  with  size  or 
molasses,  burned  till  coherent,  and  soaked  in  liquid  bromine.  The 
porous  material  absorbs  from  50  to  75  per  cent  of  its  weight  of  the 
liquid. 

Potassium  bromide  is  made  by  decomposing  iron  bromide  with 
potassium  carbonate.  The  ferroso-ferric  bromide  (Fe3Br8),  made  by 
adding  more  bromine  to  ferrous  bromide,  is  usually  employed. 

Fe  +  Br2  =  FeBr2. 

3  FeBr2  +  2  Br  =  Fe3Br8. 

Fe3Br8  +  4  K2CO3  +  4  H2O  =  Fe3(OH)8  +  8  KBr  +  4  CO2. 

The  solution  is  filtered  and  evaporated,  yielding  cubical  crystals  of 
the  salt,  free  from  bromate,  which  is  always  formed  when  bromine 
is  neutralized  directly  with  alkali. 

Potassium  bromide  is  used  in  medicine  and  in  photography,  espe- 
cially in  the  preparation  of  silver  bromide  plates  and  films. 

Sodium  bromide  is  similar  to  the  potassium  salt,  is  used  for  the 
same  purposes,  and  is  made  in  the  same  way ;  but  it  does  not  crystal- 
lize so  well. 

REFERENCES 

Berichte  iiber  die  Entwickelung  der  chemischen  Industrie.  —  A.  W.  Hof- 

mann,  1875,  129. 

Moniteur  scientifique,  1879,  905.  —  H.  S.  Welcome. 

Handbuch  der  Kali-Industrie,  E.  Pfeiffer,  321.  Braunschweig,  1887. 
Die  Gewinmmg  des  Broms  in  der  Kaliindustrie.  M.  Mitreiter,  Halle, 

a.  S.,  1910. 

Salt  Deposits  in  Ohio.    Bull.  8,  vol.  IX  (1906),  Rep't.  Ohio  Geol.  Survey. 
J.  A.  Bownocker. 


IODINE 

Iodine  is  obtained  from  the  ashes  of  seaweed,  and  from  the  mother- 
liquors  of  the  Chili  saltpetre  industry. 

Along  the  coasts  of  France,  Scotland,  and  Norway,  seaweed  is 
collected  and  burned  *  at  as  low  a  temperature  as  possible.  The  ash, 
called  kelp,  or  varec,  contains  from  0.5  to  1.5  per  cent  of  its  weight 
of  iodides  of  sodium  and  potassium.  It  is  lixiviated,  and  the  filtered 
solution  is  systematically  evaporated.  First,  sodium  sulphate,  and 
then  common  salt,  crystallizes.  By  further  evaporation,  sodium 
carbonate,  together  with  more  salt  and  potassium  chloride,  sepa- 
rates. The  mother-liquor  is  then  treated  with  sulphuric  acid  to 
decompose  the  alkali  sulphides  and  sulphites  formed  by  reduction  of 
the  sulphates  during  incineration.  This  precipitates  sulphur,  and 
the  sodium  sulphate  formed  crystallizes.  The  mother-liquor,  still 
holding  the  iodides  in  solution,  is  then  heated  to  60°  C.  in  iron  re- 
torts with  lead  covers,  and  having  pipes  leading  to  condensers.! 
Small  quantities  of  pyrolusite  are  introduced  into  the  retort  period- 
ically, when  the  following  reaction  takes  place :  — 

2  Nal  +  3  H2S04  +  MnO2  =  MnSO4  +  2  NaHSO4  +  2  H2O  +  I2. 

Pyrolusite  is  added  as  long  as  iodine  distils  off ;  but  excess  must 
be  avoided,  lest  bromine  and  chlorine  be  set  free  from  the  salts  still 
present  in  the  liquor,  and  combine  with  the  iodine  to  form  tribrom- 
or  trichlor-iodine  (IC13). 

Sometimes  the  iodine  liquor  is  decomposed  by  leading  chlorine 
gas  into  it,  the  same  as  in  making  bromine  (p.  249).  The  crude 
iodine  precipitates  as  a  paste,  and  is  washed  and  then  dried  on  porous 
plates.  Much  care  is  necessary  to  avoid  an  excess  of  chlorine,  since 
this  forms  volatile  iodine  trichloride  (IC13),  and  causes  loss. 

By  heating  the  acidified  iodide  solution  with   ferric  chloride  or 

*  By  burning  the  seaweed  in  closed  retorts,  the  loss  of  iodine  by  volatilization  is 
reduced. 

t  The  condensers,  called  udells,  are  bottle-shaped  vessels  of  earthenware,  ar- 
ranged horizontally,  5  or  6  in  a  series,  the  neck  of  one  entering  the  bottom  of  the 
next.  In  the  lower  side  of  each  is  a  small  hole,  through  which  the  condensed  water 
drains  off.  Each  still  has  two  sets  of  udells,  which  are  left  in  position  during  re- 
peated charges  of  the  still,  until  they  are  filled  with  solidified  iodine.  Recently 
the  condensers  have  been  made  of  seven  or  eight  lengths  of  plain  earthenware  pipe, 
each  length  3  feet  long  by  1|  feet  in  diameter,  and  the  joints  luted  with  clay. 

252 


IODINE  253 

potassium   chlorate,   the   iodine    is   liberated,   and    distils   off,   with 
some  water,  and  no  trichloride  is  formed,  thus :  — 

a)  2  Nal  +  2  FeCl3  =  2  FeCl2  +  2  NaCl  +  I2. 

6)  6  Nal  +  KC103  +  3  H2O  =  6  NaOH  +  KC1  +  6  I. 

Another  method  is  to  mix  the  kelp  with  a  little  water  and  sul- 
phuric acid,  and  to  add  potassium  bichromate :  — 

6  Nal  +  10  H2SO4  +  K2Cr2O7  =  6  NaHSO4  +  K2Cr2(SO4)4  +  7  H2O+  6 1. 

The  precipitated  iodine  is  washed,  dried,  and  sublimed. 

It  has  been  proposed  to  heat  the  kelp  directly  with  powdered 
bichromate,  decomposition  taking  place  at  a  red  heat,  and  the  iodine 
subliming :  — 

6  KI  +  K2Cr2O7  =  4  K2O  +  Cr2O3  +  61. 

The  seaweeds  of  the  Pacific  coast  of  America  may  also  furnish 
iodine  in  large  quantity,  when  the  market  conditions  will  warrant  its 
recovery. 

The  recovery  of  iodine  from  the  mother-liquors  of  Chili  saltpetre 
is  now  most  important.  The  iodine  is  chiefly  in  the  form  of  sodium 
iodate  (NalOs),  and  the  process  depends  on  the  following  reaction :  — 

2  NaIO3  +  5  SO2  +  4  H2O  =  Na2SO4  +  4  H2SO4  +  I2. 

In  practice,  the  sulphur  dioxide  is  used  in  the  form  of  sodium 
bisulphite  solution,  containing  some  neutral  sulphite.  This  is  made 
immediately  before  use  by  leading  sulphur  dioxide  gas  into  sodium 
carbonate  solution  until  the  liquid  contains  one  part  of  neutral  sul- 
phite to  two  of  acid  sulphite.  The  requisite  quantity  of  this  acid 
sulphite  liquor  is  added  to  the  mother-liquor,  and  thoroughly  agi- 
tated; the  precipitated  iodine  is  collected  on  filters  made  of  coarse 
bagging  or  canvas,  and  after  washing  is  pressed  heavily  to  remove 
excess  of  water.  The  reaction  is  probably  as  follows :  — 

2  NaIO3  +  3  Na2SO3  +  2  NaHSO3  =  5  Na2SO4  +  I2  +  H2O. 

But  since  some  sodium  iodide  is  also  present,  the  excess  of  bisul- 
phate  employed  decomposes  it  according  to  the  reaction :  — 

NaI03  +  Nal  +  2  NaHSO3  =  2  Na2SO4  +  I2  +  H2O. 

Sometimes  the  iodine  is  precipitated  as  cuprous  iodide  (Cu2I2)  by 
adding  copper  sulphate  and  sodium  bisulphite  to  the  mother-liquors, 


254  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

but  this  is  now  less  frequently  done  than  formerly.  The  cuprous 
iodide  was  shipped  to  Europe,  and  used  to  make  potassium  iodide 
by  treating  with  potassium  carbonate. 

The  liquors  from  which  the  iodine  has  been  separated  are  re- 
turned to  the  lixiviation  tanks  for  the  treatment  of  the  crude  "  caliche  " 
(p.  145). 

The  crude  iodine  obtained  by  any  of  the  above  processes  is  puri- 
fied by  resubliming  in  iron  retorts,  the  vapors  being  condensed  in 
earthenware  receivers.  The  temperature  of  the  retorts  must  be  very 
low  in  order  to  form  large  crystals,  and  the  condensers  must  not  be 
so  cool  as  to  cause  sudden  condensation  of  the  vapors. 

The  chief  uses  of  iodine  are  in  the  manufacture  of  coal-tar  dyes 
and  organic  compounds,  and  in  medicinal  preparations. 

The  most  important  iodine  derivative  is  potassium  iodide  (KI). 
This  is  made  in  several  ways  :  — 

(a)  Iodine  may  be  dissolved  in  a  caustic  potash  or  carbonate 
solution,  the  solution  evaporated  to  dryness,  and  the  mixture  of 
iodide  and  iodate  so  obtained  calcined  with  powdered  charcoal  at  a 
low  red  heat,  to  decompose  the  latter  salt. 

61  +  6  KOH  =  5  KI  +  KIO3  +  3  H2O. 
2  KI03  +  3  C  =  2  KI  +  3 


The  calcined  mass  is  lixiviated,  filtered,  and  crystallized.  Very  pure 
materials  are  needed  in  this  process. 

(b)  A  better  method  is  to  form  ferroso-ferric  iodide,  and  decom- 
pose  this  with   pure   potassium   carbonate.     Metallic   iron   is   dis- 
solved by  digesting  with  iodine  and  water,  forming  ferrous  iodide, 
which  is  then  treated  with  sufficient  iodine  to  form  the  ferroso- 
ferric  salt  :  — 

Fe  +  2  I  =  FeI2. 

3  Fel2  +  21  =  Fe3I8. 

Fe3I8  +  4  K2CO3  +  4  H2O  =  Fe3(OH)8  +  8  KI  +  4  CO2. 

This  method,  if  carefully  worked,  yields  a  very  pure  salt,  entirely 
free  from  potassium  iodate.  The  precipitated  ferroso-ferric  hydrox- 
ide is  granular,  and  more  easily  washed  than  is  ferrous  hydroxide. 

(c)  Barium  iodide  is  made  by  agitating  barium  sulphide  solution 
with  iodine.     The  clear  solution  is  then  boiled  with  potassium  sul- 
phate solution,  the  precipitated  barium  sulphate  filtered  off,  and  the 
filtrate  evaporated  until  the  potassium  iodide  crystallizes  :  — 


IODINE  255 

I2  =  BaI2+S. 
BaI2  +  K2SO4  =  BaSO4  +  2  KI. 

Potassium  iodide  is  chiefly  used  in  medicine  as  an  alterative  and 
diuretic.  A  small  quantity  is  used  in  photography. 

Lead,  mercury,  and  ferrous  iodides  are  used  to  a  small  extent  in 
medicine,  but  these  are  not  important. 

REFERENCES 

Wagner's  Jahresbericht  uber  die  Leistungen  der  chemischen  Technolo- 

S'e,  1879, 334.     E.  Sobering.  (Jodkalium.)     337.     G.  Langbein.  (Jod- 
ewinnung  in  Chili.) 
Journal  of  the  Society  of  Chemical  Industry :  — 

1893,  128.     J.  Buchanan.     (Extraction  of  Iodine  in  Chili.) 


PHOSPHORUS 

The  discovery  of  phosphorus,  about  1675,  is  attributed  to  an 
alchemist,  Brand,  at  Hamburg.  Urine  which  had  been  evaporated 
to  a  thick  syrup  was  heated  in  an  earthenware  retort  with  sand,  the 
phosphorus  distilling  off.  It  was  known  only  as  a  chemical  curios- 
ity until  Scheele,  in  1775,  made  it  from  bone-ash ;  soon  after  it  as- 
sumed commercial  importance.  Bone-ash  is  still  a  leading  source, 
but  the  mineral  phosphates,  being  cheaper,  are  now  used. 

Normal  calcium  phosphate  [Ca3(PO4)2]  is  reduced  by  carbon 
only  at  excessively  high  temperatures,  and  then  forms  calcium  phos- 
phide rather  than  the  free  phosphorus.  Free  phosphoric  acid  is,  how- 
ever, reduced  to  phosphorus.  In  the  old  process,  tricalcium  phos- 
phate (as  bone-ash)  was  decomposed  with  sulphuric  acid  to  form 
monocalcium  phosphate  and  calcium  sulphate.  By  leaching  with  hot 
water,  the  monocalcium  phosphate  was  dissolved,  and  the  solution, 
after  decantation  from  the  sulphate,  was  evaporated  in  lead  pans, 
when  powdered  charcoal  or  coke  was  stirred  in,  and  the  mass  heated 
in  iron  pans  until  dry.  The  dry  mixture  was  charged  into  earthen- 
ware retorts  and  heated  moderately  at  first,  and  then  to  very  high 
temperatures.  The  moderate  heating  reduced  the  monocalcium  phos- 
phate to  calcium  metaphosphate,  which  in  turn  was  decomposed  by 
the  carbon,  forming  tricalcium  phosphate,  phosphorus,  and  carbon 
monoxide.  The  reactions  were  as  follows :  — 

Ca3(PO4)2  +  2  H2SO4  =  CaH4(PO4)2  +  2  CaSO4. 

CaH4(P04)2  =  2  H2O  +  Ca(PO3)2. 

3  Ca(PO3)2  +  10  C  =  Ca3(PO4)2  +  P4  +  10  CO. 

This  left  one-third  of  the  phosphorus  combined  with  the  calcium, 
but  by  adding  silica  to  the  mixture,  all  of  the  phosphorus  is  liberated, 
according  to  the  reactions  :  — 

Ca(PO3)2  +  5  C  +  SiO2  =  CaSiO3  +  2  P  +  5  CO. 
Ca3(PO4)2  +  5  C  +  3  SiO2  =  3  CaSiO3  +  2  P  +  5  CO. 

The  electric  furnace  process  of  Headman,*  Parker,  and  Robinson, 
for  the  direct  reduction  of  calcium  phosphates  in  a  continuous-acting 

*  J.  Soc.  Chem.  Ind.,  1891,  445.     U.  S.  Pat.  No.  482,586  (1892). 
256 


PHOSPHORUS 


257 


FIG.  88. 


furnace  (Fig.  88)  ha?  now  replaced  the  older  methods.  The  retorts 
employed  in  the  old  process,  to  withstand  the  chemical  action  of  the 
charge,  had  to  be  made  from  materials 
which  are  poor  conductors  of  heat,  and  hence 
the  wear  and  tear  was  heavy,  and  the  heat 
efficiency  low.  Electrical  heating  develops 
the  energy  within  the  retort  itself,  and 
allows  the  retort  walls  to  be  kept  rela- 
tively cool.  Owing  to  the  high  tempera- 
ture attained  by  this  method  of  heating, 
silica  (as  sand)  may  be  introduced  directly 
in  the  charge,  all  of  the  phosphorus  being 
set  free  to  distil  out  of  the  furnace,  while 
a  fused  slag  is  separated  and  tapped  off  at  the  base  of  the  furnace. 

An  intimate  mixture  of  carbon,  phosphate,  and  flux  is  heated  ;  the 
gases  and  phosphorus  vapors  pass  by  the  pipe  (P),  to  the  condenser, 
while  slag  is  tapped  off  at  intervals,  through  (0).  Fresh  charges 
are  introduced  through  (H),  by  the  conveyer  (C).  The  carbon 
electrodes  (E)  are  in  metal  sockets  passing  through  the  walls  of  the 
furnace.  The  working  holes  (X)  are  closed  with  clay  when  the  fur- 
nace is  running.  This  method  avoids  the  use  of  sulphuric  acid,  the 
concentration  and  handling  of  phosphoric  acid,  uses  no  earthenware 
retorts,  and  saves  time ;  it  is  further  claimed  that  less  coke  is  used. 

The  crude  phosphorus  made  by  any  of  the  above  processes  con- 
tains sand,  carbon,  clay,  and  other  impurities.  It  is  purified  by 
melting  under  warm  water,  and  straining  through  canvas  bags ; 
formerly  chamois  leather  was  used.  Or  it  is  redistilled  from  iron 
retorts.  Sometimes  it  is  treated  with  a  3  per  cent  solution  of  potas- 
sium bichromate  and  its  equivalent  of  sulphuric  acid,  in  a  lead-lined 
agitator  which  is  heated  by  steam  coils.  After  a  couple  of  hours' 
agitation,  the  phosphorus  is  nearly  transparent,  and  of  a  light  yel- 
low color.  It  is  washed  with  hot  water,  filtered  through  canvas 
bags,  and  moulded  into  "  sticks  "  by  pouring  into  glass  or  tin  tubes 
placed  in  cold  water.  For  shipment,  phosphorus  is  packed  in  water 
in  tin  boxes,  the  lids  of  which  are  tightly  soldered. 

Yellow  or  ordinary  phosphorus  is  a  pale  yellow,  translucent,  wax- 
like  mass  of  1.82  specific  gravity,  very  inflammable,  and  combining 
directly  with  oxygen,  sulphur,  and  the  halogens.  It  melts  at  43.3° 
C.  under  water,  and  at  30°  C.  when  dry;  it  distils  at  269°.*  It  is 
very  soluble  in  carbon  disulphide,  sulphur  chloride,  and  phosphorus 

*  J.  B.  Readman,  Thorpe's  Dictionary  of  Applied  Chemistry,  Vol.  IV.,  205. 

s 


258  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

trichloride,  slightly  so  in  caustic  soda  solution,  but  insoluble  in 
water.  It  is  exceedingly  poisonous,  less  than  0.15  gram  being  a 
fatal  dose.  Persons  working  continuously  with  yellow  phosphorus 
are  subject  to  necrosis,  usually  appearing  first  in  the  jawbones. 

The  chief  uses  of  yellow  phosphorus  are  in  making  matches  and 
phosphor-bronze,  and  for  rat  poison. 

Amorphous  or  red  phosphorus  is  made  by  heating  the  yellow 
variety  for  several  hours  in  closed  retorts  at  250°  C.  If  an  auto- 
clave be  employed,  and  the  temperature  raised  to  300°  C.,  the  press- 
ure inside  the  vessel  makes  the  process  much  more  rapid.  The 
hard  mass  thus  produced  is  ground  under  water,  and  the  powder 
boiled  with  caustic  soda  solution  to  remove  any  unchanged  yellow 
phosphorus.  Carbon  disulphide  is  sometimes  used  instead  of  caus- 
tic soda,  but  this  is  expensive  and  easily  inflamed.  After  boiling  in 
water,  filtering,  and  drying  by  steam  heat,  the  amorphous  phospho- 
rus is  packed  dry."  Red  phosphorus  is  a  reddish  brown,  opaque 
substance,  having  a  specific  gravity  of  2.25.  It  is  not  affected  by 
heating  in  the  air  until  the  temperature  reaches  260°  C.,  at  which 
point  it  inflames.  By  heating  in  an  atmosphere  of  nitrogen  or  car- 
bon dioxide,  it  distils,  returning  to  the  yellow  variety.  It  is  insol- 
uble in  carbon  disulphide,  caustic  soda,  and  in  water,  and  is  not 
poisonous.  The  chief  use  of  red  phosphorus  is  in  the  manufacture 
of  "  safety  matches." 

MATCHES 

In  about  1812,  the  so-called  "chemical  matches  "  were  invented. 
Sticks  were  dipped  in  melted  sulphur,  and  the  "head  "  coated  with 
a  mixture  of  sugar  and  potassium  chlorate.  It  was  fired  by  dipping 
into  a  bottle  containing  asbestos  moistened  with  sulphuric  acid. 

Friction,  or  lucifer,  matches  were  invented  in  1827,  in  England. 
The  heads  were  a  mixture  of  antimony  trisulphide  and  potassium 
chlorate,  made  into  a  stiff  paste  with  water  and  gum.  They  were 
ignited  by  rubbing  on  sand  or  emery  paper.  The  antimony  trisul- 
phide was  soon  replaced  by  phosphorus,  and  the  potassium  chlorate 
by  nitre.  At  the  present  time,  lead  peroxide,  red  lead,  or  man- 
ganese dioxide  are  used  instead  of  nitre  as  the  oxidizing  substance. 
Chlorates  are  used;  but  sparingly,  since  they  form  explosive  mixtures. 

Soft  wood,  generally  pine  or  spruce,  is  cut  by  machines  to  form 
the  sticks,  which  are  thoroughly  kiln-dried.  They  are  then  fixed  in 
a  frame  so  that  each  stick  stands  alone,  and  the  end  of  each  stick  is 
well  soaked  in  melted  sulphur,  paraffine,  or  stearic  acid.  The  igniting 


PHOSPHORUS 


259 


mixture  is  made  by  ,slowly  stirring  phosphorus  into  a  warm  solution 
of  dextrine  or  glue ;  the  oxidizing  materials  are  then  added,  and  the 
paste  stirred  until  cold.  It  is  frequently  colored  with  ultramarine, 
lead  chromate,  chalk,  or  lampblack.  It  is  then  spread  evenly  in  a 
thin  layer  on  a  table,  and  the  prepared  sticks  dipped  into  it  once  or 
twice.  After  drying,  the  heads  are  sometimes  dipped  in  thin  shel- 
lac or  other  varnish,  to  protect  them  from  the  moisture  in  the  air. 

Safety  matches  are  made  without  yellow  phosphorus.  The  match 
head  is  generally  sulphur,  or  antimony  trisulphide,  with  potassium  chlo- 
rate, or  bichromate,  as  the  oxidizing  material.  Sometimes  red  lead,  lead 
peroxide,  or  manganese  dioxide  is  used  as  a  part  of  the  oxidizing  mate- 
rial. The  surface  upon  which  the  match  must  be  lighted  is  coated  with 
a  mixture  of  red  phosphorus,  antimony  trisulphide,  and  dextrine,  or 
glue.  Powdered  glass  or  emery  is  used  to  increase  the  friction. 

The  compositions  used  on  matches  are  carefully  guarded  as  trade 
secrets,  and  are  different  in  different  factories.  One  is  given  as 
follows :  — 


HEAD  COMPOSITION 

KC1O3 5  parts 

K2Cr2O7 2  parts 

Glass  Powder      ....  3  parts 

Gum 2  parts 


RUBBING  SURFACE 

Sb2S3 5    parts 

Red  Phosphorus    ...  3    parts 

MnO2 1£  parts 

Glue 4    parts 


The  friction  of  the  match  head  on  the  prepared  surface  develops 
sufficient  heat  to  convert  a  little  of  the  red  phosphorus  to  the  yellow 
variety,  which  at  once  combines  with  some  of  the  potassium  chlorate 
and  antimony  sulphide,  evolving  enough  heat  to  inflame  the  mix- 
ture on  the  head. 

To  prevent  the  burned  stems  from  smouldering,  the  sticks  are 
sometimes  soaked  in  a  solution  of  magnesium  sulphate,  alum,  or 
sodium  phosphate  before  making  the  head. 

In  some  countries,  e.g.  Switzerland,  the  manufacture  and  sale  of 
matches  containing  yellow  phosphorus  is  prohibited.  .  In  this  country 
their  production  has  been  eliminated  by  the  imposition  of  a  prohib- 
itive tax  of  1  cent  per  100  matches. 


REFERENCES 

Chemical  News,   1879,   147.     J.  B.  Readman.     (Manufacture  of  Phos- 
phorus.) 

Chemiker-Zeitung,  1881, 196.    A.  Rossel.     (Matches  without  Phosphorus.) 
Journal  of  the  Society  of  Chemical  Industry :  — 

1890,  163,  473.     J.  B.  Readman.     (Manufacture  of  Phosphorus.) 

1891,  445.     J.  B.  Readman.     (Manufacture  of  Phosphorus.) 


BORIC  ACID 

Boric  acid  [B(OH)3]  occurs  in  volcanic  regions,  especially  in  Tus- 
cany, as  a  constituent  of  the  vapors,  called  soffioni,  which  escape 
from  hot  springs  and  from  openings  in  the  ground,  called  fumeroles. 
In  some  places  the  water  has  evaporated  from  the  fumeroles,  and  the 
boric  acid  has  crystallized,  forming  the  mineral  sassolite.  Combina- 
tions of  boric  acid  with  sodium,  magnesium,  and  calcium  are  found 
in  various  places :  as,  tinkal  (native  borax),  Na2B4O7  •  10  H2O ;  bora- 
cite,  2(Mg3B8Oi5),  MgCl2 ;  borocalcite,  CaB4O7  •  6  H2O ;  and  borona- 
trocalcite  (ulexite),  Na2B4O7,  (2  CaB4O7),  18  H2O. 

In  Tuscany,  natural  or  artificial  ponds  (lagoons)  are  formed 
around  the  fumeroles,  or  a  series  of  masonry  basins  or  tanks  are 
constructed  over  them,  and  the  soffioni  made  to  bubble  through 
water  in  these,  thus  washing  most  of  the  boric  acid  from  the  vapors. 
These  tanks  are  so  arranged  that  the  water  from  one  flows  into  an- 
other at  a  lower  level;  in  the  final  basin,  a  solution  containing  about 
2  per  cent  boric  acid  is  obtained.  The  solution  is  evaporated,  either 
in  lead-lined  vessels,  heated  by  the  steam  from  the  fumeroles,  or  in 
cement-lined  tanks,  having  coils  through  which  the  steam  passes. 
Calcium  sulphate  deposits  freely  during  the  evaporation  of  the 
solution,  which  is  concentrated  to  1.08  specific  gravity.  It  is  then 
crystallized  in  lead-lined  wooden  vats.  The  crystals  are  drained 
for  some  hours,  and  dried  on  a  floor  also  heated  by  steam  from  the* 
fumeroles.  The  crude  boric  acid  is  purified  by  recrystallization.  In 
many  places  in  Tuscany,  bored  wells  are  sunk  from  200  to  300  feet, 
and  the  vapors  escape  from  these  as  from  the  natural  fumeroles. 

Boric  acid  is  made  in  California,  and  in  Chili,  by  boiling  calcium 
borates,  suspended  in  water,  with  sulphur  or  sulphurous  acid :  — 

Ca2B6On  •  5  H2O  +  8  S  +  10  H2O  =  2  CaSO4  +  6  B(OH)3  +  6  H2S. 
CasBAi  •  5  H20  +  4  SO2  +  6  H2O  =  6  B(OH)3  +  2  Ca(HSO3)2. 

Much  boric  acid  is  made  from  the  boracite  in  the  Stassfurt  salts. 
The  mineral  is  crushed,  and  treated  with  just  enough  hydrochloric 
acid  to  decompose  it.  A  rather  vigorous  reaction  takes  place,  and 
the  mass  becomes  pasty.  It  is  dissolved  in  boiling  water,  and  care- 
fully tested  for  free  hydrochloric  acid;  if  none  is  present,  the  solu- 
tion of  boric  acid  is  decanted  from  the  sediment  of  clay  and  sand,  or 

260 


BORIC  ACID  261 

filtered  through  linen  bags,  and  is  crystallized  in  lead-lined  or  iron 
tanks.*  Sulphuric  acid  is  also  used  to  decompose  the  boracite,  in 
which  case  the  mother-liquors  from  the  boric  acid  contain  magne- 
sium sulphate;  this  is  recovered  as  Epsom  salt.  The  following 
reactions  are  involved :  — 

1)  (2  Mg3B8Oi5),  MgCl2  +  12  HC1  +.  18  H2O  =  7  MgCl2  +  16  B(OH)3. 

2)  (2  Mg3B8015),  MgCl2  +  7  H2SO4  +  18  H2O  = 

7  MgSO4  +  2  HC1  +  16  B(OH)3. 

The  actual  quantity  of  acid  used  is  determined  for  each  lot  of  salt. 

Boric  acid  forms  pearly  white,  laminated  crystals,  very  slightly 
soluble  in  cold  water,  but  dissolving  readily  in  hot  water.  It  has 
but  little  taste.  When  heated,  it  loses  water,  and  at  140°  C.  forms 
pyroboric  acid  (H2B4O7).  At  a  red  heat,  all  the  water  is  expelled, 
and  boric  anhydride  (B2O3)  results;  this  is  stable  and  non- volatile, 
even  at  high  temperatures.  Consequently,  it  will  decompose  nearly 
all  metallic  sulphates,  carbonates,  and  nitrates  when  fused  with 
them,  forming  metallic  borates.  Hence  it  is  used  as  a  flux.  Boric 
acid  is  chiefly  used  in  the  preparation  of  borax;  in  enamels  and 
glazes  for  pottery ;  in  making  Guignet's  green ;  as  an  antiseptic  in 
medicine  and  surgery ;  and  for  preserving  fish,  meat,  and  milk. 

Borax,  sodium  biborate  (Na2B4O7),  is  the  only  important  salt  de- 
rived from  boric  acid.  It  is  found  native  in  Thibet,  Ceylon,  and 
California.  But  little  is  known  of  the  method  of  preparing  borax 
in  Thibet.  It  comes  from  that  country  as  tinkal,  an  impure,  crys- 
tallized borax,  containing  lime,  magnesia,  sulphates,  and  chlorides 
and  a  greasy  substance  added  presumably  to  protect  the  crystal 
from  efflorescence  and  breakage.  The  tinkal  is  purified  by  dissolv- 
ing in  hot  water,  and  adding  lime-water  and  calcium  chloride,  to  pre- 
cipitate the  grease  as  lime  soap.  After  filtering,  the  borax  is  crys- 
tallized by  concentrating  the  solution. 

Borax  was  formerly  obtained  by  evaporating  the  water  and  by 
washing  the  mud  from  the  beds  of  several  ponds  (Borax  Lake,  and 
others)  in  Lake,  Inyo,  Kern,  and  San  Bernardino  counties  in  Califor- 
nia ;  this  was  succeeded  by  its  recovery  from  various  dry  lake  beds, 
so-called  "  marshes,"  in  the  Death  Valley  region,  where  the  surface 
efflorescence,  or  crusts,  consists  of  a  mixture  of  borax,  soda,  salt,  and 
sulphate.  At  present  nearly  all  borax  produced  in  this  country  is  made 

*  F.  Wittig  (Zeit.  angew.  Chem.,  1888,  483),  recommends  iron  crystallizing 
tanks,  because  lead-lined  vessels  buckle  and  leak,  owing  to  the  changes  of  tempera- 
ture. The  iron  soon  becomes  polished,  and  yields  perfectly  clean  crystals. 


262  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

from  ulexite  or  "  cotton  ball  "  (NaCaB5O9  •  8  H2O)  and  colemanite 
(Ca2B6On  •  5  H2O),  found  in  Inyo,  San  Bernardino,  and  Ventura  coun- 
ties. 

The  ore  in  small  lumps  is  roasted  at  low  heat  in  a  rotary  furnace, 
to  expel  water  and  cause  the  colemanite  to  fall  to  powder,  which  is 
sifted  to  remove  the  refuse  calcite,  sand,  clay,  etc.  The  powder  is 
boiled  in  sodium  carbonate  and  bicarbonate  solution  until  decomposed, 
the  calcium  carbonate  settled,  and  the  brown  solution  of  borax  run 
into  large  iron  crystallizing  vats,  which  are  sheathed  with  wood  to 
prevent  too  rapid  cooling.  To  form  good  crystals,  the  solution  should 
cool  very  slowly,  and  the  vats  are  usually  covered  to  prevent  the  for- 
mation of  surface  crust.  Wires  are  suspended  in  the  vat  for  the  borax 
to  crystallize  upon,  which  requires  from  7  to  10  days.  Impure  crys- 
tals deposit  on  the  bottom  and  sides  of  the  vat,  and  are  generally 
recrystallized  from  water.  The  sodium  bicarbonate  is  added  to 
prevent  the  formation  of  metaborate.  The  reactions  are  as  follows  :  — 


5  H2O  +  2  Na2CO3  +  2  NaHCO3  = 

4  CaCO3  +  3  Na2B4O7  +  11  H2O. 
4  NaCaB5O9  •  8  H2O  +  2  Na2CO3  +  2  NaHCO3  = 

4  CaCO3  +  5  Na2B4O7  +  9  H2O. 

The  sludge  from  the  decomposing  vat  is  boiled  with  water,  filter- 
pressed,  and  the  liquor  sent  to  the  next  decomposing  operation,  while 
the  mud  is  thrown  away. 

A  borocalcite  called  pandermite,  found  in  Asia  Minor  and  some 
other  localities,  is  worked  in  somewhat  similar  manner. 

Much  of  the  boric  acid  produced  in  Italy  is  converted  to  borax 
by  boiling  it  with  sodium  carbonate  ;  the  solution  is  concentrated  to 
22°  Be.  at  104°  C.,  settled  and  run  into  shallow,  open,  crystallizing 
vats,  where  the  borax  deposits  within  three  days  ;  but  for  recrystal- 
lization  deep  tanks,  tightly  covered,  and  lagged  to  prevent  radiation 
of  heat,  are  used  ;  from  16  to  18  days  are  required,  and  large  crystals 
are  formed. 

Borax  comes  in  trade  in  two  forms  :  common  or  prismatic  borax 
(Na2B4O7  •  10  H2O),  and  octahedral  borax  (Na2B4O7  •  5  H2O).  The  for- 
mer is  produced  as  large,  "efflorescent,  monoclinic  crystals,  by  crystal- 
lizing from  a  solution  of  22°  Be.,  which  is  permitted  to  cool  to  27°  C.  ; 
it  melts  in  its  water  of  crystallization  when  heated,  then  swells  greatly, 
forming  a  spongy  mass,  which  fuses  at  red  heat  to  a  transparent  glass. 
Octahedral  borax  is  obtained  as  regular  octahedrons,  when  a  solution 


BORIC  ACID  263 

of  common  borax  is  concentrated  to  30°  Be.,  and  cooled  only  to 
56°  C.  It  is  permanent  in  dry  air,  but  absorbs  moisture  on  exposure, 
and  passes  into  the  prismatic  variety ;  it  fuses  without  intumescence, 
and  is  preferred  as  a  flux  for  brazing  and  soldering. 

Borax  is  used  as  a  flux  in  welding  and  brazing  metals ;  in  enamel 
and  glazes  for  metal  ware  and  pottery  ;  in  laundry  work  and  in  starch 
to  increase  the  gloss ;  in  soaps,  especially  those  intended  for  use  in 
hard  water ;  for  preserving  meat ;  as  a  mordant  in  dyeing ;  for  the 
ungumming  of  raw  silk ;  in  medicine  and  pharmacy ;  and  with  casein 
for  the  preparation  of  paste. 

Perborates,*  derivatives  of  the  acid  HBO3,  have  become  important 
industrially,  as  oxidizing  agents.  Sodium  perborate  (NaBO3  •  4  H2O), 
is  a  stable,  crystalline  salt,  produced  from  sodium  peroxide  and 
boric  acid  solutions ;  in  cold,  aqueous  solution  it  acts  like  hydrogen 
peroxide. 

REFERENCES 

Hofmann's  Bericht  iiber  die  Entwickelung  der  Chemischen  Industrie. 

1875,  324,  343. 

Handbuch  der  Kali-Industrie.  E.  Pfeiffer,  Braunschweig,  1887.  (Boracit.) 
Chemiker-Zeitung :  — 

1879,  46.     (Boric  Acid  from  Boracite.)     1887,  605.     (Borax  in  Chili.) 
Third  Annual  Report  of  the  California  State  Mineralogist,  1883. 
Die  Stassfurter  Kali-Industrie.     G.  Lierke,  Wien,  1891. 
California  State  Mining  Bureau,  Bui.  No.  24.     The  Saline  Deposits  of 

California,  1902. 
Zeitschrif  t  f  iir  angewandte  Chemie :  — 

1888,  483.     F.  Witting.      (Borax  from  Boronatrocalcite.)      1891,  367. 
1892,  241.     Dr.  Scheuer.     (Boric  Acid  and  Borax  Industry.) 

Journal  of  the  Society  of  Chemical  Industry :  — 

1889,  857.     C.  N.  Hake.     (Borax  Lake  in  California.)     1892,  683. 
Engineering  and  Mining  Journal :  — 

(Borax.)     53,  8.     54,  247. 

*  Compt  rendu,  1904  (139),  796.  J.  Soc.  Chem.  Ind.,  1904,  1145;  1905,  275, 
276,  332. 


ELECTRIC  FURNACE  PRODUCTS 

The  electric  furnace  *  is  used  for  one  or  more  of  the  following  rea- 
sons :  (a)  To  secure  temperatures  higher  than  are  attainable  with 
combustion  furnaces,  thus  making  possible  the  production  of  certain 
substances  previously  unknown,  or  obtained  with  great  difficulty; 
(6)  for  generating  heat  at  the  exact  point  required,  thus  avoiding 
the  heat  losses  and  depreciation  of  plant  incident  to  forcing  large 
quantities  of  heat  through  retaining  walls;  (c)  for  the  maintenance 
of  definite  conditions  (especially  reducing  atmosphere)  within  the 
container. 

The  successful  application  of  the  electric  furnace  to  technical 
uses  by  Messrs.  Cowles,  in  Cleveland,  Ohio,  in  1884,  was  the  begin- 
ning of  large  industries.  Various  modified  forms  of  the  Cowles  fur- 
nace are  now  used  to  produce  carborundum,  artificial  graphite, 
calcium  carbide,  phosphorus,  alundum,  barium  hydrate  and  cyanide, 
and  other  products,  and  in  metallurgical  operations. 

The  Cowles  furnace  (Fig.  89)  consists  of  a  crucible  (F),  into 
which  the  movable  electrodes  (E)  pass.  The  cover  has  an  opening 

(0)  for  the  escape  of  the  gases.  The 
carbon  electrodes  are  in  contact  at  first, 
but  are  slowly  separated  as  the  charge 
and  furnace  become  hot,  and  the  cur- 
rent passes  through  the  mixture  in  the 
crucible,  or  an  arc  is  formed.  At  (J) 
the  electrodes  are  joined  to  the  conduc- 
tors from  the  dynamos.  When  the  electrodes  have  been  separated 
until  the  ammeter  readings  have  become  nearly  constant,  the  opera- 
tion is  allowed  to  go  on  for  some  hours.  Either  direct  or  alternating 
currents  may  be  used,  when  the  desired  results  can  be  obtained  by  a 
high  temperature,  and  are  not  due  to  electrolysis. 

In  some  forms  of  electric  furnaces  the  heating  is  accomplished  by 
passing  the  current  through  a  conductor  of  relatively  high  resistance 
embedded  in  the  charge;  the  heat  from  the  resistance  warms  the 
adjacent  portions  of  the  charge. 

Carborundum,  or  silicon  carbide,  was  first  made  on  a  technical 

*  Electric  Furnaces  and  their  Industrial  Applications,  J.  Wright,  New  York, 
1905.  The  Electric  Furnace,  Alfred  Stansfield,  2d  Ed.,  New  York,  1914.  (Mc- 
Graw-Hill Co.)  Trans.  Faraday  Society,  Jan.  1905  (I),  85. 

264 


ELECTRIC   FURNACE   PRODUCTS  265 

scale  by  E.  G.  Acheson,  about  1891,  using  the  Cowles  furnace.  It  is 
now  extensively  produced  at  Niagara  and  other  places,  and  used  as 
an  abrasive,  replacing  emery  and  corundum.  The  charge  of  100 
parts  coke  powder,  100  parts  sand,  and  25  parts  common  salt,  to 
which  a  little  sawdust  is  sometimes  added,  is  packed  around  a  hori- 
zontal core,  twelve  feet  long,  of  granulated  coke,  joining  the  elec- 
trodes, which  are  embedded  in  the  furnace  walls.  The  heat  causes 
the  granulated  coke  to  sinter  together;  the  salt  causes  adhesion 
between  the  particles  of  the  charge.  As  the  reaction  proceeds, 
large  quantities  of  carbon  monoxide  are  evolved,  and  the  furnace  is 
enveloped  in  blue  flames.  The  reaction  is :  — 

SiO2  +  3  C  =  SiC  +  2  CO. 

After  several  hours  vapors  of  sodium  appear  and  cause  the  flame  to 
become  yellow ;  the  furnace  is  permitted  to  cool,  and  the  core  is  found 
surrounded  by  a  crust  of  crystallized  carborundum,  with  an  inter- 
vening layer  of  graphite,  formed  by  the  decomposition  of  some  of 
the  carborundum  by  the  heat.  The  brilliant  black  carborundum 
crystals  often  have  a  splendid  iridescent  lustre.  The  material  is 
sorted  by  hand,  and  the  carborundum  crushed  and  washed  with  sul- 
phuric acid  to  remove  traces  of  iron,  aluminum,  sulphides,  phosphides, 
carbides,  etc.  It  is  then  washed  with  water,  and  levigated  to  separate 
the  powder  into  commercial  sizes. 

Carborundum  is  not  attacked  by  acids  or  by  sulphur  fumes,  is 
stable  in  the  air  and  infusible,  and  is  harder  than  corundum.  It  is 
decomposed  by  fusion  with  caustic  alkalies  and  nitre,  and  is  attacked 
by  chlorine  above  600°  C. 

Artificial  graphite  is  made  by  heating  amorphous  carbon  in  the 
presence  of  ferric  oxide  or  silica,  at  high  temperature,  so  that  the  iron 
or  silicon  is  vaporized  and  the  carbon  is  left  in  the  crystalline  form 
as  graphite.  At  intermediate  temperatures  in  the  presence  of  carbon, 
iron  and  silicon  form  carbides ;  at  higher  temperatures,  the  carbides 
dissociate  into  the  elements  and  the  carbon  formed  by  the  dissociation 
is  in  the  form  of  graphite.  Thus  iron  and  silicon  act  as  catalyzers 
of  the  graphite  formation. 

The  brick  furnace  used  is  similar  to  the  carborundum  furnace 
and  has  carbon  electrodes.  Anthracite  coal,  as  raw  material,  is  filled 
into  the  furnace  around  a  carbon  rod  as  a  core  between  the  terminals, 
which  heats  the  coal  at  the  start  since  it  is  a  poor  conductor  of  heat 
when  cold.  Nearly  all  impurities  are  vaporized  and  the  graphite 
contains  only  about  0.5  per  cent  of  ash.  This  product  is  used  for 


266 


OUTLINES   OP   INDUSTRIAL   CHEMISTRY 


lubricators,  paints,  dry  batteries,  pencils,  etc.  Articles  formed 
from  pulverized  amorphous  carbon,  pressed  into  moulds,  can  be 
"  graphitized  "  in  the  electric  furnace  without  change  of  form. 

Calcium  carbide  was  first  prepared  on  a  commercial  scale  by 
T.  L.  Willson,  about  1895,  although  it  had  been  known  as  a  labo- 
ratory product  many  years  before. 

By  heating  an  intimate  mixture  of  pulverized  lime  and  coke  in 
an  electric  furnace,  calcium  carbide  is  formed  directly :  — 

CaO  +  3  C  =  CaC2  +  CO. 

The  furnace  (Fig.  90)  *  generally  used  is  made  of  fire-brick  and 
lined  with  carbon;  it  is  designed  for  3000  to  4000  kilowatts.  The 
iron  bottom  of  the  furnace  connects  with  the  carbon  lining  of  the 


FIG.  90. 

bottom,  to  form  one  electrode,  and  the  other  electrode  is  suspended 
so  that  it  hangs  free  within  the  hearth.  The  fused  carbide  forms  a 
pool  under  the  electrode,  which  is  raised  or  lowered  as  need  be  by  the 
hoist  (W).  The  furnace  is  tapped  at  intervals,  by  means  of  a  special 
arc,  -sprung  at  the  end  of  the  pointed,  tapping  electrode  (A),  by  which 
a  hole  can  be  melted  through  the  furnace  wall  in  a  few  minutes.  For 
a  short  time  previous  to  tapping,  no  fresh  charge  is  introduced  and 
the  fused  carbide  in  the  furnace  forms  a  thin,  liquid  bath.  The 
*  Electrochem.  Ind.,  1908  (7),  400. 


ELECTRIC   FURNACE    PRODUCTS  267 

charge  itself  serves  to  protect  the  fire-brick  walls  from  the  intense  heat 
of  the  arc. 

The  raw  materials,  which  must  not  contain  water,  phosphate,  sul- 
phate, nor  mangesia,  are  lime  or  limestone,  and  coke,  charcoal,  or 
anthracite;  these  are  coarsely  pulverized  and  mixed  in  proportions 
of  95  kg.  lime  to  68  kg.  coke.  In  theory,  to  produce  100  kg.  of  car- 
bide, 87.5  kg.  of  lime  and  56.25  kg.  of  carbon  are  needed.  One  kilo- 
gram of  carbide  requires  about  4  kilowatt-hours,  and  1  ton  of  carbide 
is  obtained  from  1.79  tons  of  mixture  of  lime  and  coke. 

Calcium  carbide  is  a  hard,  crystalline  mass,  with  lustrous  surface 
when  freshly  broken,  but  soon  tarnishing  and  decomposing  in  the 
air.  It  reacts  at  once  with  water,  forming  acetylene  and  calcium  hy- 
droxide :  — 

CaC2  +  2  H2O  =  C2H2  +  Ca(OH)2. 

Commerical  carbide  contains  about  80  per  cent  CaC2,  and  is  chiefly 
used  to  prepare  acetylene  gas  (p.  324),  for  the  manufacture  of  calcium 
cyanamide  (below),  and  somewhat  as  a  germicide  in  combating 
phylloxera. 

Calcium  cyanamid,*  discovered  by  Franlc  and  Caro  when  attempt- 
ing the  synthesis  of  cyanides  (p.  290),  is  formed  when  purified  and 
concentrated  nitrogen  gas  (from  liquid  air)  is  brought  into  contact 
with  finely  ground  calcium  carbide,  in  ovens  heated  to  about  1000°  C. 
The  reaction 

CaC2  +  N2  ^±  CaCN2  +  C 

is  reversible  if  the  conditions  are  not  kept  within  certain  limits,  re- 
garded as  trade  secrets. 

The  product  from  the  ovens  is  a  hard  cake  (black  from  the  free 
carbon),  with  about  22  per  cent  nitrogen  and  1  per  cent  carbide. 
After  fine  grinding  and  careful  hydration  of  the  residual  carbide,  the 
material  goes  to  the  fertilizer  trade  as  "  lime-nitrogen"  or  "  nitrolim." 
It  also  finds  use  in  making  synthetic  ammonia  (p.  150) ;  for  cyanides 
by  fusion  with  common  salt ;  and  for  case-hardening  iron,  especially 
for  armor  plate. 

Alundum  is  the  name  given  to  an  artificial  corundum  (A^Oa),  pro- 
duced by  fusing  bauxite  in  the  electric  arc  furnace.  Iron  and  most  other 
impurities  volatilize,  leaving  nearly  pure  aluminum  oxide  in  the  fur- 
nace. The  cooled  mass  is  pulverized  in  crushers  and  rolls,  and  sieved 
to  the  desired  size  of  grain,  for  making  into  wheels  and  other  imple- 

*  Zeitsch.  angew.  Chem.,  1903  (16),  536;  1910  (23),  2405.  J.  Soc.  Chem.  Ind., 
1903,  809.  Electrochem.  Met.  Ind.,  1907,  77  ;  1908,  341 ;  1910,  539  ;  1915,  213. 


268  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

ments  for  grinding  and  polishing,  and  for  refractory  linings  and  similar 
uses.  As  an  abrasive  it  is  harder  and  tougher  than  emery,  which  it 
has  largely  replaced. 

Barium  hydroxide  *  is  made  in  the  electric  furnace  from  barytes, 

thus :  — 

1)  4  BaSO4  +  4  C  =  3  BaSO4  +  BaS  +  4  CO. 

2)  3  BaSO4  +  BaS  =  4  BaO  +  4  SO2. 

A  mixture  of  ground  barytes  and  coke,  in  the  above  proportions, 
is  heated  in  an  electric  furnace  which  may  be  tapped  periodically. 
The  first  reaction  takes  place  at  once  and  at  moderate  temperature, 
but  the  second  is  slower  and  requires  very  high  heat.  The  product 
tapped  from  the  furnace  is  dissolved  in  hot  water,  and  the  solution 
of  hydroxide  and  sulphydrate  filtered.  Crystals  of  Ba(OH)2  •  8  H2O 
separate  from  the  solution  on  cooling,  the  sulphydrate  remaining  in 
the  mother-liquor.  The  crystals  are  centriffed,  washed,  and  dried. 
The  reduction  of  the  barytes  is  claimed  to  equal  nearly  97  per  cent 
of  the  available  sulphate,  and  the  product  is  very  pure. 

Cyanides  J  may  be  made  in  the  electric  furnace  by  heating  a  mix- 
ture of  barium  carbonate  ^,nd  coal  or  coke  dust  until  barium  carbide 
is  formed,  and  then  introducing  nitrogen  gas  (deoxidized  air),  whereby 
barium  cyanide  is  produced.  The  charge  is  cooled  somewhat  before 
the  nitrogen  is  brought  in  contact  with  the  mass. 

For  electric  carbon  disulphide  process,  see  p.  297. 

For  electric  phosphorus  process,  see  p.  256. 

REFERENCES 

Applied  Electrochemistry.    By  M.  de  Kay  Thompson,  New  York,  1911. 
(Macmillan  Co.) 

*  J.  Soc.  Chem.  Ind.,  1902,  391.     Trans.  Am.  Inst.  Elec.  Eng.,  1902. 
f  J.  Soc.  Chem.  Ind.,  1900,  745.     U.S.  Pat.  Nos.  657,937 ;  657,938. 


ARSENIC  COMPOUNDS 

Arsenious  acid,  white  arsenic,  or  arsenic  trioxide  (A^Oa)  is  the 
most  important  arsenic  derivative.  It  is  made  by  roasting  arsenical 
pyrites  (mispickel),  FeAsS;  or  as  a  by-product  in  the  preparation  of 
zaffre  from  cobaltite  (CoAsS),  or  smaltite  (CoAs2),  and  in  roasting 
certain  arsenical  tin  ores  before  smelting. 

The  roasting  is  done  in  reverberatory  furnaces,  and  the  vapors  of 
white  arsenic  sublime  off,  and  are  condensed  as  a  powder  in  long 
horizontal  canals,  or  in  chambers.  The  crude  product  is  purified  in 
a  small  reverberatory  furnace,  fired  with  coke,  or  in  cast-iron  pots,  a 
number  of  which  are  set  in  a  furnace,  all  being  connected  with  a  single 
condensing  chamber  or  canal.  Directly  over  the  pot  an  iron  drum  or 
cylinder  is  often  placed,  from  the  top  of  which  a  short  pipe  leads  to 
the  condensing  chamber. 

After  resubliming,  the  oxide  is  a  white  granular  powder,  which 
is  usually  ground  before  packing  for  market;  or,  by  a  second  subli- 
mation under  slight  pressure  in  an  atmosphere  of  arsenious  acid,  it 
is  obtained  in  an  amorphous  or  vitreous  state.  For  this  the  pot  is 
heated  red-hot,  and  the  "  arsenic  meal  "  introduced  through  an  open- 
ing in  the  cap  of  the  drum,  which  is  then  closed.  The  arsenic  vapor 
rises  into  the  drum,  and  condenses  on  its  walls  as  a  transparent  layer 
of  "  arsenic  glass." 

White  arsenic,  or,  as  it  is  commonly  called,  arsenic,  comes  in  com- 
merce as  a  powder,  and  as  a  "  glass."  On  standing,  the  latter  changes 
to  a  crystalline  state,  and  becomes  white,  opaque,  and  porcelain-like 
in  structure.  It  has  no  odor,  and  a  very  slight  metallic  taste,  is  diffi- 
cultly soluble  in  water,  and  vaporizes  without  melting  when  heated  in 
the  open  air.  It  is  used  in  glass-making ;  when  dissolved  in  glycerine, 
as  a  mordant  in  calico  printing;  in  making  various  pigments;  for 
preparing  fly  and  rat  poisons ;  as  a  preservative  for  green  hides ;  for 
the  manufacture  of  arsenic  salts  ;  for  insecticides  ;  in  medicine ;  and 
formerly,  to  a  great  extent,  in  the  preparation  of  aniline  from  nitro- 
benzene. 

Arsenic  acid,  H3AsO4,  is  prepared  by  heating  4  parts  arsenic  tri- 
oxide with  3  parts  concentrated  nitric  acid  (1.35  sp.  gr.),  and  evapo- 
rating the  solution  to  a  thick  syrup,  in  which  form  it  is  usually  sent 
to  market.  By  evaporating  it  to  dryness,  and  igniting  at  a  red  heat, 
arsenic  pentoxide,  A^Os,  a  hygroscopic  body,  is  formed. 


270  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

Arsenic  acid  attacks  the  skin,  producing  blisters,  but  is  less  poison- 
ous than  arsenious  acid.  It  is  chiefly  used  in  calico  printing,  but  was 
formerly  much  employed  as  an  oxidizing  agent  in  making  certain  coal- 
tar  dyes  (rosanilines). 

Sodium  arsenate,  Na2HAsO4,  is  made  by  heating  white  arsenic 
with  sodium  nitrate,  or  by  dissolving  white  arsenic  in  sodium  car- 
bonate solution,  adding  some  sodium  nitrate,  evaporating  to  dryness, 
and  calcining  the  mass.  By  dissolving  in  water,  and  crystallizing,  the 
salt  Na2HAsO4  •  12  H^O  is  obtained.  This  usually  contains  some 
NaH2AsO4  •  H2O  (binarsenate). 

It  is  used  as  a  substitute  for  the  "  dung-bath  "  in  dyeing  alizarines, 
and  in  calico  printing,  to  prevent  discoloration  of  the  white  parts  of 
the  pattern  by  rendering  the  excess  of  mordant  insoluble,  so  that  it 
does  not  "  bleed,"  i.e.  diffuse  into  the  white  portions  of  the  cloth. 

Sodium  arsenite,  NaAsO2  (meta-arsenite),  is  prepared  by  neutral- 
izing arsenious  acid  with  sodium  carbonate,  or  hydroxide  solution, 
and  boiling  for  some  time.  The  salt  has  been  used  instead  of  the 
"  dung-bath  "  in  dyeing. 

Orpiment  and  Realgar  have  been  described  on  pp.  240  and  245. 

Lead  arsenate,*  PbHAsO4,  or  Pb3(AsO4)2,  made  by  precipitation 
of  a  lead  acetate  or  nitrate  solution  with  sodium  arsenate,  is  a  white 
amorphous  powder  much  used  as  an  insecticide  spray  in  agriculture. 
It  is  less  injurious  to  foliage  and  adheres  better  than  Paris  green. 
It  should  not  contain  lead  arsenite,  which  is  more  soluble  and  hence 
affects  vegetation  seriously. 

*  Bui.  No.  121,  U.  S.  Bureau  Chemistry,  Dept.  Agriculture,  1910. 


WATER-GLASS 

The  substances  sold  under  this  name  are  silicates  of  sodium,  or 
potassium,  or  of  both.  They  are  soluble  in  water,  and  are  generally 
sold  as  thick,  syrupy  liquids. 

Commercial  water-glass  is  not  of  definite  composition,  but  is  ap- 
proximately Na2Si4Og.  It  is  prepared  by  fusing  powdered  quartz, 
or  infusorial  earth,  with  caustic  soda  or  with  sodium  carbonate.  A 
small  quantity  of  charcoal  is  also  added,  to  assist  in  the  complete 
reduction  of  the  carbonate.  Sodium  sulphate  may  be  used  instead  of 
the  carbonate.  The  fusion  is  done  in  a  reverberatory  furnace,  and 
requires  8  or  10  hours.  Sometimes  ordinary  glass-pots  and  furnaces 
(p.  199)  are  used.  The  product  is  a  translucent  or  transparent  glass, 
slightly  green,  from  traces  of  iron.  It  is  powdered,  and  boiled  in 
water,  best  in  a  digester  under  pressure,  until  the  soluble  matter  is 
dissolved.  A  small  quantity  of  copper  or  lead  oxide  is  added,  to 
decompose  any  sodium  sulphide  formed  during  the  reduction.  After 
10  or  12  hours  the  solution  is  drawn  from  the  boiler,  filtered  on  cloth, 
and  allowed  to  settle.  It  is  then  concentrated  to  140°  Tw.  (1.7  sp. 
gr.).  The  material  used  must  be  pure,  and  especially  be  free  from 
lime,  alumina,  etc. 

Water-glass  is  also  made  by  boiling  silica  in  a  digester  with  a  solu- 
tion of  caustic  soda  for  a  long  time  at  60  pounds  pressure.  This 
yields  a  solution  of  the  silicate  directly,  which  needs  only  a  little  con- 
centrating. Sometimes  gelatinous  precipitated  silica  is  dissolved  in 
caustic  soda,  and  the  solution  is  evaporated.  By  using  a  mixture  of 
equivalent  weights  of  sodium  and  potassium  carbonates,  a  more  soluble 
glass  is  produced,  which  is  sometimes  called  "  double  soluble  glass." 

Potassium  silicate,  which  forms  a  more  soluble  glass  than  sodium 
silicate  does,  is  made  in  the  same  way. 

Water-glass  is  readily  decomposed  by  acids,  even  carbon  dioxide 
setting  free  silica,  and  forming  a  salt  of  the  alkali.  It  is  used  exten- 
sively as  an  addition  to  yellow  or  laundry  soaps ;  as  a  fixative  for 
pigments  in  calico  printing ;  as  a  vehicle  for  pigments  in  fresco  paint- 
ing ;  for  rendering  cloth  and  paper  draperies  non-inflammable ;  as  a 
size  for  paper  and  fabrics ;  for  preserving  eggs ;  as  a  preservative  for 
timber  and  porous  stone  •  in  the  manufacture  of  artificial  stone ;  and 
in  cement  mixtures  for  glass,  pottery,  wood,  and  leather. 


271 


PEROXIDES 

Barium  peroxide  *  BaO2,  is  made  by  calcining  barium  nitrate,  and 
heating  the  oxide  thus  obtained  in  an  atmosphere  of  dry,  pure  air. 
The  nitrate  is  packed  in  crucibles,  and  heated  in  a  furnace  at  880°  C. 
for  several  hours.  The  mass  fuses,  and  for  the  first  3  or  4  hours 
continues  to  evolve  nitrous  gases,  but  finally  becomes  solid,  though  of 
a  spongy,  porous  character.  This  is  barium  monoxide,  and  must 
be  carefully  protected  from  moisture  and  carbon  dioxide.  It  is 
broken  up  into  small  lumps,  and  put  into  flat  iron  trays,  which  are 
set  in  wide,  cast-iron  pipes,  thrpugh  which  a  current  of  air  can  be 
passed.  The  air  is  dried  thoroughly,  and  freed  from  carbon  dioxide 
before  it  enters  the  pipes,  by  passing  it  through  a  drying  tower,  or 
drum,  filled  with  caustic  soda  or  quicklime.  The  pipes  are  heated  to 
a  low  red  heat  (400°  C.),  and  the  air  passes  through  them.  The 
barium  oxide  takes  up  an  atom  of  oxygen,  forming  the  peroxide, 
while  nitrogen  escapes  from  the  pipe.  The  product  is  cooled  away 
from  contact  with  air. 

By  adding  an  excess  of  barium  hydroxide  solution  to  a  solution 
of  hydrogen  peroxide,  a  precipitate  of  hydrated  barium  peroxide, 
BaO2  •  8  H2O  is  obtained,  which  is  stable.  By  drying  this  at  130°  C., 
all  the  water  is  expelled,  and  the  pure  peroxide  remains. 

Barium  peroxide  is  a  gray  or  white  powder,  insoluble  in  water, 
but  combining  with  it  to  form  a  hydrated  compound.  It  is  easily 
decomposed  by  dilute  acids,  and  even  takes  up  carbon  dioxide  from 
the  air.  Heated  to  a  bright  red  heat  (1000°  C.),  it  decomposes  into 
monoxide  and  free  oxygen.  Its  chief  uses  are  for  making  hydrogen 
peroxide,  and  in  the  preparation  of  oxygen  gas. 

Hydrogen  peroxide  f  H2O2,  is  made  by  decomposing  barium  perox- 
ide with  dilute  mineral  acids.  The  finely  powdered  barium  peroxide 
is  actively  stirred  into  diluted  hydrochloric  acid  in  which  blocks  of  ice 
are  floating.  The  temperature  must  not  rise  above  15°  C.  When  all 
the  peroxide  is  dissolved,  dilute  sulphuric  acid  in  slight  excess  is  added 
to  precipitate  the  barium.  Then  to  remove  iron  and  alumina,  some 
sodium  phosphate  is  added,  with  more  barium  peroxide  to  make  the 
solution  neutral;  finally  add  ammonia  to  decided  alkaline  reaction. 

*  J.  Soc.  Chem.  Ind.,  1890,  246.     L.  T.  Thome.     Chemiker-Zeitung,  1894,  68. 
t  Zeitschr.  f.  angew.  Chem.,  1890,  3.     G.  Lunge,     J.  Am.  Chem.  Soc.,  12,  64. 
A.  Bourgougnon.     J.  Soc.  Chem.  Ind.,  1902,  229. 

272 


PEROXIDES  273 

The  turbid  liquor  is  rapidly  put  through  a  filter-press,  and  the  clear 
filtrate  immediately  made  slightly  acid  with  sulphuric  acid,  as  the  al- 
kaline solution  will  not  keep.  Any  barium  remaining  in  solution  is 
precipitated  with  pure  sodium  sulphate  solution,  and  the  liquor  settled. 
Phosphoric  acid  may  be  used  instead  of  hydrochloric  and  gives  a 
stable  product ;  but  it  is  more  expensive.  The  commercial  strength 
is  known  as  a  12-volume  solution,  i.e.  3j  per  cent  H2O2. 

By  using  hydrofluoric  acid,  the  precipitate  of  barium  fluoride 
may  be  readily  employed  to  generate  more  of  the  acid ;  if  nitric  acid 
is  used,  a  considerable  part  of  the  barium  is  recovered  as  barium 
nitrate,  with  which  more  barium  peroxide  can  be  made. 

Hydrogen  peroxide  is  a  powerful  oxidizing  agent  towards  sub- 
stances capable  of  oxidation,  but  with  bodies  which  give  off  oxygen 
readily  it  acts  as  a  reducing  agent,  giving  up  one  atom  of  oxygen  to 
unite  with  the  oxygen  from  the  body  in  question,  forming  a  molecule 
of  the  free  gas.  It  is  used  extensively  as  a  bleaching  agent,  especially 
for  animal  fibres  and  tissues,  such  as  silk,  wool,  hair,  feathers,  bone, 
and  ivory.  It  has  long  been  used  as  a  hair  bleach  for  toilet  use.  As 
a  disinfectant  and  antiseptic,  it  finds  use  in  surgery;  for  restoring 
the  colors  of  oil  paintings  which  have  darkened  with  age,  it  is  very 
effective,  if  the  paint  contains  lead;  the  lead  sulphide  is  oxidized  to 
the  sulphate  by  the  peroxide,  the  black  color  of  the  former  being 
destroyed.  Hydrogen  peroxide  has  also  been  proposed  as  a  substitute 
for  sodium  bisulphite  and  thiosulphate,  as  the  reducing  material  for 
chrome  tannage  processes ;  also  as  an  antichlor,  for  use  after  chlorine 
bleaching;  and  as  a  general  antiseptic,  for  use  in  the  fermentation 
industries,  and  as  a  preservative  for  milk,  beer,  wine,  and  other  fer- 
mentable liquids. 

Sodium  peroxide,*  Na2O2,  has  recently  appeared  in  commerce  as  a 
bleaching  material.  The  technical  production  depends  upon  the  oxi- 
dation of  fused  metallic  sodium,  by  exposing  it  to  a  current  of  pure 
dry  air  or  oxygen.  The  sodium  is  contained  in  aluminum  trays, 
which  are  put  on  cars,  and  pushed  slowly  through  a  wide  iron  pipe, 
externally  heated  to  300°  C.,  while  air,  purified  as  described  on 
p.  272,  passes  through  the  pipe  in  the  opposite  direction.  The  temper- 
ature must  not  rise  above  300°  C.,  and  the  oxidation  must  be  slow. 

Sodium  peroxide  is  a  yellowish  white,  very  hygroscopic  powder, 
which  is  chiefly  used  as  a  powerful  bleaching  agent.  It  gives  off  20 

*  J.  Soc.  Chem.  Ind.,  1892,  1004  (Patent  to  H.  Y.  Castner)  ;  1893,  603.     Chem- 
ical Trade  Journal,  11,  208. 
T 


274  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

per  cent  of  its  weight  as  active  oxygen.*  It  dissolves  in  dilute  acids 
without  evolving  oxygen,  if  the  vessel  be  kept  cool,  yielding  a  strong 
solution  of  hydrogen  peroxide.  It  dissolves  in  water  with  the  loss 
of  some  oxygen,  and  a  great  evolution  of  heat,  which  may  be  suffi- 
cient to  set  fire  to  inflammable  bodies.  It  is  too  strongly  alkaline 
for  silk  or  wool  bleaching,  and  should  be  converted  into  magnesium 
peroxide  for  this  purpose.  This  is  easily  done  by  adding  magnesium 
sulphate  solution :  — 

Na2O2  +  MgSO4  =  Na2SO4  +  MgO2. 

The  solution  of  sodium  peroxide  attacks  cellulose,  and  produces 
an  effect  similar  to  that  obtained  by  "  mercerizing  "  with  caustic  soda. 

*  Barium  peroxide  liberates  8  per  cent  of  its  weight  of  active  oxygen,  while  a 
12-volume  solution  of  hydrogen  peroxide  liberates  only  1J  per  cent  of  its  weight  of 
active  oxygen. 


OXYGEN 

Numerous  processes  have  been  devised  for  the  technical  produc- 
tion of  oxygen,  but  most  of  them  are  so  expensive,  or  require  such 
complicated  plants,  that  only  two  or  three  are  in  actual  operation  on 
a  large  scale  at  the  present  time. 

The  decomposition  of  potassium  chlorate  by  heating,  with  the 
addition  of  manganese  dioxide,  has  been  much  employed,  and  is  still 
the  favorite  laboratory  method  of  obtaining  a  pure  gas.  The  addi- 
tion of  pyrolusite  lowers  the  temperature  of  the  decomposition,  and 
reduces  the  liability  of  explosion.  It  is  highly  important  that  the 
potassium  chlorate  and  pyrolusite  be  free  from  carbonaceous  matter. 

Boussingault's  process,  as  modified  by  Brin  brothers,  and  worked 
on  a  large  scale,  is  often  called  Erin's  process.*  Boussingault  dis- 
covered that  barium  peroxide  (BaO2),  when  heated  to  a  high  tempera- 
ture, decomposes  into  the  monoxide  and  oxygen,  the  latter  passing 
off.  Then  by  heating  the  barium  oxide  to  a  low  red  heat  in  a  current 
of  air,  the  peroxide  can  be  regenerated.  But  his  attempts  to  utilize 
the  process  were  unsuccessful,  because  the  monoxide  soon  became 
inert,  and  would  not  absorb  oxygen  from  the  air.  This  was  due  to 
the  fact  that  the  moisture  and  carbon  dioxide  in  the  air  converted 
the  barium  oxide  to  hydroxide  and  carbonate,  which  are  very  stable 
bodies,  even  at  high  temperatures,  consequently  the  regeneration  of 
peroxide  rapidly  decreased. 

As  modified  by  Brin  brothers,  the  temperature  of  the  retort  re- 
mains constant,  while  all  moisture  and  impurities  are  removed  from 
the  air.  Barium  oxide  is  made  from  barium  nitrate,  as  described  on 
p.  246,  and  put  into  vertical  retorts,  or  long  narrow  pipes,  suspended 
in  a  furnace  heated  by  producer  gas.  When  the  temperature  reaches 
700°  C.,  purified  air  is  forced  into  the  retorts  under  a  pressure  of  15 
pounds  per  square  inch,  and  the  monoxide  takes  up  an  atom  of  oxygen, 
and  forms  the  peroxide.  The  air  supply  is  then  cut  off,  and  the 
pump  reversed,  so  as  to  form  a  vacuum  in  the  retort,  reducing  the 
pressure  to  about  26  to  28  inches  of  mercury.  Under  these  condi- 
tions, the  barium  peroxide  gives  off  an  atom  of  oxygen,  and  is  reduced 
to  the  monoxide.  The  gas  is  pumped  into  the  gasometer,  and  when 
it  ceases  to  be  evolved  the  pump  is  reversed  again,  and  air  forced  into 
the  retort,  to  oxidize  the  monoxide  to  peroxide  again. 

*  J.  Soc.  Chem.  Ind.,  1890,  246.     L.  T.  Thome.     1889,  82  and  517. 

275 


276  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

The  air  is  passed  through  purifiers,  one  filled  with  quicklime,  and 
the  other  with  caustic  soda ;  these  remove  the  water  and  carbon  di- 
oxide. By  the  alternate  use  of  pressure  and  vacuum,  the  temperature 
may  be  kept  constant  at  700°  C.  The  oxygen  obtained  is  about  96 
per  cent  pure.  The  baryta  is  removed  once  in  six  or  eight  months, 
and  broken  up  to  prevent  caking,  after  which  it  is  returned  to  the 
retort.  The  yield  of  oxygen  gas  at  each  operation  is  said  to  be  about 
10  litres  per  kilo  of  barium  oxide  employed.  The  cost  of  the  gas  in 
England  is  from  3s.  to  7s.  per  1000  cubic  feet. 

Deville's  process.  —  By  allowing  sulphuric  acid  to  drop  in  fine 
streams  on  red-hot  surfaces,  it  breaks  up  according  to  the  reaction :  — 

2  H2SO4  =  2  S02  +  2  H20  +  O2. 

The  gases  evolved  are  passed  through  cooling  coils  to  condense  the  water, 
and  then  through  scrubbers  containing  water,  to  remove  the  sulphur 
dioxide.  The  retort  is  usually  filled  with  broken  brick,  pumice,  or  other 
porous,  acid-resisting  material.  The  process  has  no  significance  as  a 
method  of  preparing  oxygen  alone,  but  has  been  used  for  making  sulphuric 
anhydride,  SO3,  the  water  being  first  condensed,  and  the  sulphur  dioxide 
and  oxygen  uniting  to  form  the  trioxide.  About  114  litres  of  oxygen  are 
obtained  from  1  kilo  of  sulphuric  acid. 

Tessie  Du  Motay  process.*  —  This  depends  on  the  following  reac- 
tions :  — 

1)  2  Na2MnO4  +  2  H2O  =  Mn2O3  +  4  NaOH  +  3  O. 

2)  Mn203  +  4  NaOH  +  3  O(air)  =  2  Na2MnO4  +  2  H20. 

First,  sodium  manganate  is  prepared  by  mixing  a  manganese  oxide 
with  caustic  soda,  and  heating  with  free  access  of  air.  The  following 
reaction  takes  place :  — 

2  Mn02  +  4  NaOH  +  O2(air)  =  2  Na2Mn04  +  2  H2O. 

The  sodium  manganate  is  crushed,  mixed  to  a  paste  with  caustic 
soda  solution,  containing  from  5  to  10  per  cent  NaOH ;  this  is  dried 
slowly  and  completely  in  shallow  pans,  and  ignited  in  a  crucible  at  a  white 
heat,  to  render  it  spongy.  But  it  must  not  fuse.  .This  yields  a  porous 
manganate,  containing  an  excess  of  caustic  soda,  which  is  filled  into  long 
clay  or  cast-iron  retorts  of  peculiar  construction,  f  set  at  an  incline  in 
the  furnace,  and  heated  to  a  regular  temperature  of  400°-450°  C.  Super- 
heated steam  is  then  admitted  to  the  retort,  where  it  deoxidizes  the  man- 
ganate, regenerating  the  manganic  oxide  and  caustic  soda,  while  oxygen 
is  liberated,  and  is  cooled  and  collected  in  a  gasometer.  Then  the  process 
is  reversed,  and  purified  air,  which  has  passed  through  a  heating  pipe, 
set  in  the  furnace,  is  admitted  to  the  retort;  it  oxidizes  the  material, 

*  J.  Soc.  Chem.  Ind.,  1892,  312.     F.  Fanta. 
t  For  details,  see  J.  Soc.  Chem.  Ind.,  1892,  315. 


OXYGEN 


277 


regenerating  the  sodium  manganate,  while  pure  nitrogen  escapes.  The 
cycle  of  operations  is  repeated  indefinitely.  In  order  that  the  supply  of 
oxygen  may  be  continuous,  the  plant  is  usually  built  in  duplicate,  so 
that  the  contents  of  one  set  of  retorts  is  being  oxidized  with  air,  while 
that  of  the  other  is  being  deoxidized  with  steam. 

The  Linde  refrigeration  process*  employs  distillation  and  de- 
phlegmation  of  liquid  air,  which  is  made  by  the  refrigerating  effect 
produced  when  expanding  compressed  air  from  a  higher  to  a  lower 
pressure.  At  0°  C.,  each  decrease  of  one  atmosphere  pressure  causes 
a  drop  of  0.276°  C.,  in  the  temperature.  The  specific  heat  of  a  gas  in- 
creases with  increasing  pressure,  and  the  cooling  effect  is  greater  the 
lower  the  temperature  at  which  expansion  takes  place.  With  suitable 
apparatus  for  heat  interchange,  the  action  of  an  indefinite  number  of 
expansions  is  accumulated  and  intensified,  since  the  cold  gas  from 
each  expansion  serves  to  precool  the  compressed  air  before  the  next 
expansion.  Air  at  200  at- 
mospheres pressure  enters 
the  small  copper  tube  (Fig. 
91)  f  and  flows  down 

through    the    triple    Coil  of      Interchanger; 

the  heat  interchanger  and 
finally  through  a  copper 
coil  submerged  in  the 
liquid  air  in  the  bottom  hQ'  91' 

of  the  rectifier.  This  lowers  the  temperature  so  much  that  the 
compressed  air  is  liquefied  before  reaching  the  valve  (A),  by  which 
the  liquid  is  admitted  to  the  top  of  the  rectifying  column  which 
serves  as  a  dephlegmator.  Nitrogen,  having  a  boiling  point  of 
—  195.5°  C.,  tends  to  evaporate  much  faster  than  the  oxygen  boiling 
at  — •  182.5°  C. ;  thus  separation  is  effected  in  the  column,  oxygen 
descending  as  liquid,  and  nitrogen  ascending  as  gas.  The  cold  out- 
going gases  pass  through  the  heat  interchanger  coils  surrounding  the 
tube  containing  the  compressed  air,  from  which  they  absorb  heat  as 
they  escape  into  the  atmosphere.  By  allowing  much  of  the  liquid 
oxygen  to  vaporize  also,  a  residual  product  of  95  to  98  per  cent  pure 
is  obtained. 

The  production  of  oxygen  by  the  electrolysis  of  water  (with  some 
sodium  hydroxide  in  solution)  is  practised  commercially  in  this  country 
and  abroad.  About  3  cubic  feet  of  oxygen  and  6  cubic  feet  of  hydrogen 


Rectifier 


*  J.  Soc.  Chem.  Ind.,  1895,  984 ;   1903,  695.     U.  S.  Consular  Rep.,  54,  64. 
t  Publications  of  the  Linde  Air  Products  Company,  Buffalo,  N.Y. 


278  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

are  obtained  per  kilowatt-hour ;  each  cell  takes  350  amperes  at  2  volts. 
The  generator  consists  of  an  iron  tank,  about  3  feet  diameter  and  4 
feet  deep,  whose  wall  serves  as  the  cathode.  Suspended  from  the 
inside  of  the  cover  is  a  perforated  steel  cylinder,  serving  as  anode ;  an 
asbestos-cloth  diaphragm  surrounds  the  anode,  separating  it  from  the 
cell  wall  (cathode),  and  prevents  mingling  of  the  oxygen  and  hydro- 
gen, which  pass  off  by  separate  pipes  from  their  respective  compart- 
ments. Both  gases  are  obtained  very  pure. 

Oxygen  is  used  for  the  oxy-hydrogen  and  oxy-acetylene  flame,  in 
melting  platinum  and  other  refractory  metals ;  for  autogenous  weld- 
ing and  metal  cutting ;  in  the  calcium  light ;  in-  purifying  illuminat- 
ing gas;  to  destroy  fusel  oil  in  high  wines;  and  in  treatment  of 
asphyxia  and  heart  weakness.  Its  use  has  been  proposed  to  hasten 
melting  and  refining  of  glass ;  for  enriching  air  in  the  blast-furnace 
and  steel  converter ;  for  oxidizing  drying  oils,  and  to  assist  the  action 
of  bleaching  powder  in  textile  work. 

REFERENCES 

Chemical  Trade  Journal,  1887,  145. 

Journal  of  the  Society  of  Chemical  Industry :  — 

1885,568.    1889,82,517.    1890,246.   1892,312.     1895,984.     1903,695. 

1911,  333.     Ozone. 

Chemische  Industrie,  1890,  104,  120;    1891,  71.     G.  Kassner. 
L'Ozone  et  ses  Applications  Industrielles.     H.  de  la  Caux.     Paris,  1910. 


SULPHATES 

The  sulphates  of  ammonium,  magnesium,  potassium,  and  sodium 
were  discussed  in  connection  with  the  industries  to  which  they  are 
related. 

Ferrous  sulphate,  green  vitriol,  or  copperas,  FeSO4  •  7  H2O,  is  a 
by-product  of  several  industries.  Pyrites  may  be  exposed  to  moist 
air  until  oxidation  takes  palce ;  by  lixiviation,  a  solution  of  ferrous 
and  ferric  sulphates,  and  sulphuric  acid,  is  obtained,  which  is  run  over 
scrap  iron.  The  reaction  reduces  all  ferric  salts,  and  the  clarified 
and  concentrated  liquor  yields  light  green  crystals  FeSO4  •  7  H2O. 

FeS2  +  H2O  +  7  O  =  FeSO4  +  H2SO4. 

The  basic  ferric  sulphate  from  the  manufacture  of  aluminum 
sulphate  from  shale  (p.  286)  yields  copperas  by  treatment  with  acid 
and  scrap  iron.  The  "  sludge  acid  "  of  petroleum  refining  is  some- 
times used  for  ferrous  sulphate,  by  diluting  and  dissolving  scrap 
iron  in  it.  The  acid  "  pickle  liquors,"  used  in  foundries  and  wire 
mills  for  cleaning  the  surfaces  of  castings  and  wire,  are  treated 
with  scrap  iron  to  neutralize  free  acid,  and  yield  more  copperas 
on  evaporation,  than  the  market  demands ;  the  disposal  of  the  ex- 
cess is  an  industrial  problem  to  prevent  contamination  of  surface 
waters. 

Wet  metallurgical  processes  for  producing  cement  copper  (p.  616) 
furnish  considerable  copperas.  Copper  sulphide  ores,  low  in  copper, 
are  weathered  in  heaps  for  several  months,  and  frequently  moistened 
with  water.  Oxidation  of  the  sulphides  forms  copper  and  iron  sul- 
phates, and  when  leached  the  liquors  run  into  tanks  containing  scrap 
iron ;  copper  precipitates  and  ferric  sulphate  is  reduced  to  the  ferrous 
state.  The  solution  is  clarified  and  evaporated  to  crystallize. 

All  processes  for  making  ferrous  sulphate  yield  dilute  solutions, 
which  are  best  evaporated  by  over-surface  heating  (p.  4),  to  prevent 
oxidation.  The  clarified  liquid  is  put  into  lead-lined  tanks,  in  which 
strings  or  wooden  rods  are  suspended ;  on  these  the  large  bluish  green 
crystals  of  ferrous  sulphate  form.  The  crystals  effloresce  quickly 
when  exposed  to  the  air,  and  become  coated  with  a  brownish  white 
powder  of  basic  ferric  sulphate,  formed  by  oxidation ;  ultimately 
the  entire  crystal  is  converted  to  this  basic  salt.  By  adding  alcohol 

279 


280  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

to  a  ferrous  sulphate  solution,  the  salt  is  precipitated  in  fine  crystals 
which  are  more  stable  in  the  air  than  are  the  ordinary  kind. 

Ferrous  sulphate  crystals  have  7  molecules  of  crystal  water ;  when 
heated  to  140°  C.,  6  molecules  of  water  are  expelled,  but  the  last  mole- 
cule is  not  removed  until  the  temperature  reaches  260°  C.,  when  basic 
salt  begins  to  form.  At  a  red  heat,  sulphuric  anhydride  is  given  off 
and  ferric  oxide  is  left. 

Copperas  solution  oxidizes  quickly  in  the  air,  and  a  yellow  pre- 
cipitate of  basic  ferric  sulphate  separates.  Commercial  green  vitriol 
often  contains  copper  sulphate,  and  sometimes  nickel  sulphate;  if 
large  quantities  of  these  impurities  are  present,  the  color  is  very  dark, 
and  the  salt  is  called  "  black  vitriol." 

Ferrous  sulphate  is  largely  used  as  a  mordant  in  dyeing;  in  the 
preparation  of  horticultural  sprays;  for  disinfecting  purposes;  for 
the  purification  of  water  supplies ;  in  the  manufacture  of  ink,  Prussian 
blue,  and  various  pigments ;  and  for  precipitating  gold  from  solution 
in  metallurgical  processes. 

Copper  sulphate,  blue  vitriol,  or  "bluestone,"  CuSO4  •  5  H2O,  is 
now  largely  obtained  as  a  by-product  in  the  "  parting  "  of  gold  and 
silver  with  sulphuric  acid.  The  gold  and  silver  alloy  is  boiled  with 
concentrated  sulphuric  acid  in  cast-iron  pans ;  the  silver  is  dissolved, 
the  solution  separated  from  the  residue  of  gold,  and  the  silver  sulphate 
decomposed  with  metallic  copper.  Metallic  silver  precipitates,  and 
copper  sulphate  remains  in  solution. 

Copper  sulphate  is  also  prepared  by  allowing  sulphuric  acid  to 
drip  on  scrap  copper  with  free  access  of  air,  the  copper  being  slowly 
oxidized  and  dissolved.  Or  metallic  copper,  contained  in  lead-lined 
tanks,  may  be  treated  with  hot  acid.  Scrap  copper  is  often  heated 
red-hot  in  a  furnace,  and  then  sulphur  is  thrown  in,  and  the  door 
tightly  closed.  Cuprous  sulphide  is  formed,  which  is  then  oxidized 
at  a  red  heat  by  admitting  air  into  the  furnace.  A  mixture  of  copper 
sulphate  and  oxide  is  thus  produced,  which  is  treated  with  hot  dilute 
sulphuric  acid,  and  the  solution  so  obtained  is  evaporated. 

1)  2  Cu  +  S  =  Cu2S. 

2)  Cu2S  +  5  O  =  CuS04  +  CuO. 

3)  (CuSO4  +  CuO)  +  H2SO4  =  2  CuSO4  +  H2O. 

Copper  sulphide  ores,  chalcopyrite,  and  chalcocite,  and  artificial 
copper  mattes  are  sometimes  converted  into  blue  vitriol;  but  the 
ferrous  sulphate  formed  crystallizes  with  the  copper  sulphate.  Such 


SULPHATES  281 

blue  vitriol  is  much  used  where  iron  is  not  injurious.  The  iron  may 
be  removed  by  roasting  the  salt  until  the  ferrous  sulphate  is  decom- 
posed into  oxide,  and  then  dissolving  in  water  and  recrystallizing. 
Or  the  solution  may  be  boiled  with  a  little  nitric  acid  or  lead  peroxide, 
until  the  iron  is  converted  to  the  ferric  state,  when,  by  adding  copper 
carbonate,  or  oxide,  or  barium  carbonate,  and  boiling  again,  the  iron 
precipitates. 

Some  copper  ores  contain  zinc,  and  yield  a  bluestone,  contami- 
nated with  zinc  sulphate.  The  acid  "  dipping  liquors  "  from  copper 
and  brass  works  are  also  used  for  blue  vitriol,  but  these  are  gener- 
ally contaminated  with  zinc.  The  hammer-scales  (copper  oxide),  pro- 
duced in  rolling  and  working  sheet  copper,  are  often  dissolved  in  dilute 
acid  to  form  blue  vitriol. 

Copper  sulphate  forms  deep  blue  crystals,  containing  5  molecules 
of  water.  In  dry  air  the  crystals  effloresce  and  fall  to  a  white  powder, 
but  all  the  water  does  not  escape  until  the  mass  is  heated  to  240°  C. 
The  anhydrous  salt  is  a  white  powder,  and  will  abstract  water  from 
alcohol  or  organic  liquids.  Bluestone  is  largely  used  as  a  mordant 
in  calico  printing,  and  in  dyeing ;  for  preparing  other  copper  salts  and 
pigments ;  in  the  preparation  of  germicides  and  insecticides  (Bordeaux 
mixture,  etc.),  for  batteries,  and  electrolytic  baths;  in  metallurgy, 
and  in  most  operations  where  a  soluble  copper  salt  is  desired. 

Zinc  sulphate  or  white  vitriol,  ZnSO4  •  7  H2O,  is  not  of  very  great 
importance.  It  is  made  by  roasting  zinc  blende  (sphalerite),  or  zinc- 
lead  ores,*  and  leaching  the  mass  with  water  or  dilute  sulphuric  acid. 
Or  scrap  zinc  is  dissolved  in  dilute  acid.  The  solution  may  be  purified 
from  copper  by  introducing  a  plate  of  metallic  zinc,  upon  which  the 
copper  deposits.  Iron  is  removed  by  heating  the  solution  in  the  air 
for  a  considerable  time,  while  stirring  well,  and  then  adding  a  small 
amount  of  zinc  carbonate  or  oxide,  to  precipitate  the  ferric  oxide. 

Zinc  sulphate  forms  colorless  crystals  containing  7  molecules  of 
water,  which  effloresce  in  the  air.  It  is  very  soluble  in  water.  When 
heated,  the  crystals  melt  in  their  water  of  crystallization,  and  at  100° 
C.,  6  molecules  of  water  are  expelled.  The  final  molecule  is  driven 
off  at  300°  C.,  while  at  a  red  heat  the  anhydrous  salt  decomposes, 
leaving  a  residue  of  zinc  oxide. 

Zinc  sulphate  is  used  somewhat  in  dyeing  and  printing ;  as  a 
disinfectant ;  for  preserving  and  clarifying  glue  solutions ;  in  medi- 
cine as  an  astringent,  and  in  lotions;  in  the  preparation  of  dryers 

*  Bruno  Kerl,  Mineral  Industry,  1895,  83. 


282  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

for  "  boiled  oils  " ;   and  to  some  extent  as  a  preservative  for  hides 
and  timber. 

Aluminum  sulphate,  A12(SO4)3,  18  H2O,  is  extensively  employed  in 
the  arts,  under  the  name  "  concentrated  alum."  It  is  usually  pre- 
pared from  pure  kaolin,  or  from  bauxite  [Al2O(OH)4,  or  A^Os  •  2  H2O], 
or  from  the  hydrated  alumina  obtained  in  the  cryolite  soda  process 
(p.  113)  or  Bayer's  process  (p.  283).  Aluminum  hydroxide,  prepared 
from  bauxite  or  cryolite,  is  almost  entirely  free  from  iron,  since  it  is 
precipitated  from  an  alkaline  solution  of  sodium  aluminate,  in  which 
the  iron  of  the  mineral  is  not  soluble.  When  this  hydroxide  is  dis- 
solved in  pure  sulphuric  acid,  a  very  pure  aluminum  sulphate  is 
formed. 

(a).  Aluminum  sulphate  from  clay :  —  China  clay,  free  from  cal- 
cium carbonate,  is  calcined  at  a  moderate  heat,  until  nearly  all  of  its 
water  is  expelled;  then  it  is  powdered  and  sifted  through  very  fine 
sieves,  and  mixed  with  a  little  less  than  the  theoretical  quantity  of 
sulphuric  acid  of  1.45  to  1.50  sp.  gr.,  and  heated  with  free  steam  to 
start  the  reaction,  which  soon  becomes  very  violent.  The  mass 
swells,  and  quantities  of  steam  escape,  but  when  the  reaction  ceases, 
the  swelling  subsides.  If  it  is  now  allowed  to  cool,  a  stonelike  sub- 
stance is  obtained,  which  is  employed  in  the  arts  as  "  alum  cake." 
It  contains  all  the  silica  and  iron  impurities  of  the  clay,  and  usually 
from  2  to  3  per  cent  of  free  acid.  But  if  the  thick  pasty  mass  is  diluted 
with  warm  water  while  still  hot,  and  decanted  or  filtered  from  the 
insoluble  impurity,  a  solution  of  the  sulphate  is  obtained,  which  on 
evaporation  yields  a  salt  containing  about  0.2  per  cent  iron,  and  a 
trace  of  free  acid.  It  is  often  customary  to  convert  this  solution  di- 
rectly into  alum  (p.  285),  by  adding  the  necessary  alkaline  sulphate. 

(b).  Aluminum  sulphate  from  bauxite  :  —  Bauxite  is  more  easily 
decomposed  by  acid  than  is  clay,  but  if  dissolved  directly,  the  product 
contains  a  large  amount  of  iron.  However,  considerable  bauxite  is 
decomposed  with  acid  to  form  a  hard  cake  which  is  known  in  trade 
as  "  alumino-ferric  cake,"  and  is  used  for  many  purposes  where  iron 
and  free  acid  do  no  harm,  and  a  cheap  source  of  soluble  alumina  is 
desired,  e.g.  in  precipitating  sewage  and  waste  liquors  from  dyeworks. 

But  a  pure  sulphate  is  obtained  by  the  following  processes :  The 
bauxite  is  roasted,  powdered  very  fine,  and  mixed  with  calcined  and 
finely  powdered  soda-ash,  in  the  proportion  of  1  molecule  of  Al2Os 
to  1.1  molecules  of  Na2O.  If  the  bauxite  contains  much  silica, 
more  soda  may  be  used,  but  the  amount  should  not  be  sufficient  to 


SULPHATES  283 

leave  free  carbonate  in  the  product  after  calcination,  otherwise  the 
mass  may  fuse,  and  the  solution  of  sodium  aluminate  obtained  by 
lixiviating  will  be  unstable.  The  mixture  is  calcined  at  a  white  heat, 
until  all  carbon  dioxide  and  water  are  expelled ;  this  requires  3  or  4 
hours.  The  product  is  a  porous,  pale  green  or  blue  mass,  which  is 
ground  and  lixiviated  with  hot  water,  in  a  wooden  tank,  while  stirring 
actively.  A  little  caustic  soda  is  added  to  the  water,  to  prevent  pre- 
cipitation of  alumina  (see  Bayer's  process,  below).  The  lixivia- 
tion  must  be  rapid,  not  occupying  more  than  10  minutes,  after  which 
the  solution  of  aluminate  is  decanted.  According  to  Jurisch,*  the 
liquor  should  be  at  least  35°  Be.  density,  and  contain  170  grams  A^Os, 
and  182  grams  Na2O,  per  litre.  Weaker  solutions  are  said  to  yield  a 
slimy  precipitate  of  alumina,  when  decomposed  in  the  next  stage  of 
the  process.  The  liquor  is  quickly  filtered  (in  a  filter  press),  heated 
to  90°  C.,  and  decomposed  by  passing  carbon  dioxide  into  it,  by  which 
hydrated  alumina  is  precipitated  in  a  granular  form,  which  is  readily 
washed  free  from  soda.  The  silica  remains  dissolved  in  the  mother- 
liquor.  The  carbon  dioxide  may  be  derived  from  limekiln  gases, 
or  from  the  calcination  of  sodium  bicarbonate. 

The  pure  aluminum  hydroxide  thus  made  is  added  slowly  to  hot, 
pure,  concentrated  sulphuric  acid,  until  the  frothing  ceases ;  the  solu- 
tion, cooled  in  flat  lead  pans,  forms  a  crystalline  mass.  If  an  excess 
of  alumina  is  used  in  neutralizing,  basic  salt  results.  Sulphate  made 
thus  is  nearly  free  from  iron  and  silica,  but  may  contain  small  quan- 
tities of  soda.  It  is  used  in  the  arts  under  the  name  of  "  concentrated 
alum."  From  analysis,  the  formula  appears  to  be  Al^SOJs  •  20  H2O, 
but  the  excess  of  water  may  be  hygroscopic  and  not  combined. 

The  process  of  J.  K.  Bayer  f  yields  very  pure  alumina.  A  caustic 
soda  liquor  of  1.48  sp.  gr.  (47°  Be.)  is  digested  for  six  hours  under  4 
atmospheres'  pressure,  at  170°  C.,  with  finely  powdered  bauxite, 
while  actively  stirred.  The  aluminum  hydroxide  of  the  bauxite  dis- 
solves to  form  sodium  aluminate  solution,  having  about  1  A12O3  to 
1.8  NazO.  The  solution  is  diluted  to  1.20  sp.  gr.  (24°  Be.),  filter- 
pressed  rapidly,  and  then  decomposed  in  tanks  by  agitating  for  about 
72  hours,  with  a  large  excess  of  aluminum  hydroxide.  The  hydroxide 
precipitates  in  crystalline  form,  until  the  proportions  are  about  1 
A12O3  to  6  Na2O ;  silica  and  impurities  remain  in  solution.  A  sufficient 
quantity  of  the  milky  liquid,  carrying  in  suspension  as  much  aluminum 

*  Fabrikation  von  Schwefelsaure  Thonerde,  52. 

t  Jurisch,  Ibid.,  17-18.  German  patents,  43,977  (1887)  and  65,604  (1892). 
J.  Soc.  of  Chem.  Ind.,  1888,  625. 


284  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

hydroxide  as  was  dissolved  from  the  bauxite,  is  withdrawn  and  filter- 
pressed.  The  caustic  soda  liquor  is  again  concentrated  to  1.48  sp. 
gr.  and  the  cycle  repeated.  The  silica  dissolved  in  the  aluminate 
solution  is  precipitated  during  the  digestion  as  an  insoluble  double 
silicate  of  sodium  and  aluminum  (Na2Al2Si3Oio  +  9  H2O),  and  remains 
with  the  residue,  together  with  the  iron.  The  hydrated  alumina  pre- 
cipitated is  washed  free  from  sodium  salts,  and  dissolved  in  acid  as 
described.  It  is  also  used  for  metallic  aluminium  (p.  638). 

Another  process  for  sulphate  consists  in  dissolving  bauxite  in 
dilute  acid,  at  a  temperature  of  90°  C.,  with  the  addition  of  a  little 
sodium  nitrate  to  oxidize  all  the  iron  to  the  ferric  state;  then  more 
bauxite,  together  with  a  little  potash  alum,  is  added.  After  stirring 
thoroughly,  the  whole  is  left  for  several  weeks.  The  iron  combines 
with  some  of  the  alumina  to  form  a  precipitate:  — 

2  A12(SO4)3  +  2  Fe(OH)3. 

(c).  Sulphate  from  cryolite :  —  The  hydrated  alumina  obtained  in 
the  cryolite  soda  process  (p.  113)  may  be  dissolved  to  make  aluminum 
sulphate  in  the  usual  way.  The  product  may  contain  some  soda. 

Another  method  of  utilizing  cryolite  depends  on  the  following  re- 
actions :  — 

1)  6  NaF,  2  A1F3  +  6  Ca(OH)2  =  6  CaF2  +  2  Al(NaO)3  +  6  H2O. 

2)  2  Al(NaO)3  +  6  NaF,  2  A1F3  :=  2  A12O3  +  12  NaF. 

3)  A12O3  +  3  H2SO4  =  A12(SO4)3  +  3  H2O. 

Powdered  cryolite  is  boiled  with  milk  of  lime,  and  the  solution 
of  sodium  aluminate  decanted.  By  boiling  the  aluminate  liquor  for 
a  long  time,  with  more  powdered  cryolite,  while  stirring  thoroughly, 
the  second  reaction  takes  place ;  the  residue  is  chiefly  hydrated  alu- 
minum oxide,  while  sodium  fluoride  goes  into  solution.  By  boiling 
the  latter  with  milk  of  lime,  caustic  soda  may  be  obtained  as  a  by- 
product. 

2  NaF  +  Ca(OH)2  =  CaF2  +  2  NaOH. 

By  evaporating  an  aluminum  sulphate  solution  until  very  con- 
centrated, and  then  cooling,  a  solid  cake  of  the  salt  having  a  crystal- 
line structure  is  obtained ;  its  composition  corresponds  to 

A12(SO4)3  •  20  H2O. 

It  is  difficult  to  obtain  single  crystals,  but  the  usual  formula  assigned 
to  them  is  A12(SO4)3  •  18  H2O.  The  commercial  product,  however, 


SULPHATES  285 

never  corresponds  exactly  to  this  formula.  As  now  prepared,  it  con- 
tains but  little  free  acid,  or  excess  of  alumina  (basic  salt),  and  only 
a  minute  trace  of  iron.  It  should  contain  14  to  14.5  per  cent  Al2Oa, 
and  dissolve  readily  in  water  to  form  a  clear  solution,  i.e.  no  basic 
salt  should  be  present.  About  0.5  per  cent  free  acid  and  0.01  to 
0.1  per  cent  Fe2O3  are  the  average  content  of  commercial  samples. 
Since  it  may  now  be  had  of  great  purity,  aluminum  sulphate  has 
largely  replaced  alum  in  the  arts.  It  is  extensively  used  as  a  mordant 
in  dyeing;  in  preparing  size  for  paper;  for  making  alum  and  alu- 
minum salts  (red  liquor,  etc.) ;  in  tawing  skins ;  for  precipitating 
sewage  or  coloring  matter  from  water;  and,  in  general,  for  all  pur- 
poses where  alum  was  formerly  used. 

ALUM 

An  alum  is  a  double  sulphate  of  a  univalent  alkali  metal  and  a 
hexad  metallic  radical  of  the  form  (R2)  ==»  crystallized  with  24  mole- 
cules of  water.  The  general  formula  is  therefore 

•  M2SO4,  R2(SO4)3  •  24  H2O, 

or,  as  it  is  more  frequently  written,  MR(SO4)2  •  12  H2O.  The  alkali 
metal  may  be  sodium,  potassium,  ammonium,  lithium,  caesium,  or 
rubidium.  The  hexad  radical  contains  aluminum,  chromium,  iron,  or 
manganese.  In  the  majority  of  alums  the  essential  part  is  aluminum 
sulphate,  but  since  this  does  not  crystallize  well  alone,  it  has,  until 
recently,  been  difficult  to  obtain  it  pure  enough  for  some  purposes. 
But  the  addition  of  an  alkali  sulphate  forms  alum,  which  crystallizes 
beautifully  and  is  very  pure,  while  the  alkali  sulphate  itself  has  no 
injurious  action  in  most  cases  where  aluminum  sulphate  is  used.  But 
since  "  concentrated  alum  "  (p.  283)  can  now  be  had  very  pure,  it  is 
generally  preferred,  because  of  its  greater  strength  and  solubility. 

All  alums  crystallize,  with  the  same  number  of  molecules  of  water, 
in  the  regular  system,  either  as  octahedrons,  or  as  cubes.  They  are 
all  isomorphous,  and  a  crystal  of  one  kind  of  alum  will  continue  to 
grow  by  accretion,  if  placed  in  a  solution  of  another  alum.  Alum 
crystallizes  from  solution  very  perfectly,  and  forms  exceedingly  pure 
crystals,  even  from  impure  solutions. 

Alum  occurs  in  nature  in  small  quantities,  produced  by  the  action 
of  volcanic  gases  on  rocks  consisting  of  potash-aluminum  silicates; 
also  in  combination  with  iron  and  aluminum  hydroxides  in  the  mineral 
alunite,  or  alum  stone,  K2SO4,  A12(S04)3,  4  A1(OH)3,  also  formed  by 


286  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

volcanic  action.     Other  sources  are  alum  slates  and  shales,   clay, 
bauxite,  and  cryolite. 

Alunite,  or  alum  stone,  is  insoluble  in  water.  It  is  calcined  in 
heaps,  or  in  small  shaft  kilns,  at  about  500°  C.,  and  the  mass  is  then 
exposed  to  the  weather  for  several  months,  being  moistened  from 
time  to  time.  The  calcination  converts  the  iron  and  aluminum  hy- 
droxide into  insoluble  oxides,  and  the  weathering  forms  alum  in 
the  mass,  which  is  dissolved  by  lixiviation,  and  recrystallized.  The 
alum  thus  obtained  is  basic,  and  crystallizes  in  cubes ;  owing  to  im- 
perfect settling  of  the  liquors  before  crystallization,  some  iron  oxide 
is  enclosed,  giving  the  crystals  a  red  color.  This  iron  is,  however, 
quite  insoluble,  and,  no  free  acid  being  present,  the  alum  yields  a 
pure,  neutral  solution,  and  is  especially  desired  for  some  purposes. 
It  is  made  at  Tolfa,  near  Rome,  and  so  is  called  Roman  alum.  An 
imitation  is  made  by  coloring  alum  crystals  derived  in  other  ways, 
with  brick  dust,  or  with  iron  oxide  (Venetian  red).  For  further  refer- 
ences on  alunite  see  p.  158. 

Alum  slates  or  shales  are  mixtures  of  iron  pyrites,  aluminum 
silicates,  and  bituminous  matter.  By  exposure  to  the  weather,  the 
pyrites  is  oxidized  to  ferrous  sulphate  and  sulphuric  acid,  and  these 
react  with  the  aluminum  silicate  to  form  aluminum  sulphate.  Basic 
ferric  sulphate  is  also  formed.  The  oxidation  can  be  greatly  hastened 
by  roasting  the  shale  before  weathering  it,  but  the  temperature  must 
not  be  high  enough  to  drive  off  the  sulphur.  After  weathering,  the 
mass  is  systematically  lixiviated,  and  a  solution  of  aluminum  sul- 
phate, having  a  specific  gravity  of  about  1.16,  containing  some  calcium 
and  iron  sulphates,  comes  from  the  leach  tanks.  This  is  clarified  by 
settling,  and  some  of  the  calcium  and  basic  ferric  sulphates  deposit. 
The  solution  is  evaporated  in  lead  or  iron  pans  by  surface  heating 
with  direct  flame,  until  ferrous  sulphate  crystallizes  on  cooling,  and 
then  the  mother-liquor  containing  the  aluminum  sulphate  is  further 
concentrated  to  1.40  sp.  gr.  During  this  evaporation,  more  calcium 
sulphate  and  a  basic  ferric  sulphate  separate.  Scrap  iron  is  generally 
placed  in  the  vessel  during  concentration,  to  convert  the  ferric  sul- 
phate into  the  basic  salt,  and  to  reduce  the  destructive  action  on  the 
pan.  The  hot  solution  is  decanted  from  the  sediment,  and  mixed 
with  potassium  or  ammonium  sulphate  in  exact  amount  to  form  the 
alum.  By  agitating  the  liquid  during  the  cooling,  very  fine  crystals 
of  alum,  called  "  alum  meal,"  separate. 

If  the  aluminum  sulphate  solution  contains  much  iron,  as  is  gen- 
erally the  case  when  working  on  a  large  scale,  it  is  often  the  practice 


SULPHATES  287 

to  add  potassium  chloride  to  form  the  alum.  By  decomposing  the 
iron  sulphates,  this  forms  potassium  sulphate  in  the  solution,  and,  at 
the  same  time,  converts  the  iron  into  the  very  soluble  ferric  and 
ferrous  chlorides,  which  remain  in  the  solution  when  the  alum  sepa- 
rates. But  with  a  pure  solution  of  aluminum  sulphate,  this  causes 
loss  by  converting  part  of  the  aluminum  into  the  very  soluble  alu- 
minum chloride :  — 

4  A12(SO4)3  +  6  KC1  =  3  5K2SO4,  A12(SO4)3J  +  2  A1C13. 

The  alum  meal  is  washed  with  cold  water  in  a  centrifugal  machine 
and  recrystallized.  It  is  sold  both  in  the  crystallized  and  in  the 
powdered  form. 

The  manufacture  of  alum  from  clay,  bauxite,  or  cryolite  involves 
the  preparation  of  a  pure  solution  of  aluminum  sulphate  by  methods 
already  given,  and  the  addition  of  the  exact  quantity  of  alkali  sulphate 
to  form  the  alum. 

Blast  furnace  slag  has  been  proposed  as  a  source  of  alum.  It  is 
decomposed  with  hydrochloric  acid,  and  the  aluminum  chloride  solu- 
tion is  decomposed  with  calcium  carbonate ;  the  aluminum  hydroxide 
so  obtained  is  dissolved  in  sulphuric  acid.  The  process  is  not  suc- 
cessful, however. 

"  Neutral  alum  "  is  made  by  adding  sodium  or  potassium  carbon- 
ate, or  caustic  soda  to  an  alum  solution,  until  a  slight  precipitate  re- 
mains, even  after  vigorous  agitation.  After  filtering,  cubical  crystals 
of  the  neutral  alum  can  be  obtained,  but,  as  a  rule,  the  neutral  solu- 
tion is  made  by  the  user,  and  is  not  crystallized.  Neutral  alum  is 
much  used  in  mordanting,  because  of  the  great  readiness  with  which 
it  deposits  alumina  on  the  fibre. 

The  most  important  alums  of  commerce  are  potassium  alum, 
K2SO4  •  A12(SO4)3  •  24  H2O,  and  ammonium  alum 

(NH4)2S04  •  A12(SO4)3  •  24  H2O. 

The  latter  is  less  soluble  than  the  potash  salt,  but  in  all  other  respects 
they  are  quite  similar.  Both  are  stable  in  the  air. 

Sodium  alum,  Na2SO4  •  A12(SO4)3  •  24  H2O,  is  very  soluble  in  water 
and  difficult  to  purify.  Moreover,  the  crystals  effloresce  on  exposure 
to  the  air ;  in  this  condition,  they  are  sometimes  sold  as  "  porous 
alum." 

When  heated,  alum  loses  water  and  some  sulphuric  acid,  and  falls 
to  a  white  powder,  "  burnt  alum,"  which  is  difficultly  soluble  in  water. 
This  is  used  occasionally  as  a  caustic  in  medicine. 


288  OUTLINES    OF   INDUSTRIAL   CHEMISTRY 

The  chief  uses  of  common  alum  are  as  a  mordant  in  dyeing;  in 
preparing  size  for  paper-making;  in  tawing  skins;  in  making  pig- 
ment lakes;  for  clarifying  turbid  liquids,  and  precipitating  sewage; 
and  for  hardening  plaster  of  Paris  casts,  and  other  articles. 

Besides  the  common  alums  of  trade,  containing  aluminum  sul- 
phate as  a  basis,  two  others,  iron  alum  and  chrome  alum,  are  also 
employed  in  the  arts  to  some  extent. 

Iron  alum,  which  may  be  either  (NH4)2SO4,  Fe2(SO4)3  •  24  H2O,  or 
K2SO4,  Fe2  (804)3  *  24  H2O,  is  made  by  oxidizing  a  copperas  solution 
to  form  ferric  sulphate,  adding  the  proper  quantity  of  alkali  sul- 
phate, and  cooling  below  10°  C.  It  forms  pale  violet  crystals,  which 
are  rather  unstable,  efflorescing  and  oxidizing  in  the  air,  forming  basic 
ferric  salt.  Iron  alum  is  chiefly  used  as  a  mordant. 

Chrome  alum,  K2SO4,  Cr2(SO4)3  •  24  H2O,  is  largely  produced  as  a 
by-product  in  the  manufacture  of  alizarine.  A  mixture  of  potassium 
bichromate  and  sulphuric  acid  is  employed  to  oxidize  anthracene 
(CuHio)  to  anthraquinone  (Ci4H8O2),  from  which  the  alizarine  is  pro- 
duced. The  effect  of  the  reducing  action  of  the  organic  body  on  the 
bichromate  mixture  is  to  form  potassium  and  chromium  sulphates  in 
the  solution  in  proper  proportion  to  unite  in  chrome  alum :  — 

CuHio  +  K2Cr2O7  +  4  H2SO4  =  Ci4H8O2  +  K2SO4,  Cr2(SO4)3  +  5  H2O. 

Chrome  alum  forms  deep  violet  crystals,  which  effloresce  on  ex- 
posure to  the  air.  It  is  used  as  a  mordant;  and  in  tawing  skins, 
especially  in  certain  chrome  tannage  processes. 

REFERENCES 

Die  Fabrikation  des  Alauns,  des  Bleiweisses  und  des  Bleizuckers.     Dr.  F. 

Junemann,  Leipzig,  1882.     (Hartleben.) 

Die  Fabrikation  von  schwefelsaure  Thonerde.     K.  W.  Jurisch,  Berlin,  1894. 
Journal  of  the  Society  of  Chemical  Industry :  — 

1882,  124.     Newlands.     1883,  482.     Kyiiaston.     1886,   16.     Beveridge. 

1888,  625.     (Bayer's  Patent  for  Alumina  Hydrate.)     1892,  4  and  321. 
Chemical  News,  42,  191  and  202. 

Mineral  Resources  of  the  United  States.     1893,  159 ;  1903,  265  ;  1904,  285. 
Bulletin  No.  315,  U.  S.  Geological  Survey,  1906,  215. 


CYANIDES 

Cyanides  are  produced  on  a  commercial  scale  by  several  methods, 
and  a  large  number  of  patents  which  have  been  put  into  practice  are 
described  in  chemical  literature.  Much  energy  and  money  have  been 
expended  in  fruitless  search  for  processes  of  cheap  production  of 
cyanides.  In  1843  Langlois  *  showed  that  by  passing  ammonia  gas 
over  white-hot  coke  or  charcoal,  some  ammonium  cyanide  is  formed. 
This  reaction  has  been  the  base  of  a  patent  to  Lange  and  Emanuel,f 
in  which  the  yield  is  improved  by  mixing  hydrogen  and  nitrogen  or 
deoxidized  air  with  the  ammonia  :  — 

2  NH3  +  2  C  +  2  H  =  C2(NH4)2. 
C2(NH4)2  +  2  N  =  2  CN(NH4). 

Cyanogen  is  present  in  crude  coal  gas  and  in  some  large  gas  works 
it  is  recovered  by  Bueb's  process,  t  The  gas  is  led  direct  from  the 
tar  extractor  into  a  scrubber  machine  containing  a  ferrous  sulphate 
solution.  The  hydrogen  sulphide  and  ammonia  in  the  gas  react  with 
the  iron  salt  to  form  ferrous  sulphide,  which  in  turn  precipitates  the 
cyanogen  as  an  insoluble  salt  of  iron-ammonium  cyanides;  this  is 
drawn  from  the  machine  as  a  black  mud  suspended  in  the  liquor,  and 
is  filter-pressed.  The  reactions  are  :  — 

FeS04  +  H2S  +  2  NH3  =  2  FeS  +  (NH4)2SO4. 
2  FeS  +  6  NH3  +  6  CN  +  3  H2O  +  5  O  =  (NH4)2Fe2(CN)6 

+  2(NH4)2S04. 

The  solid  cake  is  then  decomposed  with  lime  to  form  calcium 
ferrocyanide,  which,  in  solution,  is  drawn  off  from  the  sludge  and  de- 
composed with  potassium  carbonate  to  yield  potassium  ferrocyanide. 
The  ammonia  is  also  recovered  by  distillation.  If  the  ammonia  is 
first  removed  from  the  crude  gas  by  scrubbing,  it  is  necessary  to  add 
alkali  (Na2CO3)  to  the  copperas  liquor  in  the  cyanogen  scrubber. 
Foulis  §  process  is  based  on  this,  a  sodium  ferrocyanide  being  formed. 

The  recovery  of  cyanides  from  the  spent  oxide  from  the  purifiers 
is  described  on  page  29 1» 

*  Berzelius  Jahresbericht,  22,  84.  t  German  Pat.  No.  122,280. 

t  German  Pat.  No.  100,775.  §  J.  Soc.  Chem.  Ind.,  1893,  511. 

U  289 


290  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

Bunsen  and  Playf  air's  process  *  for  making  cyanides  by  heating 
barium  carbonate  with  powdered  charcoal  in  an  atmosphere  of  dry 
nitrogen  was  not  a  commercial  success.  It  involved  the  reaction  :  — 

BaCO3  +  4  C  +  2  N  =  Ba(CN)2  +  3  CO. 

They  also  showed  that  the  injection  of  heated  air  into  a  furnace 
containing  carbon,  alkaline  earth  oxides,  and  heavy  metals  produces 
cyanide  ;  thus  the  gases  from  blast  furnaces  contain  these  materials, 
and  considerable  attention  has  been  given  to  recovering  cyanides 
from  the  gases  ;  but  as  yet  there  has  been  no  general  introduction  of 
these  methods. 

Raschen's  process  t  is  based  on  the  oxidation  of  sulphocyanide  by 
means  of  nitric  acid  and  atmospheric  air.  It  is  a  continuous  process, 
involving  the  following  reactions  :  — 

NaCNS  +  2  HNO3  =  HCN  +  NaHSO4  +  2  NO. 
2  NO  +  H20  +  3  O  =  2  HNO3. 

The  apparatus  consists  of  a  series  of  earthenware  jars,  connected  by 
earthenware  pipes  and  so  arranged  that  the  liquor  flows  from  near 
the  middle  of  each  jar,  and  passes  to  the  bottom  of  the  next.  The 
gases  from  the  decomposition  contain  prussic  acid  and  much  nitric 
oxide;  they  are  scrubbed  with  water  to  remove  the  nitrogen 
oxides,  and  then  the  prussic  acid  is  absorbed  by  caustic  alkali 
and  the  solution  evaporated  in  vacuum  pans  to  prevent  decom- 
position. 

Ammonium  sulphocyanide  (thiocyanate),  NH4SCN,  is  sometimes 
prepared  by  Tscherniak  and  Giinzburg's  modification  of  Gelis'  pro- 
cess. |  This  depends  on  the  following  reactions  :  — 


1)  CSa  +  2  NH3  =  NH4S2CNH2.     (Ammonium  dithiocarbamate.) 

2)  NH4S2CNH2  =  NH4SCN  +  H2S. 


Carbon  disulphide  and  ammonium  hydroxide  (0.91  sp.  gr.),  in 
proper  proportion  for  reaction  (1),  are  heated  in  an  autoclave  to 
125°  C.,  while  stirring  actively.  The  steam  is  then  cut  off,  but  the 
stirring  continued  until  the  pressure  rises  to  15  atmospheres.  This 
completes  the  first  reaction,  and  the  contents  of  the  autoclave  are 

*  Rep.  British  Assoc.,  1845.     J.  pr.  Chem.,  42  (1847),  397. 
t  U.  S.  Pat.  No.  567,552.     Eng.  Pat.  No.  21,678  (1895). 
J  Dingler's  Polytechnisches  Journal,  245,  214. 


CYANIDES  291 

blown  off  into  a  still,<  which  is  heated  to  110°  C.,  at  which  point  the 
ammonium  dithiocarbamate  is  decomposed.  The  products  of  distil- 
lation are  passed  through  condensers  and  scrubbers  to  collect  volatile 
ammonium  salts  and  carbon  disulphide,  while  the  hydrogen  sulphide 
is  conducted  into  a  gasometer.  The  liquid  in  the  still  contains  am- 
monium sulphocyanide,  and  is  evaporated  in  tin  vessels,  and  crystal- 
lized. 

Sometimes  lime  and  manganese  peroxide  are  added  to  assist  the 
reaction  in  the  autoclave,  in  which  case  calcium  sulphocyanide  is 
formed :  — 

2  CS,  +  2  NH3  +  MnO2  +  CaO  =  Ca(SCN)2  +  MnS  +  S  +  3  H2O. 

Ammonium  sulphocyanide  and  potassium  ferrocyanide  are  now 
largely  obtained  from  the  spent  iron  oxide  from  the  purification  of 
illuminating  gas.  The  spent  oxide  is  first  lixiviated  with  warm  water 
(60°  C.),  until  the  liquor  has  a  density  of  from  1.07  to  1.085.  The 
solution,  containing  ammonium  sulphocyanide  and  other  ammonium 
salts,  is  evaporated  to  1.2  sp.  gr.,  and  cooled,  when  the  associated 
salts  (ammonium  sulphate,  etc.)  crystallize.  The  mother-liquor  is 
further  concentrated,  and  impure  crystals  of  the  sulphocyanide 
separate,  which  are  purified  by  recrystallization.  Ammonium  sul- 
phocyanide is  also  obtained  from  gas-liquor  by  treating  the  non-vola- 
tile residue  from  the  steam  distillation  (see  Ammonia)  with  copper 
and  iron  sulphates,  whereby  cuprous  sulphocyanide  is  formed.  This 
is  washed,  and  treated  with  ammonium  sulphide,  forming  cuprous 
sulphide  and  ammonium  sulphocyanide.  The  latter  is  then  extracted 
with  water. 

Ammonium  sulphocyanide  is  very  soluble  in  water  and  in  alcohol. 
It  is  used  as  a  source  of  other  sulphocyanides,  and  in  dyeing,  to  pre- 
vent the  injurious  action  of  iron  on  the  color. 

The  residue  from  the  lixiviation  is  mixed  with  quicklime  (which 
is  slaked  by  the  moisture  in  the  damp  mass),  and  heated  by  steam 
in  closed  vessels  to  100°  C.  The  lime  decomposes  the  ferric  ferrocy- 
anide and  the  double  iron-ammonium  cyanides,  setting  free  ammonia 
gas,  which  is  absorbed  in  scrubbers,  and  forming  calcium  ferrocyanide, 
which  is  obtained  by  lixiviating  the  mass.  The  solution  of  calcium 
ferrocyanide  is  evaporated,  and  treated  with  the  calculated  amount 
of  potassium  chloride  to  form  the  difficultly  soluble  calcium-potassium 
ferrocyanide,  CaK2Fe(CN)6.  This  is  separated  from  the  mother- 
liquor,  washed,  and  decomposed  with  potassium  carbonate  to  form 
potassium  ferrocyanide. 


292  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

The  reactions  are  :  — 


1)  Fe4  SFe(CN)6J  ,  +  6  Ca(OH)2  =  3  Ca2Fe(CN)6  +  4  Fe(OH)3. 

2)  (NH4)3Fe3  SFe(CN)6J  ,  +'6  Ca(OH)2  = 

3  Ca2Fe(CN)6  +  3  Fe(OH)3  +  3  NHs  +  3  H2O. 

3)  Ca2Fe(CN)6  +  2  KC1  =  CaK2Fe(CN)6  +  CaCl2. 

4)  CaK2Fe(CN)6  +  K2CO3  =  K4Fe(CN)6  +  CaCO3. 


Potassium  ferrocyanide,  K4Fe(CN)6  •  3  H2O,  also  called  yellow 
prussiate  of  potash,  is  made  by  fusing  together  potassium  carbon- 
ate, iron  borings,  and  nitrogenous  organic  matter  of  any  kind  (horn, 
hair,  blood,  wool  waste,  and  leather  scraps).*  The  potash  is  fused 
in  a  shallow  cast-iron  pan,  set  in  a  reverberatory  furnace,  and  the 
organic  matter,  mixed  with  from  6  to  8  per  cent  of  iron  borings, 
is  stirred  in,  in  small  portions  at  a  time,  until  about  Ij  parts  of  the 
mixture  for  each  part  of  potash  have  been  added.  The  temperature 
must  be  kept  high  enough  to  keep  the  mass  perfectly  liquid,  but  not 
hot  enough  to  volatilize  the  cyanogen  salts.  The  reaction  is  violent 
at  first,  and  when  the  liquid  remains  in  quiet  fusion  the  process  is 
ended,  and  the  melt  is  ladled  into  iron  pans  to  cool.  The  mass,  con- 
taining a  number  of  substances  (KCN,  K2CO3,  K2S,  FeS,  metallic 
iron,  carbon,  etc.),  is  broken  up  into  lumps  the  size  of  an  egg,  and 
digested  with  water  at  85°  C.  for  several  hours.  During  this  process 
reactions  take  place  between  the  potassium  cyanide  and  iron  sulphide, 
by  which  the  ferrocyanide  is  formed  :  — 

6  KCN  +  FeS  =  K2S  +  IQFetCNV 

Liebig  explained  the  reactions  during  the  fusion  as  follows  :  part 
of  the  carbon  and  nitrogen  of  the  organic  matter  combine  to  form 
cyanogen  (CN)2,  while  some  of  the  potash  is  reduced  by  the  excess  of 
carbon  to  metallic  potassium,  which  at  once  unites  with  the  cyanogen 
to  form  potassium  cyanide.  The  sulphur  in  the  organic  matter  com- 
bines with  the  iron,  forming  ferrous  sulphide.  Finally,  on  lixiviating, 
the  formation  of  the  ferrocyanide  takes  place.  The  solution  is  evapo- 
rated in  iron  pans  by  the  waste  heat  of  the  furnace,  and  clarified  while 
hot  ;  on  cooling,  the  crude  ferrocyanide  crystallizes,  and  is  purified  by 
recrystallization.  The  mother-liquors  yield  more  impure  salt  on 
further  evaporation. 

*  The  organic  refuse  is  sometimes  partially  charred  in  retorts,  by  which  much 
ammonia  is  driven  off  and  saved.  But  the  yield  of  ferrocyanide  is  then  less,  since 
the  nitrogen  content  of  the  char  is  small. 


CYANIDES  293 

The  calcium  ferrocyanide  liquor  from  gas  purification  (p.  289) 
yields  potassium  ferrocyanide  by  treatment  with  potassium  carbonate, 
filtering,  and  evaporation  to  crystallization. 

Potassium  ferrocyanide  forms  splendid  large  lemon-yellow  crys- 
tals, having  3  molecules  of  crystal  water,  which  it  gives  off  at  100°  C., 
and  is  converted  to  a  white  powder.  It  is  not  poisonous.  It  is 
largely  used  for  making  Prussian  blue  ;  in  calico  printing,  and  in 
dyeing  ;  for  case-hardening  iron  ;  for  making  potassium  cyanide  and 
ferricyanide  ;  and  to  a  small  extent  in  explosives,  and  as  a  chemical 
reagent. 

Barium  sulphocyanide,  Ba(SCN)2,  is  made  by  heating  ammonium 
sulphocyanide  with  barium  hydroxide  solution,  under  slight  pressure. 
Ammonia  distils  off,  and  the  liquid  is  evaporated  to  yield  the  barium 
salt,  Ba(SCN)2  •  2  H2O.  This  is  generally  used  for  making  potassium 
and  aluminum  sulphocyanides,  KSCN  and  A1(CSN)»,  which  are  used 
in  textile  dyeing  and  printing. 

Potassium  ferricyanide,  red  prussiate  of  potash,  K3Fe(CN)6,  is 
usually  made  by  passing  chlorine  gas  into  a  solution  of  the  ferro- 
cyanide, until  ferric  chloride  no  longer  forms  a  precipitate,  only 
producing  a  brown  color  in  the  liquid.  It  may  also  be  made  by 
exposing  the  dry  powdered  ferrocyanide  to  chlorine  until  a  test 
portion,  dissolved  in  water,  gives  nothing  but  a  brown  color  with 
ferric  chloride. 

2  K4Fe(CN)6  +  2  Cl  =  2  KC1  +  2  K3Fe(CN)6. 

Excess  of  chlorine  must  be  avoided,  since  this  forms  a  dirty  green 
precipitate  (Berlin  green)  in  the  solution,  which  cannot  be  removed  by 
filtering. 

Lunge  *  recommends  boiling  the  solution  of  ferrocyanide  with 
lead  peroxide,  while  passing  a  stream  of  carbon  dioxide  through  the 
liquor  :  — 

2  K4Fe(CN)6  +  H2O  +  O  =  2  K3Fe(CN)6  +  2  KOH  ; 

but  the  final  reaction  may  be  written  :  — 
2  K4Fe(CN)6  +  PbO2  +  2  CO2  =  2  K3Fe(CN)6  +  PbCO3  +  K2CO3. 


An  excess  of  carbon  dioxide  is  necessary  to  prevent  decomposi- 
tion of  the  ferricyanide  by  the  lead  oxide  and  alkali. 

A  very  good  product  is  obtained  by  the  action  of  potassium  per- 

*  Dingier'  s  Polytechnisches  Journal,  238,  75. 


294  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

manganate  on  a  mixture  of  calcium  and  potassium  ferrocyanide  solu- 
tions :  — 

3  Ca2Fe(CN)6  +  7  K4Fe(CN)6  +  2  KMnO4  = 

10  K3Fe(CN)6  +  6  CaO  +  2  MnO. 

The  calcium  and  manganese  hydroxides  formed  are  removed  from 
the  solution  by  carbon  dioxide,  and  the  ferricyanide  purified  by 
crystallization. 

Recently,  anodic  oxidation  of  a  ferrocyanide  solution,  to  form 
the  ferricyanide,  has  been  introduced. 

Potassium  ferricyanide  crystallizes  in  blood-red  prisms,  without 
crystal  water,  and  is  very  soluble,  forming  a  solution  of  an  intense 
yellow  color.  With  ferrous  salts,  it  gives  the  blue  pigment,  Turn- 
bull's  blue.  With  ferric  salt,  it  gives  a  brown  coloration,  but  no  pre- 
cipitate. Its  solution,  with  caustic  potash,  is  a  powerful  oxidizing 
liquid,  and  as  such  is  used  in  calico  printing  for  a  "  discharge  "  on 
indigo  and  other  dyes.  It  also  forms  part  of  the  sensitive  coating 
for  "  blue  print  "  papers.  It  has  been  recommended  for  use  with  the 
potassium  cyanide  solution  in  gold  extraction. 

Potassium  cyanide,  KCN,  is  generally  made  by  fusing  the  ferro- 
cyanide with  potassium  carbonate,  until  the  evolution  of  gas  ceases. 
The  following  is  the  reaction  :  — 

K4Fe(CN)6  +  K2CO3  =  5  KCN  +  KCNO  +  CO2  +  Fe. 

The  metallic  iron  separated  sinks  to  the  bottom  of  the  crucible,  and 
the  fused  mixture  of  cyanide  and  cyanate  is  run  off.  The  addition 
of  powdered  charcoal  reduces  part  of  the  cyanate  to  cyanide.  The 
product  is  pure  enough  for  many  purposes.  The  cyanate,  which  is 
sometimes  injurious,  may  be  reduced  by  the  action  of  metallic  zinc 
or  sodium,  or  the  cyanide  may  be  extracted  with  alcohol,  acetone,  or 
carbon  disulphide. 

By  fusing  the  ferrocyanide  with  metallic  sodium,  a  mixture  of 
sodium  and  potassium  cyanides  is  obtained,  which  is  extensively 
employed  in  the  arts  as  "  potassium  cyanide."  The  so-called  "  cyan- 
salt  "  is  made  by  fusing  the  ferrocyanide  with  sodium  carbonate ; 
this  is  cheaper  than  the  pure  potassium  salt. 

Potassium  cyanide  is  also  made  by  fusing  the  dry  ferrocyanide 
in  closed  crucibles,  until  nitrogen  ceases  to  be  given  off.  Carbide  of 
iron  is  formed,  and  sinks  to  the  bottom  of  the  crucible,  if  the  fusion 
is  allowed  to  stand  for  a  considerable  time.  But  the  separation  is 
imperfect,  and  the  product  is  usually  dissolved  in  alcohol  or  acetone, 


CYANIDES  295 

and  the  clarified  solution  heated  in  a  still  to  recover  the  solvent. 
The  product  is  then  heated  until  it  fuses,  and  when  cold,  it  forms  a 
white,  transparent  mass.  Air  must  be  carefully  excluded  during 
the  whole  process,  to  prevent  the  formation  of  cyanate.  The  re- 
action is  •  — 

K4Fe(CN)6  =  4  KCN  +  FeC2  +  N,. 

But  the  product  is  not  entirely  free  from  potassium  carbonate, 
since  it  is  practically  impossible  to  evaporate  a  cyanide  solution 
without  some  decomposition  and  escape  of  the  weak  hydrocyanic 
acid.  The  caustic  potash  thus  formed  then  combines  with  carbon 
dioxide  from  the  air.  Water  cannot  be  used  to  leach  the  iron  car- 
bide residue,  since  the  potassium  cyanide  in  solution  at  once  recom- 
bines  with  the  iron  to  form  ferrocyanide  again. 

Potassium  cyanide  is  made  from  the  sulphocyanide,  by  extract- 
ing the  sulphur  with  zinc  or  lead.*  The  zinc  is  melted  in  a  graphite 
vessel,  and  charcoal  powder  is  spread  over  its  surface.  The  sulpho- 
cyanide is  stirred  into  the  fused  metal  until  the  mass  becomes  a 
thfck  paste,  when  it  is  allowed  to  cool.  It  is  then  systematically 
lixiviated  in  tanks  similar  to  Shank's  apparatus  (p.  97.)  Any  alkali 
sulphide  is  precipitated  by  adding  lead  cyanide.  The  solution  is 
evaporated  in  vacuum,  and  yields  an  impure  product,  containing 
cyanate  and  double  zinc-potassium  cyanide. 

Beilby's  process  f  consists  in  passing  dry  ammonia  gas  through  a 
fused  mixture  of  potassium  carbonate  and  carbon.  A  little  potas- 
sium cyanide  is  added  to  increase  the  fusibility  of  the  charge.  The 
process  is  conducted  in  a  covered  cast-iron  pot,  or  in  a  vertical  retort 
having  revolving  rakes  to  stir  the  charge,  and  the  fumes  pass  to  a 
dust  chamber.  When  the  desired  percentage  of  potassium  cyanide 
has  been  reached  in  the  fused  mass,  the  charge  is  tapped  off  through 
a  strainer  to  retain  suspended  carbon  and  run  direct  into  drums.  A 
similar  method  by  Siepermann  is  worked  in  Germany. 

Castner's  process  involves  the  passing  of  dry  ammonia  gas  over 
metallic  sodium  at  a  temperature  of  350°  C.,  and  immediately  run- 
ning the  sodamide  thus  formed  through  layers  of  red-hot  charcoal ; 
or  a  fusion  of  sodium  cyanide  and  metallic  sodium  is  mixed  with 
powdered  charcoal,  and  ammonia  is  passed  through  it. 

NH3  +  Na  =  NaNH2  +  H. 
NaNH2  +  C  =  NaCN  +  2  H. 

*  J.  Soc.  Chem.  Ind.,  1892,  14. 

f  Ibid.,  1892,  747,  1004.  Eng.  Pat.  No.  4820,  1891. 


296  OUTLINES   OF    INDUSTRIAL   CHEMISTRY 

Potassium  cyanide  comes  in  commerce  as  white  lumps  or  powder, 
very  soluble  in  water  and  having  alkaline  reaction.  It  smells  some- 
what like  bitter  almond  oil,  owing  to  the  prussic  acid  liberated  from 
it  by  the  action  of  carbon  dioxide  and  moisture  in  the  air.  On  stand- 
ing, or  when  warmed,  its  aqueous  solution  decomposes,  yielding  am- 
monia and  potassium  formate :  KCN  +  2  H2O  =  NH3  +  HCOOK. 
When  heated  with  reducible  substances,  it  has  strong  reducing  prop- 
erties ;  hence  its  use  as  a  flux  in  assaying  and  metallurgy.  It  is  ex- 
tensively used  in  electroplating  solutions,  forming  soluble  double 
cyanides  with  gold,  silver,  copper,  and  other  metals,  in  which  the 
metal-ion  concentration  is  very  small,  thus  giving  favorable  condi- 
tions for  a  good  deposit.  Its  largest  use  is  for  the  recovery  of  gold 
from  low-grade  ores,  and  tailings  of  other  reduction  processes  (p. 
631).  A  weak  solution  is  used  to  dissolve  the  gold,  forming  aurous 
potassium  cyanide,  AuCN  •  KCN.  Formerly  it  was  employed  in 
photography  to  "  fix  "  the  image  of  negatives  and  prints,  but  has 
now  been  displaced  by  sodium  thiosulphate  ("  hypo  ").  Potassium 
cyanide  is  extremely  poisonous,  both  when  taken  internally  and  when 
introduced  into  the  blood  directly. 

The  commercial  salt  usually  contains  cyanate  and  carbonate, 
and  is  sold  in  several  grades ;  the  pure  potassium  salt  contains  about 
40  per  cent  of  cyanogen,  while  sodium  cyanide  contains  about  53 
per  cent  cyanogen,  thus  an  impure  potassium  cyanide  containing 
sodium  cyanide  may,  by  analysis  based  on  the  cyanogen  content, 
appear  to  be  100  per  cent  pure,  or  even  higher,  if  estimated  as  KCN. 
Commercial  grades  may  assay  as  low  as  65  per  cent,  but  95  to  98  per 
cent  is  customary. 

REFERENCES 

The  Cyanide  Industry.  R.  Robine  and  M.  Lenglen.  Trans,  by  J.  A. 
LeClerc,  New  York,  1906. 

Coal  Gas  Residuals.  Frederick  Wagner,  New  York,  1914.  (McGraw- 
Hill  Co.) 


CARBON   BISULPHIDE 


Carbon  disulphide,  €82,  may  be  made  by  passing  sulphur  vapor 
over  coke  or  charcoal,  at  a  red  heat  (higher  temperatures  are  not 
necessary).  This  was  formerly  done  in  iron  or  fire-clay  retorts  * 
heated  from  without,  but  destruction  of  the  retorts  was  rapid.  An 
improved  apparatus  (Fig.  92),  devised  by 
Taylor,  f  makes  use  of  electrical  heating,  which 
localizes  the  heat  within  the  retort  and  makes 
it  possible  to  keep  the  walls  relatively  cool, 
thus  decreasing  the  wear  and  tear.  Sulphur 
is  put  into  the  chamber  (Z)  and  partly  sur- 
rounds the  carbon  electrodes  (E).  Fragments 
of  coke  (J )  fill  the  space  between  the  electrodes 
and  are  fed  to  the  furnace  through  (K,  K), 
thus  maintaining  the  continuity  of  electrodes. 
The  shaft  of  the  furnace  is  filled  through  (X) 
with  charcoal  t  (Y).  Crushed  sulphur  is  fed 
through  (V,  V)  and  (R),  filling  the  chambers 
(0)  and  (U).  An  alternating  current  is  ap- 
plied through  the  electrodes,  the  sulphur  in 
(Z)  melts,  and  rising  around  the  electrodes 
cuts  off  the  contact  more  or  less,  and  the  fur- 
nace is  partly  self -regulating.  The  heat  zone  is  at  the  top  of  the 
melted  sulphur  layer,  and  the  vapor  rises  through  the  charcoal  (Y), 
which  has  become  sufficiently  hot  to  form  carbon  disulphide,  the 
vapor  passing  through  (P)  to  the  condensers.  The  furnaces  are  41 
feet  high  by  16  feet  in  diameter. 

The  crude  carbon  disulphide  is  impure  and  has  a  very  offensive 
odor.  It  is  purified  to  remove  hydrogen  sulphide,  free  sulphur,  etc., 
by  redistillation  in  a  steam-heated  still  with  a  little  caustic  soda,  or 
anhydrous  copper  sulphate,  in  the  still ;  or  by  washing  with  lime- 
water,  followed  by  redistillation  over  a  solution  of  lead  acetate. 

Carbon  disulphide  is  a  pale  yellow,  or  colorless,  heavy,  mobile 
liquid,  having  a  fetid  odor  when  impure,  boiling  at  46°  C.,  and  ex- 


FIG.  92. 


*  J.  Soc.  Chem.  Ind.,  1889,  93. 

t  Trans.  Am.  Electro.  Chem.  Soc.,  1  (1902),  115 ;  2  (1902),  185. 
Ind.,  1902,  353,  979,  1236. 

J  Necessary  to  secure  rapid  reaction  with  the  sulphur. 

297 


J.  Soc.  Chem. 


298  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

tremely  volatile  at  ordinary  temperatures.  Its  vapors  inflame  at 
149°  C.,  are  very  heavy,  and  are  poisonous  when  breathed.  It  is  sent 
to  market  in  sheet  iron  cans,  or  drums,  and  is  regarded  as  dangerous 
freight  because  of  its  extreme  volatility,  and  the  explosive  nature  of 
its  vapor  when  mixed  with  air.  When  burned,  it  produces  large  quan- 
tities of  suffocating  gases  (CO2,  802).  It  is  only  slightly  soluble  in 
water,  but  mixes  well  in  all  proportions  with  ether,  benzene,  alcohol, 
and  many  oils.  It  dissolves  sulphur,  phosphorus,  iodine,  camphor, 
wax,  tar,  resins,  rubber,  and  nearly  all  oils  and  fats.  Hence  its  use 
as  a  solvent  and  extractive  agent  is  extensive.  It  is  also  used  as  a 
disinfectant;  as  a  germicide  and  insecticide  in  agriculture,  and  in 
museums  and  herbariums ;  in  refrigerating  machines  ;  for  exterminat- 
ing moles,  rats,  woodchucks,  and  other  burrowing  animals ;  in  the 
manufacture  of  rubber  cement ;  in  making  cyanides  and  carbon  tetra- 
chloride ;  and  in  organic  preparation  work. 


CARBON  TETRACHLORIDE 

Carbon  tetrachloride  is  made  by  passing  a  mixture  of  carbon  di- 
sulphide  vapor  and  chlorine  through  a  red-hot  porcelain  tube.*  A 
mixture  of  sulphur  chloride,  S2C12,  and  carbon  tetrachloride  results, 
which  is  treated  with  milk  of  lime,  and  digested  with  potash,  and  the 
tetrachloride  distilled.  Or  dry  chlorine  may  be  led  into  carbon 
disulphide  containing  a  little  iodine  in  solution,  f  The  tetrachloride 
is  distilled  off,  and  washed  with  alkali,  to  remove  iodine  and  sulphur 

chloride. 

+  6  Cl  =  CC14  +  S2C12. 


Carbon  tetrachloride  is  a  heavy,  colorless  liquid,  boiling  at  76°  C. 
It  is  a  good  solvent  for  many  substances,  and  may  be  used  instead  of 
chloroform  or  carbon  disulphide  for  extractions  and  is  less  poisonous 
than  the  latter.  At  temperatures  but  little  above  its  boiling-point, 
it  dissociates  and  hydrolyzes  in  the  presence  of  water,  forming 
chlorine  and  hydrochloric  acid.  This  limits  its  uses  as  a  solvent. 
It  is  not  inflammable  and  is  used  in  some  types  of  fire-extinguishers. 

*  Kolbe,  Annalen  der  Chemie  und  Pharmacie,  45,  41  ;    54,  145. 
t  Lever  and  Scott,  English  Patent  No.  18,990,  1889. 


MANGANATES  AND  PERMANGANATES 

Sodium  manganate,  Na2MnO4,  is  made  by  mixing  sodium  nitrate 
or  caustic  soda  solution  with  powdered  pyrolusite,  or  manganese 
oxides,  evaporating  to  dryness,  and  calcining  the  mass  at  a  red  heat, 
with  access  of  air,  in  shallow  vessels.  The  following  is  the  reaction 
involved :  — 

MnO2  +  2  NaOH  +  O  =  Na2MnO4  +  H2O. 

The  product  of  the  fusion  is  a  dull  green,  porous  mass,  which,  if 
lixiviated,  yields  a  green  solution  of  the  manganate.  But  this  is 
unstable,  and  if  exposed  to  the  air,  or  treated  with  an  acid,  or  boiled, 
the  manganate  is  converted  into  permanganate :  — 

3  Na2MnO4  +  2  H2O  =  2  NaMnO4  +  4  NaOH  +  MnO2. 

In  alkaline  solution,  however,  the  manganate  is  more  stable. 

Sodium  manganate  is  a  powerful  oxidizing  agent,  and  is  used  as  a 
disinfectant.  It  is  also  converted  to  the  permanganate,  and  sold  in 
solution  as  "  Condy's  liquid  "  for  disinfecting  purposes.  Sodium  per- 
manganate does  not  crystallize  well. 

Potassium  manganate,  K2MnO4,  is  very  similar  to  the  sodium  salt, 
and  is  made  in  the  same  way.  It  is  chiefly  used  in  preparing  the 
permanganate,  KMnO4,  which  crystallizes  very  well.  This,  being 
easily  purified,  and  stable  when  crystallized,  is  the  most  important 
permanganate  of  commerce.  It  was  formerly  made  by  decomposing 
potassium  manganate  with  sulphuric  acid,  carbon  dioxide,  or  chlorine, 
followed  by  recrystallization. 

3  K2MnO4  +  2  H2SO4  =  2  KMnO4  +  2  K2SO4  +  MnO2  +  2  H2O. 
3  K2MnO4  +  2  CO2  =  2  KMnO4  +  2  K2CO3  +  MnO2. 
2  K2MnO4  +  C12  =  2  KMnO4  +  2  KC1. 

It  is  now  made  by  anodic  oxidation  of  the  manganate  (made  as  above) 
in  alkaline  solution,  the  cell  having  a  porous  diaphragm :  — 

2  K2Mn04  +  O  +  H20  =  2  KOH  +  2  KMnO4. 

The  permanganate  crystallizes  and  settles  to  the  bottom  of  the  anode 
compartment,  from  which  it  is  "  fished  "  out  at  intervals.  The  caustic 
potash  formed  migrates  to  the  cathode,  whence  it  is  continuously 

299 


300  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

removed  and  returned  to  the  manganate  fusion.  By  this  process  no 
foreign  substances  are  introduced,  and  the  conversion  of  the  man- 
ganate to  permanganate  is  complete. 

Potassium  permanganate  forms  deep  purple,  prismatic  crystals, 
which  dissolve  in  16  parts  of  cold  water.  The  solution  has  a  power- 
ful oxidizing  action,  and  can  only  be  filtered  on  glass-wool  or  asbestos. 
When  mixed  with  organic  matter,  the  dry  powder  is  subject  to  spon- 
taneous combustion,  and  forms  explosive  mixtures  with  easily  oxidiz- 
able  substances.  It  is  used  as  a  disinfectant ;  in  bleaching  and  dye- 
ing ;  for  coloring  wood  a  deep  brown ;  for  purifying  ammonia  and 
carbon  dioxide  gases ;  and  in  medicine. 


PART    II 
ORGANIC   INDUSTRIES 


DESTRUCTIVE  DISTILLATION  OF  WOOD 


WOOD  consists  mainly  of  cellulose  (CeHioOs),^  with  its  incrusting 
layer  of  lignin,  and  of  sap,  containing  water,  resins,  tannins,  coloring 
matter,  and  mineral  salts.  Air-dried  wood  contains  15  to  20  per 
cent  of  moisture.  When  heated  in  closed  retorts,  away  from  the  air, 
the  cellulose  and  ligneous  matter  decompose,  after  the  moisture  is 
expelled,  and  a  complex  series  of  reactions  occurs,*  by  which  a  great 
number  of  substances  are  formed.  The  crude  products  are  gases, 
thin  liquids,  viscous  liquids  or  tar,  and  charcoal.  When  wood  is  car- 
bonized in  pits  (p.  35),  the  volatile  products  go  to  waste  ;  by  the  use 
of  retorts,  the  valuable  liquid  distillates  and  tar  are  saved;  the 
gases  evolved  are  mainly  hydrogen,  methane,  ethane,  ethylene,  carbon 
monoxide,  and  carbon  dioxide  ;  they  have  no  value  for  illuminating, 
and  are  burned  under  the  retorts,  thus  economizing  fuel. 

When  wood  is  heated  in  retorts,  the  moisture  is  driven  out,  but 
no  decomposition  occurs  until  the  temperature  approaches  160°  C.  ; 
between  160°  and  175°  C.,  a  thin,  watery  distillate,  called  "pyroligneous 
acid,"  is  formed;  above  275°  C.,  the  yield  of  gaseous  products  be- 
comes marked,  and  between  350°  and  450°  C.,  liquid  and  solid  hydro- 
carbons are  principally  formed.  Above  this  last  temperature,  little 
change  occurs,  and  charcoal,  containing  the  mineral  ash,  remains  in 
the  retort. 

The  pyroligneous  acid  contains  the  important  distillates,  methyl 
alcohol  and  acetic  acid,  together  with  acetone,  methyl  acetate,  phenols, 
ketones,  and  other  substances.  The  tar  contains  aromatic  hydro- 
carbons and  paraffines.  Its  most  valuable  constituent  is  the  creosote 
oil,  containing  guaiacol,  creosol,  and  other  phenols  of  high  molecular 

*  Zeit.  angew.  Chem.,  1909  (22),  1205. 
301 


302 


OUTLINES  OF   INDUSTRIAL   CHEMISTRY 


weight.     A  comparatively  small  amount  of  phenol  or  carbolic  acid  is 
present,  however. 

The  proportion  of  gaseous  products  to  liquid  distillate  and  char- 
coal is  affected  by  the  method  of  heating;  rapid  heating  to  a  high 
temperature  increases  the  quantity  of  gas;  by  distillation  at  a  low 
temperature,  the  yield  of  pyroligneous  acid,  tar,  and  charcoal  is  larger. 
The  variety  of  wood  used  affects  the  amount  of  acid  and  tar ;  decidu- 
ous trees,  especially  birch,  oak,  and  beech,  are  preferred ;  coniferous 
woods  yield  less  acid,  but  afford  a  tar  containing  much  resin  and 
turpentine.  The  yield  of  acid  and  tar  is  increased  by  the  rapid  re- 
moval of  the  vapors  from  the  retort. 

Wood  is  distilled  in  various  kinds  of  kilns  or  retorts.  If  charcoal 
is  the  only  product  in  view,  the  carbonization  may  be  done  in  "  pits  " 
or  kilns  (p.  35),  and  the  volatile  products  go  to  waste.  Masonry 
kilns  of  large  capacity  (15  to  90  cords  at  a  charge)  are  often  used ; 
the  necessary  heat  may  be  derived  from  combustion  of  part  of  the 
charge  itself,  or  from  an  external  fire  whose  combustion  gases  pass 
into  the  kiln,  or  through  flues  in  its  walls. 

When  the  volatile  products  are  to  be  saved  boiler-plate  iron  retorts, 
externally  heated,  are  employed;  these  may  be  either  stationary  or 

movable,  and  of  large  or  small 
capacity.  Small  horizontal  cyl- 
inders (Fig.  93,*  A),  holding 
about  1  or  1 J  cords  at  a  charge, 
are  usually  set  two  in  a  bench, 
over  a  common  furnace.  Each 
retort  connects  with  a  separate 
condenser  (C)  by  the  copper 
pipe  (B) ;  a  pipe  (D)  carries  the 
uncondensed  gases  to  the  grate  where  they  are  burned  under  the  re- 
torts. The  wood,  cut  to  proper  length,  is  rapidly  filled  into  the  retort, 
which  is  still  hot  from  the  previous  charge,  the  door  is  closed  and 
luted  and  distillation  begins  at  once.  After  some  12  hours,  the  hot 
charcoal  is  rapidly  drawn  into  an  iron  box  to  cool  out  of  contact 
with  the  air,  and  the  retort  at  once  recharged. 

For  larger  output,  horizontal  oven-retorts  (Fig.  94)  are  used.  These 
are  rectangular  iron  boxes,  into  which  several  steel  cars,  each  loaded 
with  2  to  4  cords  of  wood,  are  run  at  one  time,  and  the  carbonization 
carried  on  for  24  hours.  Thus  charges  of  10  to  20  cords  of  wood  at 
a  time  are  expeditiously  handled.  When  carbonization  is  finished, 

*  J.  Soc.  Chem.  Ind.,  1897,  667  and  722  (M.  Klar). 


FIG.  93. 


DESTRUCTIVE    DISTILLATION   OF   WOOD 


303 


the  doors  at  each  end  of  the  retort  are  opened,  and  a  string  of  newly 
loaded  cars  pushed  in,  which  also  shoves  out  the  cars  carrying  the  hot 


FIG.  94. 

charcoal  from  the  previous  charge,  into  a  large  iron  box  or  cooler, 
placed  directly  opposite,  where  they  cool  out  of  contact  with  the  air. 
This  transfer  and  introduction  of  a  new  charge  requires  only  a  few 
minutes,  so  these  retorts  are  practically  continuous  in  action  and  the 
loss  of  charcoal  by  combustion  is  small.  This  system  consumes  less 
fuel,  and  has  lower  labor  and  repair  costs  for  a  given  output  than 
the  small  retorts. 

Movable  retorts  are  vertical  boiler-plate  cylinders  (Fig.  95  *)  so 
arranged  that  the  retort  (A),  filled  with  wood  and  with  cover  luted 
on,  is  lowered  by  a  crane  into  the  furnace; 
when  carbonization  is  finished,  the  retort 
containing  the  charcoal  is  lifted  out  to  cool 
unopened,  while  another  charged  with  wood 
is  put  into  its  place.  Connection  with 
the  condenser  is  made  by  a  copper  swing- 
pipe  (B),  clamped  to  the  vent  on  the  top  of 
the  retort.  Each  cylinder  holds  one  cord 
of  wood,  and  as  it  is  packed  cold,  a  com- 
plete filling  of  the  space  is  possible.  The 
labor  cost  for  this  type  is  less  than  for 
small  horizontal  retorts,  but  the  wear  and 
tear  on  the  furnace  and  retorts  from  the 
frequent  moving  and  cooling  is  great;  the  original  cost  of  plant  is 
also  higher. 

Coniferous  woods  are  often  distilled  in  retorts  into  which  super- 
heated or  free  steam  is  introduced,  preliminary  to  the  distillation 
proper.  Thus  the  turpentine  and  much  rosin  are  driven  out  at  tem- 

*  J.  Soc.  Chem.  Ind.,  1897,  668. 


FIG.  95. 


304  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

peratures  below  that  at  which  the  cellulose  is  decomposed.  Then  by 
raising  the  heat  of  the  retort,  true  destructive  distillation  follows, 
yielding  wood  vinegar,  tar,  and  charcoal.  Many  plants  for  distilling 
fat  pine,  "  light  wood,"  have  been  erected  in  this  country,  but  not 
always  with  satisfactory  results.  Considerable  wood  turpentine  is 
produced,  the  yield  being  10  to  20  gallons  of  crude  turpentine  per  cord 
of  "  light  wood,"  but  the  odor  and  color  are  often  not  satisfactory. 

Extraction  processes,  depending  on  the  use  of  solvents  for  both 
turpentine  and  rosin,  such  as  carbon  disulphide  or  carbon  tetrachloride 
or  turpentine  itself,  have  been  patented.  The  extracted  chips  are 
steamed  to  recover  the  solvent,  but  the  losses  are  so  large  that  the 
future  of  these  methods  is  uncertain.  The  extracted  chips  are  suitable 
for  wood  pulp,  or  they  may  be  distilled  for  pyroligneous  acid  and  tar. 
By  treating  the  chipped  wood  with  caustic  soda  liquor  and  steaming, 
the  turpentine  can  be  distilled  off,  while  the  rosin  dissolves  in  the  alka- 
line liquor.  When  drawn  off  and  acidified,  the  rosin  is  precipitated. 

Pyroligneous  acid  or  crude  "  wood  vinegar  "  is  a  reddish  brown 
liquid  with  strong  acid  reaction  and  empyreumatic  odor  due  to  fur- 
furol  in  part.  It  averages  5  to  10  per  cent  acetic  acid,  1.5  to  3  per 
cent  methyl  alcohol,  and  0.1  to  0.2  per  cent  acetone ;  its  specific  gravity 
varies  from  1.020  to  1.050.  A  small  amount  is  used  directly  for  mak- 
ing an  impure  iron  acetate,  sold  as  "  pyrolignite  of  iron  " ;  but  it  is 
usually  worked  for  methyl  alcohol  and  acetic  acid. 

By  neutralizing  pyroligneous  acid  directly  with  milk  of  lime  and 
distilling,  a  raw  wood  spirit  is  collected  as  distillate,  while  calcium 
acetate  solution  remains  in  the  still,  which  on  evaporation  to  dryness 
yields  so-called  "  brown  acetate  of  lime,"  averaging  about  67  per  cent 
of  calcium  acetate.  During  the  evaporation,  tar  separates  as  a  scum, 
which  is  skimmed  off.  The  method  is  not  much  used  at  present. 

By  distilling  pyroligneous  acid  in  a  copper  still,  the  tar  is  left  and 
a  purified  "  wood  vinegar  "  obtained,  containing  acetic  acid,  methyl 
alcohol  (wood  spirit),  methyl  acetate,  acetone,  acetaldehyde,  etc., 
and  traces  of  tar,  empyreumatic  matter,  etc.  This  is  neutralized  with 
lime,  precipitating  many  of  the  impurities;  the  clarified  solution  is 
then  rectified  in  a  column  still,  yielding  wood  alcohol  of  about  82  per 
cent.  The  solution  in  the  still  yields  on  evaporation  to  dryness 
"  gray  acetate  of  lime,"  averaging  80  per  cent  calcium  acetate.  The 
tarry  matter  decomposes  during  the  drying. 

The  raw  wood  alcohol  is  further  purified  by  diluting  with  water 
until  the  oily  matters  (ketones,  aldehydes,  etc.)  precipitate,  as  shown 


DESTRUCTIVE   DISTILLATION  OF  WOOD  305 

by  the  milky  appearance.  On  standing  several  days,  the  oils  rise  to 
the  top  and  are  skimmed  off;  then  the  alcoholic  solution  is  again 
distilled  in  a  fractionating  still,  until  the  concentration  is  about  95 
per  cent  alcohol;  the  product  is  known  as  wood  spirit  or  methyl 
alcohol.  By  filtering  through  charcoal,  the  color  and  unpleasant 
odor  can  be  largely  removed.  Treatment  with  caustic  lime  and  re- 
distillation yields  alcohol  of  99  per  cent,  or  higher,  concentration; 
but  this  does  not  remove  the  acetone. 

The  wood  spirit  may  be  purified  from  acetone  by  treatment  with 
caustic  soda  and  iodine,  producing  a  precipitate  of  iodoform  with  the 
acetone.  Or  calcium  chloride  is  added  to  combine  with  the  methyl 
alcohol  and  form  a  crystallized  solid,  stable  at  100°  C.,  from  which 
the  acetone  is  distilled  off;  then  by  adding  hot  water  and  heating  to 
100°  C.,  or  over,  the  alcohol  is  distilled  off  and  rectified. 

Commercial  methyl  alcohol  is  often  slightly  yellowish  in  color 
and  frequently  has  a  disagreeable  odor.  It  is  much  used  as  a  solvent 
in  varnish  making,  for  which  purpose  the  presence  of  acetone  is  desir- 
able ;  for  making  formaldehyde ;  for  mixing  with  ethyl  alcohol  to  pre- 
pare "  denatured  ethyl  alcohol  "  or  "  methylated  spirit  "  (p.  460). 

Acetone,  when  recovered  from  wood  spirit,  is  generally  distilled 
from  the  calcium  chloride  compound  with  the  methyl  alcohol.  It  is, 
however,  more  commonly  made  by  the  dry  distillation  at  290°  to 
300°  C.,  of  calcium  acetate :  — 

Ca(C2H3O2)2  =  CaCO3  +  CH3  —  CO  —  CH3. 

The  product  obtained  by  either  of  the  above  methods  is  crude ;  sodium 
bisulphite  is  added,  and  forms  a  double  salt  with  the  acetone,  which 
is  purified  by  recrystallization  from  aqueous  solution.  This  salt  is 
decomposed  by  heating  with  sodium  carbonate  solution,  liberating 
the  acetone,  which  distils  off  pure.  Or  the  crude  acetone  is  neutral- 
ized with  lime,  settled,  and  the  supernatant  liquid  diluted  with  water 
and  rectified  in  a  column  still,  yielding  a  pure  acetone  distillate  and 
an  oily  residuum  called  acetone  oil  which  finds  some  use  for  solvent 
and  denaturizing  purposes. 

A  method  for  making  acetone  devised  by  Dr.  E.  R.  Squibb  * 
consists  in  passing  acetic  acid  vapor  through  a  rotating  iron  cylinder, 
heated  to  about  500°-600°  C.,  and  containing  pumice  stone  with  pre- 
cipitated barium  carbonate :  — 

=  H2O  +  CH3  —  CO  —  CH3  +  CO2. 

*  J.  Am.  Chem.  Soc.,  17,  187. 


306  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

The  barium  carbonate  acts  as  a  contact  body,  since  the  temperature 
is  always  above  that  at  which  barium  acetate  decomposes.  The  vapors 
from  the  still  pass  to  a  fractional  condenser  to  remove  water  and  acetic 
acid;  the  acetone  condenses  in  a  second  condenser. 

Acetone  is  a  colorless  mobile  liquid,  having  a  peculiar  odor  and 
unpleasant  taste;  its  specific  gravity  is  0.797  at  15°  C.  and  should 
not  exceed  0.802  in  the  commercial  product.  It  boils  at  56.3°  C.,  and 
mixes  with  water  in  all  proportions ;  is  an  excellent  solvent  for  many 
resins,  gums,  fats,  nitrated  cellulose,  and  other  substances.  It  is  used 
in  the  manufacture  of  celluloid,  smokeless  powders,  chloroform,  iodo- 
form,  sulphonal,  for  extracting  resin  from  crude  rubber,  and  for 
denaturizing  ethyl  alcohol. 

Commercial  acetic  acid  is  prepared  from  gray  or  brown  acetate  of 
lime  *  (p.  304)  by  distilling  with  strong  hydrochloric  or  sulphuric 
acid.  In  the  hydrochloric  acid  process,  copper  stills  heated  by  steam 
coils  are  used;  free  steam  can  also  be  blown  into  the  charge.  The 
acetic  acid  distils  over,  leaving  calcium  chloride  in  the  still.  The 
acid  is  a  slightly  colored  liquid  containing  from  30  to  50  per  cent  of 
anhydrous  acid,  according  to  the  strength  of  the  hydrochloric  acid 
used.  It  may  be  further  purified  by  distilling  again  over  a  little 
potassium  permanganate,  and  filtering  through  fresh  charcoal. 

The  sulphuric  acid  process  is  more  commonly  used  at  present; 
the  still  is  made  of  cast-iron  (Fig.  96  |)  with  a  scraping  device  inside 
to  break  up  the  solid  mass  which  forms  in 
the  still,  and  facilitate  the  escape  of  the  acetic 
acid.  The  stills  are  heated  by  direct  fire.  A 
dust  chamber  should  be  placed  between  the 
still  and  the  copper  worm  condenser.  Owing 
to  secondary  reactions,  some  sulphuric  acid 
is  reduced,  contaminating  the  product  with 
sulphur  dioxide,  and  necessitating  the  use  of 

some  excess  of  sulphuric  acid  in  the  still.  Von  Linde  employs  vacuum 
in  the  still,  whereby  the  temperature  is  lowered  sufficiently  to  permit 
steam  heat  to  be  used  for  the  distillation,  and  secondary  reactions 
are  much  reduced. 

Behrens'  process  consists  in  dissolving  the  calcium  acetate  in 
acetic  acid,  and  then  decomposing  the  solution  with  sulphuric  acid, 
whereby  the  reaction  takes  place  at  lower  temperature. 

*  Brown  acetate  is  calcined  at  230°  C.,  to  destroy  tarry  matter  before  use  in 
this  way. 

t  After  Klar,  Technologic  der  Holzverkohlung. 


DESTRUCTIVE   DISTILLATION   OF  WOOD  307 

The  distillate  contains  about  75  per  cent  anhydrous  acetic  acid 
and  usually  a  little  sulphur  dioxide.  This  acid  is  then  rectified  in  a 
large  copper  column  still,  heated  by  a  steam  coil.  The  plates  in  the 
column  are  often  porcelain  or  earthenware ;  the  condensers  are  usually 
copper  worms.  If  air  is  excluded  from  the  apparatus,  there  is  little 
attack  on  the  copper  by  the  acid ;  but  this  necessitates  the  immediate 
refilling  of  the  still  after  each  charge  has  been  worked  off.  If  the 
operation  is  to  be  discontinued,  the  still  and  condensers  should  be 
thoroughly  washed  out  with  water.  When  starting  each  distillation, 
the  heating  should  be  slow,  to  allow  the  sulphur  dioxide  to  pass  off 
before  the  acetic  acid  begins  to  distil. 

According  to  the  amount  of  cooling  water  admitted  to  the  frac- 
tional condenser,  a  clear  colorless  liquid  containing  from  80  to  99 
per  cent  of  anhydrous  acid  can  be  obtained;  it  contains  traces  of 
empyreumatic  matter,  which  can  be  removed  by  gentle  heating  with 
potassium  permanganate  in  an  earthenware  vessel,  and  redistilling 
in  a  copper  still,  with  an  earthenware,  or  pure  silver,  worm  condenser. 
The  residues  from  the  several  distillations  are  collected  together  and 
redistilled  to  recover  as  much  as  possible  of  the  acetic  acid  in  them. 
The  final  tarry  residues  are  burned. 

By  distilling  the  pyroligneous  acid,  without  neutralization,  in  a 
copper  still,  most  of  the  methyl  alcohol  passes  over  before  the  acetic 
acid ;  by  collecting  the  distillate  until  its  specific  gravity  is  about 
1.000,  a  crude  "  wood  spirit  "  is  separated.  If  the  acetic  acid  vapors 
following  are  passed  into  a  solution  of  soda,  a  solution  of  sodium 
acetate  is  obtained.  This  is  evaporated  until  only  a  fused  mass  of 
sodium  acetate  remains,  which  is  heated  to  nearly  300°  C.,  at  which 
point  the  sodium  acetate  is  stable  but  the  impurities  are  decomposed. 
The  fused  salt  is  dissolved  in  water,  the  solution  filtered  and  evaporated 
to  crystallize.  The  process  may  be  repeated  for  further  purification. 

If  the  distillation  of  the  pyroligneous  acid  be  continued  after  the 
methyl  alcohol  has  passed  over,  the  distillate,  collected  between  100° 
and  120°  C.,  is  called  "  wood  vinegar  " ;  it  is  dilute  and  still  retains 
some  empyreumatic  matter,  but  is  somewhat  employed  technically. 
It  is  generally  neutralized  with  lime  or  soda  to  yield  acetates. 

Glacial  acetic  acid  is  the  nearly  anhydrous,  99  to  100  per  cent 
acid,  which  crystallizes  if  cooled  to  16.5°  C.  It  may  be  made  from 
fused  sodium  acetate,  by  distilling  with  strong  sulphuric  acid  at  120°  C. 
The  residue  from  the  still  is  sodium  sulphate  and  may  be  used  to 
decompose  calcium  acetate  in  solution,  to  prepare  more  sodium 
acetate. 


308  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

Common  acetic  acid  is  found  in  commerce  as  a  slightly  colored 
liquid  of  various  strengths  :  ordinary  No.  8  has  a  specific  gravity  about 
1.040  (8°  Tw.)  and  contains  approximately  30  per  cent  anhydrous 
acid ;  it  is  used  in  preparing  acetates,  in  making  white  lead,  in  textile 
work,  and  in  pharmacy.  Stronger  acid,  containing  50  per  cent  or 
more  of  anhydrous  acid,  is  used  in  preparing  coal-tar  colors  and  calico 
printers'  pastes,  for  preparing  organic  acetates,  and  for  solvent  pur- 
poses. Pure  acetic  acid  from  wood  distillate  may  be  used  for  vinegar, 
but  lacks  the  characteristic  salts  and  flavoring  substances  present  in 
true  fermentation  vinegar  (p.  463). 

Acetates.  —  Aluminum  acetate  in  the  pure  state  is  not  known,  but 
a  solution  of  it  in  acetic  acid,  called  "  red  liquor,"  is  largely  used  in 
dyeing  and  in  calico  printing.  It  is  made  by  dissolving  aluminum 
hydroxide  in  acetic  acid,  or  by  decomposing  lead  or  calcium  acetates 
with  aluminum  sulphate  or  alum :  — 

A12(S04)3  +  3  Pb(C2H3O2)2  =  2  A1(C2H3O2)3  +  3  PbSO4. 

Calcium  acetate  yields  the  best  red  liquor;  that  made  from  lead 
acetate  is  not  entirely  free  from  lead,  which  dulls  the  shade  of  deli- 
cate colors ;  when  made  from  alum,  it  contains  sulphate  of  the  alkali 
metal,  and  decomposes  more  readily  than  when  made  from  aluminum 
sulphate.  Several  basic  aluminum  acetates  are  made  by  adding 
sodium  carbonate  to  the  normal  acetate  solution.  These  deposit 
alumina  on  the  fibre  very  readily. 

Chromium  acetate  finds  some  use  as  a  mordant  in  calico  printing. 
It  is  usually  made  by  dissolving  chromium  hydroxide  in  acetic  acid, 
or  by  decomposing  a  solution  of  chromium  sulphate  or  chrome  alum 
with  lead  or  calcium  acetate.  The  solution  is  violet,  but  becomes 
green  if  heated.  It  may  be  evaporated  to  dryness  without  rendering 
the  salt  insoluble.  Alkalies  and  alkaline  carbonates  yield  no  precipi- 
tate in  the  cold  solution,  but  when  heated,  a  precipitate  of  chromium 
hydroxide  forms. 

Basic  acetates  are  prepared  by  adding  lead  or  calcium  acetate  to 
basic  chromium  sulphate  solution.  Sulphate-acetates  are  also  made 
and  used  as  mordants. 

Calcium  acetate  has  been  mentioned  as  brown  or  gray  acetate  of 
lime  (p.  304).  The  pure  salt,  occasionally  used  as  a  mordant,  is 
made  by  neutralizing  acetic  acid  with  the  theoretical  quantity  of 
lime.  Litmus  does  not  show  the  point  of  neutrality.  The  crystal- 
lized salt,  Ca(C2H3O2)2  •  H2O,  is  very  soluble  in  water. 


DESTRUCTIVE   DISTILLATION   OF  WOOD  309 

Cupric  acetate,  Cu(C2H3O2)2  •  H2O,  is  best  made  by  adding  lead 
acetate  to  copper  sulphate  solution  :  — 

CuS04  +  Pb(C2H3O2)2  =  Cu(C2H3O2)2  +  PbSO4. 

It  may  be  made  by  dissolving  verdigris,  or  copper  carbonate  or  oxide, 
in  acetic  acid.  For  basic  acetates  see  p.  237. 

Ferrous  acetate,  Fe(C2H3O2)2  •  4  H2O,  may  be  prepared  from  cop- 
peras and  lead  or  calcium  acetate;  or  by  dissolving  scrap  iron  in 
acetic  acid.  It  is  quickly  oxidized  in  the  air  to  basic  ferric  acetate. 
"  Pyrolignite  of  iron,"  black  liquor,  or  iron  liquor,  is  made  by  dissolv- 
ing scrap  iron  in  pyroligneous  acid.  It  is  sold  as  a  dirty  olive-brown 
or  black  liquid,  having  a  density  of  about  25°  Tw.,  and  consists  mainly 
of  ferrous  acetate,  with  some  ferric  acetate  and  tarry  matter.  It 
is  used  as  a  mordant  in  dyeing  black  silks  and  cottons,  and  in  calico 
printing. 

Ferric  acetate,  Fe(C2H3O2)3,  made  by  adding  lead  acetate  to  fer- 
ric sulphate,  is  stable  in  cold  solution.  It  forms  basic  salts  when 
treated  with  caustic  soda.  It  was  formerly  used  in  black  silk  dyeing. 

Sodium  acetate,  NaC2H3O2  •  3  H2O,  forms  needle-like  crystals 
which  melt  in  their  crystal  water  when  heated ;  when  anhydrous,  it 
fuses  without  decomposition.  It  is  chiefly  used  for  making  pure 
concentrated  acetic  acid,  in  making  certain  diazo  bodies,  and  as  a 
developer  for  the  azo-dyes,  in  which  the  color  is  made  on  the  fibre. 

Lead  acetate,  Pb(C2H3O2)2  •  3  H2O,  "  sugar  of  lead,"  is  made  by 
dissolving  feathered  lead  by  causing  acetic  acid  to  trickle  over  it  in  the 
presence  of  a  current  of  air.  Or  litharge  is  dissolved  directly  in  acetic 
acid.  If  wood  vinegar  is  used,  the  product  is  "  brown  sugar  of  lead." 
With  an  excess  of  litharge,  basic  acetates  are  formed.  The  normal  salt 
is  very  soluble  in  water,  and  is  used  for  making  other  mordants  and  for 
chrome  yellows.  The  salts  are  poisonous,  and  are  affected  by  the  car- 
bon dioxide  and  hydrogen  sulphide  in  the  air. 

Wood-tar  varies  somewhat  in  character  with  the  kind  of  wood 
carbonized.  It  is  washed  with  hot  water,  or  treated  with  milk  of 
lime,  to  remove  acetic  acid,  and  then  washed  with  very  dilute  sul- 
phuric acid.  Excess  of  water  is  evaporated  by  warming  in  steam- 
jacketed  vessels.  The  tar  is  then  distilled  in  iron  stills,  provided 
with  stirring  apparatus,  the  temperature  being  raised  very  slowly. 
The  distillate  collected  below  150°  C.  is  called  "  light  oil,"  and  is 
chiefly  used  as  a  substitute  for  oil  of  turpentine  in  varnish  and  paints. 
Between  150°  and  250°  C.  the  "  heavy  oil  "  is  collected,  containing 


310  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

creosote,  toluene,  and  paraffine  bodies.  By  stopping  the  distillation 
at  250°  C.,  a  thick,  brownish  liquid  is  obtained,  which  is  used  in 
making  axle  grease,  shoemakers'  wax,  for  lampblack,  and  for  coating 
the  interior  of  casks  and  barrels  to  render  them  impervious  to  liquids. 

The  creosote  oil  is  washed  with  caustic  soda,  and  boiled  in  the  air 
to  oxidize  various  substances  which  it  contains.  The  alkaline  solu- 
tion is  then  acidified  with  sulphuric  acid,  to  precipitate  the  creosote, 
which  is  treated  with  alkali  and  acid  as  before.  It  is  then  distilled 
again,  and  the  distillate,  collected  between  200°  and  220°  C.,  is  the 
commercial  wood-tar  creosote.  It  has  a  strong,  smoky  odor,  is  a 
good  antiseptic,  and  ig  not  poisonous. 

Stockholm  tar  and  pine  tar  are  obtained  by  a  crude  distillation  of 
pitch-pine  or  other  coniferous  wood,  in  heaps,  covered  with  turf. 
These  are  of  different  composition  from  retort  tar,  and  are  mainly 
used  for  tarred  ropes,  with  oakum  for  ship  calking,  and  for  preserving 
timber. 

REFERENCES 

Das  Holz  und  seine  Distillations-Producte.     Dr.  G.  Thenius,  Leipzig,  1880. 

Die  Meiler  und  Retorten  Verkohlung.     Dr.  G.  Thenius. 

Das  Chemische  Technologie  der  Brennstoffe.     F.  Fischer,  Braunschweig, 

1880. 
Die  Verwerthung  des  Holzes  auf  chemischen  Wege.     J.  Bersch,  Leipzig, 

1883. 
Destructive    Distillation.     E.    J.    Mills,    London,    1892.     (Gurney    and 

Jackson.) 
Handbuch  der  Organischen  Chemie.     Victor  Meyer  and  Paul  Jacobson. 

Vol.  I.     Articles  —  "  Essigsaure  "  and  "  Methylalkohol."     Leipzig, 

1893. 

Technologie  der  Holzverkohlung.     M.  Klar,  Berlin,  1910.     (Springer.) 
Handbuch  der  Organischen  Chemie.     F.  Beilstein.     Vol.  1,  3d  ed.     Puri- 
fication of  Wood  Spirit.     Leipzig,  1894.     (L.  Voss.) 
Jahres-Bericht  tiber  die  Leistungen  der  technischen  Chemie :  — 

1892.     1893,  14.     (Distillation  of  Wood.) 
Journal  of  the  Society  of  Chemical  Industry :  — 

1892,  395  and  872.     1897,  667,  722.     M.  Klar.     (Modern  Distillation 

of  Wood.) 


DESTRUCTIVE   DISTILLATION  OF  BONES 

Bones  are  usually  extracted  with  benzine  or  with  carbon  disul- 
phide,  and  the  fatty  matter  used  for  soap  stock.  They  still  contain 
nitrogenous  organic  substances,  and  are  distilled  in  iron  or  clay 
retorts,  similar  to  those  used  in  coal-gas  making  (p.  315),  yielding 
volatile  products,  consisting  of  gases,  ammonium  salts,  and  bone  oil ; 
these  pass  through  condensers,  where  the  water  and  bone  oil  con- 
dense; the  gases  pass  into  a  receiver  containing  sulphuric  acid, 
which  takes  up  the  ammonia  and  its  volatile  compounds ;  the  in- 
flammable gases  are  burned  under  the  retort. 

The  bone  oil  ("  Dippel's  oil  ")  and  aqueous  liquor  collected  under 
the  condensers  are  separated  by  gravity.  The  liquor  contains  am- 
monium carbonate,  cyanide,  sulphocyanide,  and  sulphide,  and  is 
treated  in  the  same  way  as  gas  liquor  (p.  151)  for  the  recovery  of  the 
ammonia.  The  crude  bone  oil  is  a  'dark-colored,  foul-smelling  liquid, 
lighter  than  water.  It  is  redistilled  and  divided  into  numerous 
fractions.  At  high  temperatures  it  also  yields  ammonium  carbonate 
and  cyanide ;  the  thick  tar  remaining  in  the  still  is  the  basis  of  com- 
mercial Brunswick  black. 

The  constituents  of  bone  oil  are  exceedingly  numerous,  but  the 
more  important  are  pyrrol,  C4H4NH ;  pyridine,  CsHsN;  picoline, 
C.5H4(CH3)N;  lutidine  (dimethylpyridine) ;  collidine,  C5H2(CH3)3N; 
and  quinoline,  CeH^  •  CaHaN.  These  have  but  little  technical  use,  but 
are  employed  in  Europe  for  denaturating  alcohol,  and  in  the  prepara- 
tion of  certain  antiseptics.  They  are  closely  related  to  some  of  the 
alkaloids,  but  are  not  as  yet  used  to  prepare  them. 

The  residue  from  the  bone  distillation  is  the  bone-black  or  bone- 
char  of  commerce.  It  forms  about  65  per  cent  of  the  original  weight 
of  the  bones  and  consists  largely  of  calcium  phosphate  and  carbonate, 
impregnated  with  free  carbon.  While  still  hot,  it  is  drawn  from  the 
retort  into  closed  vessels  and  cooled  out  of  contact  with  the  air.  It  is 
largely  used  in  decolorizing  sugar  solutions,  glucose,  glycerine,  oils, 
paraffine,  vaseline,  etc.,  and  in  case-hardening  iron.  It  loses  its  effec- 
tiveness after  a  time,  and  is  then  "  revivified  "  (p.  418).  When  it 
becomes  too  finely  powdered  for  successful  filtration,  it  is  used  as  a 
fertilizer  (p.  165).  . 


311 


ILLUMINATING  GAS 

Illuminating  gas  may  be  made  by  enriching  water  gas  with  oil 
gas,  or  by  the  destructive  distillation  of  coal,  wood,  or  petroleum. 
Goal  gas,  such  as  is  generally  used  at  the  present  time,  was  first 
employed  for  house  illuminating  by  William  Murdock,  in  London,  in 
1792.  It  was  introduced  for  street  lighting  in  London  in  1812,  and 
in  Paris  in  1815.  In  this  country,  the  so-called  water  gas,  enriched 
with  naphtha,  has  largely  replaced  coal  gas  in  many  of  the  large 
cities.  This  has  greater  illuminating  power,  requires  a  smaller  plant 
and  less  labor,  and  ensures  greater  economy  of  working. 

Water  gas  (p.  39)  is  produced  by  the  action  of  steam  on  incandes- 
cent carbon,  according  to  the  reactions  :  — 

C  +  2  H20  =  2  H2  +  CO2. 
=  2  CO. 


It  is  composed  chiefly  of  hydrogen  and  carbon  monoxide,  is  non- 
luminous,  and  has  a  high  heat  value. 

Luminosity  depends  on  the  presence  of  hydrocarbons,  such  as 
ethane,  C2H6,  ethylene  (ethene),  C2H4,  acetylene,  C2H2,  and  benzene, 
CeHe,  and  their  homologues,  the  most  important  of  these  "  illu- 
minants  "  being  ethylene  and  benzene.  In  order  to  render  the  water 
gas  luminous,  it  is  carburetted  with  gases  derived  from  oil,  which  are 
rich  in  illuminants. 

Illuminating  water  gas  .  is  now  made  by  two  general  methods  : 
(a)  the  carburetted  gas  is  made  in  one  operation  ;  (6)  non-luminous 
gas  is  prepared,  and  then  carburetted  by  a  second  process.  The  first 
method  is  most  successfully  carried  out  by  the  Lowe  process.  The 
generator  (Fig.  97)  is  filled  with  anthracite  coal  or  coke,  which  is 
brought  to  incandescence  by  a  blast  of  air.  The  gases  from  the 
generator,  at  this  time  consisting  mainly  of  carbon  monoxide  and 
nitrogen,  enter  at  the  top  of  the  carburettor,  a  circular  chamber 
lined  with  firebrick,  and  containing  a  "  checker-work,"  of  the  same 
material  ;  while  passing  down  through  this,  the  producer  gas  (p.  41) 
is  partly  burned  by  an  air  blast  which  enters  the  apparatus  near  the 
top,  and  the  checker-work  is  heated  white  hot.  The  gases  pass  on 
to  the  "  superheater,"  a  taller  chamber,  also  filled  with  checker-work. 
At  the  bottom  of  this  an  air  blast  is  introduced  to  complete  the 
burning  of  the  producer  gas  and  to  raise  the  temperature  of  the 

312 


ILLUMINATING  GAS 


313 


checker-work  to  a  very  bright  red  heat.  From  the  top  of  the  super- 
heater, the  waste  gases  escape  into  a  hood  leading  into  the  open  air. 
When  both  the  carburettor  and  superheater  have  reached  the  desired 
temperature,  the  air  blasts  are  cut  off,  and  steam  is  introduced  into 


FIG.  97. 

the  generator,  where  it  is'  decomposed  by  the  incandescent  fuel, 
according  to  the  reactions.  The  water  gas  thus  formed  passes  into 
the  carburettor,  while  a  small  stream  of  oil  is  being  introduced  through 
a  pipe  at  the  top.  The  oil  is  decomposed  by  contact  with  the  hot 
checker-work,  forming  illuminating  gases  which  mix  with  the  water  gas, 
and  passing  into  the  superheater,  are  completely  fixed  as  non-condens- 
able gases. 

It  is  customary  to  run  the  air  blast  for  some  eight  minutes,  when 
the  fuel  reaches  a  temperature  of  about  1100°  C.  The  steam,  super- 
heated before  entering  the  generator,  is  run  about  six  minutes,  until 
the  temperature  of  the  generator  and  carburettor  has  fallen  below 
the  point  at  which  decomposition  occurs.  In  order  to  economize 
heat,  the  hot  carburetted  gas  is  passed  through  a  pipe  surrounded 
by  a  jacket,  within  which  the  oil  is  circulating,  thus  heating  it  be- 


314  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

fore  it  enters  the  carburettor.  The  lower  end  of  the  pipe  leading 
from  the  superheater  is  closed  by  a  water  seal,  to  prevent  any  back- 
ward rush  of  the  gas  during  the  operation  of  the  air  blast.  It  is  cus- 
tomary to  lead  the  gas  from  the  superheater  into  a  storage  holder, 
from  which  it  is  drawn  through  the  purifying  apparatus. 

In  this  process,  the  blowing  of  air  and  of  steam  are  intermittent, 
but  the  actual  formation  of  gas  is  accomplished  in  one  operation. 

The  second  method  of  preparing  illuminating  water  gas  is  the 
Wilkinson  process.  Water  gas  is  made  by  blowing  steam  into  the 
hot  coal  in  the  generator,  and  is  stored  in  the  holder.  A  measured 
quantity  of  gas  is  then  introduced  into  the  carburettor,  a  closed  iron 
box,  containing  slightly  inclined  plates,  over  which  the  exact  amount 
of  oil  necessary  to  carburet  the  gas,  is  flowing  in  very  thin  layers. 
The  carburettor  is  also  provided  with  a  steam  jacket  and  coils  to 
keep  the  temperature  high  enough  to  vaporize  the  oil.  These  vapors 
mix  with  the  gas  and  pass  at  once  into  the  fixing  apparatus,  which 
is  a  long,  narrow,  fire-clay  retort,  kept  at  a  white  heat  by  external 
fire.  Here  the  oil  vapors  are  "  cracked  "  into  hydrocarbons,  which 
are  non-condensable  gases,  and  being  mixed  with  water  gas,  render 
it  luminous  when  burned.  The  mixed  gases  then  go  directly  to  the 
scrubbers  and  purifiers.  For  1000  cubic  feet  of  gas,  about  50  pounds 
of  anthracite  and  4.2  to  5  gallons  of  naphtha  are  consumed. 

The  impurities  in  the  water  gas  are  essentially  the  same  as  those 
in  coal  gas,  and  the  method  of  washing  and  purifying  are  the  same. 

The  illuminating  value  of  coal  gas  is  frequently  raised  by  mixing 
it  with  carburetted  water  gas.  Owing  to  its  high  percentage  of  car- 
bon monoxide,  water  gas  is  exceedingly  poisonous  when  inhaled,  and 
much  care  is  necessary  to  prevent  leakage  into  inhabited  rooms  (see 
table,  p.  325). 

Coal  gas,  prepared  by  the  destructive  distillation  of  bituminous 
coal,  is  generally  made  by  the  smaller  gas  companies  in  this  country. 
In  Europe  scarcely  any  water  gas  is  made  for  illuminating  purposes. 
The  composition  and  yield  of  coal  gas  depend  upon  the  kind  of  coal 
used  and  the  manner  of  distillation.  A  "  fat  "  coal,  moderately  low 
in  sulphur,  and  caking  on  distillation  to  a  good  coke  (e.g.  the  Penn- 
sylvania gas  coals),  is  most  desirable  for  illuminating  gas.  The 
temperature  of  the  retort  is  a  very  important  factor  in  the  character 
of  the  distillation  products.  When  it  is  low,  the  quantity  of  gas 
formed  is  small,  but  it  contains  a  large  percentage  of  ilium inants, 
and  hence  is  of  a  high  candle  power.  When  the  temperature  in  the 


ILLUMINATING   GAS  315 

retort  is  high  the  effects  are  as  follows :  (a)  the  yield  of  gas  is 
much  increased,  but  the  percentage  of  methane,  ethane,  and  hydrogen 
is  much  greater,  and  since  these  have  very  little  illuminating  value, 
the  gas  is  of  low  candle  power;  (b)  the  yield  of  tar  is  increased; 
(c)  the  vapors  of  the  heavy  hydrocarbons  which  constitute  some  of  the 
tar  are  decomposed  on  coming  in  contact  with  the  hot  retort,  form- 
ing gases  of  lower  carbon  content,  and  depositing  free  carbon  on  its 
walls.  This  "  gas  carbon  "  *  adheres  very  firmly  and  if  allowed  to 
become  thick  causes  much  loss  of  heat.  It  is  especially  liable  to 
deposit  if  there  is  undue  pressure  in  the  retort,  which  may  be  the 
case  if  the  exhausters  are  not  working  properly ;  (d)  there  is  a  larger 
yield  of  organic  bodies  having  ring  nuclei  in  their  composition,  such 
as  naphthalene,  phenols,  anthracene,  etc.  These  not  only  cause  loss, 
but  also  cause  clogging  in  the  service  pipes  and  burners. 

The  products  of  the  distillation  are  gas,  ammoniacal  liquor,  tar, 
and  coke.  When  coal  is  distilled  for  coke  (p.  35),  the  ammoniacal 
liquor  and  tar  are  sometimes  saved  by  the  use  of  by-product  ovens, 
but  the  gases  are  burned  for  fuel  or  go  to  waste.  When  distilled  for 
illuminating  gas,  the  process  is  carried  on  with  a  view  to  the  best 
yield  of  high  quality  gas,  but  the  ammoniacal  liquor,  tar,  and  coke 
are  valuable  by-products.  The  coke  is  too  soft  for  metallurgical  pur- 
poses, and  is  chiefly  used  to  heat  the  retorts  or  sold  for  domestic  fuel. 

A  diagram  of  a  complete  plant  for  coal  gas  making  is  shown  in 
Fig.  98.  The  retorts  (A)  are  Q-shaped,  fire-clay  vessels,  about  8 
feet  long,  18  inches  wide,  and  15  inches  high;  they  are  set  six  or 
eight  together  in  a  furnace,  the  whole  constituting  what  is  called  a 
"  bench."  Each  retort  has  a  cast-iron  mouthpiece  projecting  out  of 
the  furnace,  and  carrying  the  door,  closed  by  a  screw  clamp.  Re- 
torts may  be  "  single,"  i.e.  closed  at  one  end  and  having  but  one 
door  for  charging  and  discharging ;  or  they  are  "  through  "  retorts, 
about  18  feet  long,  having  a  door  at  each  end,  so  that  they  may  be 
charged  or  emptied  from  either  side  of  the  furnace.  A  modified 
form  of  the  latter  is  the  "  inclined  "  retort,  set  at  an  incline  of  about 
32°,  the  coal  being  run  in  at  the  upper  end,  and  the  coke  discharged 
by  gravity,  by  opening  the  door  at  the  lower  end.  Vertical  retorts 
are  also  in  use.  Each  bench  is  heated  to  1000°  or  1200°  C.  by  a  coke 
fire  on  a  grate  below  the  retorts,  or,  in  more  modern  plants,  by  gen- 
erator gas.  A  number  of  benches  are  built  together,  and  constitute  a 
"  stack." 

*  Gas  carbon  is  used  for  electric  light  carbons,  battery  plates,  and  other  electri- 
cal appliances.  It  is  denser  and  purer  than  most  other  forms  of  carbon. 


316 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


FIG.  98. 

From  the  front  of  each  retort  a  vertical  cast-iron  pipe  (B)  about 
6  inches  in  diameter,  and  called  the  "  stand-pipe,"  ascends  to  the 
top  of  the  bench,  where  it  joins  the  "  bridge-"  and  "  dip-pipes," 
which  conduct  the  volatile  products  from  the  retort  to  the  hydraulic 
main  (C).  This  is  a  long  covered  trough,  extending  the  entire  length 
of  the  stack,  and  receiving  the  gas  .and  distillate  from  each  retort. 
In  it  the  greater  part  of  the  tar  and  oily  products  condense  and  collect 
under  the  water  which  is  kept  in  the  main  to  act  as  a  seal  to  the  ends 
of  the  dip-pipes,  to  prevent  the  gas  from  passing  back  into  the  retort 
when  the  latter  is  opened.  Ammonium  salts,  such  as  sulphate,  sul- 
phide, and  carbonate,  are  washed  from  the  gas  as  it  bubbles  through 
the  water,  and  are  afterwards  recovered  (p.  151).  The  ends  of  the 
dip-pipes  must  not  extend  more  than  2  inches  into  the  water ;  other- 
wise, there  is  pressure  in  the  retort  and  consequent  loss  from  leakage 
and  from  deposition  of  carbon  in  the  retort  and  stand-pipe.  If  the 
gas  is  allowed  to  cool  in  contact  with  the  tar,  the  latter  absorbs  some 
of  the  illuminants,  thus  reducing  the  candle  power  (p.  323).  If  the 
stand-pipes  are  too  hot,  the  volatile  constituents  of  the  tar  are  driven 
out,  and  a  very  thick  mass  deposits,  causing  clogging. 

From  the  hydraulic  main  a  pipe  (not  shown)  leads  to  the  con- 
denser (D),  which  consists  of  a  series  of  vertical  cast-iron  pipes,  con- 
nected by  bends  at  the  top,  and  opening  at  the  bottom  into  an  iron  box. 


ILLUMINATING   GAS  317 

This  box  is  divided  by  transverse  partitions  which  do  not  extend  to 
the  bottom,  merely  dipping  into  the  ammoniacal  liquor  and  tar  con- 
tained in  it.  The  liquor  forms  a  seal,  thus  forcing  the  gas  to  pass 
through  the  pipes,  while  the  condensed  products  flow  along  the  bottom 
of  the  box  to  the  tar  well.  These  condensers  are  simply  air  cooled, 
but  certain  forms  are  constructed  with  water  coolers.  In  those  most 
frequently  in  use  in  this  country  the  pipes  are  laid  at  a  slight  incline 
to  the  horizontal. 

The  annular  condenser  consists  of  a  series  of  vertical  pipes  con- 
nected by  diagonal  pipes  leading  from  the  bottom  of  one  to  the  top 
of  the  next.  Through  each  of  these  vertical  pipes  a  smaller  tube 
passes  parallel  to  the  length  of  the  pipe  and  opening  to  the  air  at 
both  ends,  thus  forming  an  annular  space  in  each  pipe,  through 
which  the  gas  passes  downward,  and  then  through  the  diagonal  pipe 
to  the  top  of  the  next.  In  this  way  a  very  large  air-cooled  surface 
is  obtained.  At  the  bottom  of  each  cooling  pipe  a  small  pipe  car- 
ries away  the  condensed  tar  and  liquor. 

The  tubular  condenser  consists  of  a  rectangular  box  about  2  feet 
wide  and  20  feet  high,  divided  into  narrow  sections  by  partitions 
extending  alternately  to  within  a  few  inches  of  the  top  and  of  the 
bottom.  Through  each  section,  a  number  of  narrow  horizontal  tubes, 
open  to  the  air  at  each  end,  extend  from  one  side  of  the  box  to  the 
other.  In  this  way  the  gas  passing  through  the  sections  is  exposed 
to  a  very  large  cooling  surface. 

Water  condensers  consist  essentially  of  pipes  surrounded  by  flow- 
ing water.  Through  these  the  gas  is  made  to  pass  in  a  direction 
opposite  to  that  in  which  the  Water  flows.  By  regulating  the  supply 
of  water,  the  temperature  is  easily  controlled. 

The  object  of  the  condenser  is  to  cool  the  gas  slowly  to  the  tem- 
perature of  the  atmosphere,  provided  this  in  not  under  50°  C.  Cool- 
ing below  this  causes  condensation  of  some  of  the  illuminants,  with 
corresponding  loss.  If  the  cooling  is  very  rapid,  the  tarry  matter 
separates  quickly,  and  drags  some  of  the  lighter  hydrocarbons  down 
with  it. 

The  exhauster  (E,  Fig.  98)  draws  the  gas  from  the  retort,  through 
the  hydraulic  main  and  condenser,  and  acts  as  a  pump  forcing  it 
through  the  remaining  parts  of  the  plant.  By  drawing  the  gas  out 
of  the  retort  quickly  there  is  less  decomposition  of  the  gas  itself, 
and  hence  less  carbon  is  deposited  in  the  retort;  a  larger  yield 
results  and  less  fuel  is  necessary,  while  the  retort  lasts  longer. 

Another  form  of  exhauster  is  a  direct-acting  pump,  which  draws 


318  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

the   gas    from    the    retort    and    condenser,    and    forces    it    to    the 
purifiers. 

Root's  rotary  exhauster  is  frequently  employed,  as  is  also  Beal's 
(Fig.  99).  This  consists  of  an  outer  circular  casing  having  inlet  and 
outlet  pipes,  and  an  inner  revolving  drum  (B),  turning  on  an  eccentric 
axis  in  such  a  way  that  the  drum  just  touches  the  lowest  point  of  the 
inner  surface  of  the  casing.  Through  slots  cut  in  the  drum,  two 
blades  or  diaphragms  (D)  slide  freely  over  one  another,  to  form  a 
double  diaphragm,  variable  in  width,  according  to  the  relative  posi- 
tion of  the  blades  to  each  other.  In  the  outer  end  of  each  blade  is  a 


FIG.  99.  FIG.  100. 

pin,  which  travels  in  a  circular  groove  sunk  in  the  ends  of  the  casing. 
Thus  as  the  drum  revolves  about  its  axis,  the  pins,  travelling  in  the 
fixed  groove,  draw  the  blades  in  and  out,  across  the  axis  of  the  drum. 
The  outer  ends  of  the  blades  are  thus  always  kept  in  contact  with  the 
walls  of  the  casing.  The  exhauster  is  driven  by  an  engine,  and  the 
rotary  blades  and  drum  catch  the  gas  which  enters  through  the  inlet, 
and  force  it  out  through  the  other  pipe. 

The  steam  jet  exhauster  (Fig.  100  *)  is  effective,  but  heats  the 
gas,  which  is  afterwards  cooled  in  the  washer.  A  jet  of  steam  is 
blown  through  conical  openings  into  a  wide  pipe,  drawing  the  gas 
along  with  it  into  the  cones. 

The  tar  extractor  (F,  Fig.  98)  is  a  short  tower  filled  with  numer- 
ous horizontal  perforated  plates.  The  friction  of  the  gas  in  passing 
through  the  small  holes  in  these  plates  removes  the  last  traces  of  tar  and 
prevents  clogging  in  the  scrubber.  In  Europe  the  apparatus  of  Pelouze 
and  Audouin  is  much  employed.  This  is  a  bell  made  up  of  three  layers 
of  wire  netting,  or  of  perforated  plates,  which  is  suspended  in  a  water 
seal.  The  gas  enters  under  the  bell  and  passes  through  the  meshes 

*  After  Ost,  Lehrbuch  d.  tech.  Chemie. 


ILLUMINATING  GAS  319 

or  perforations  of  the  bell  walls,  to  which  the  tar  particles  attach 
themselves  and  finally  drop  to  the  bottom  and  run  off  by  a  special 
pipe. 

The  scrubber  and  washer  are  intended  to  remove  the  ammonia 
and  part  of  the  carbon  dioxide  and  hydrogen  sulphide.  In  the 
former  the  gas  is  brought  into  contact  with  thin  films  or  layers  of 
ammoniacal  liquor  from  the  hydraulic  main  or  condensers,  which 
trickles  over  coke,  twigs,  wooden  slats,  or  pebbles,  in  a  tower.  This 
liquor  absorbs  some  of  the  carbon  dioxide  and  hydrogen  sulphide, 
which  combine  with  the  ammonia.  In  the  washer  the  gas  is  brought 
in  contact  with  pure  water,  trickling  over  twigs,  coke,  etc.,  and 
which  removes  the  ammonia  from  the  gas. 

Tower  scrubbers  are  tall  cast-iron  vessels  built  in  segments,  each 
of  which  has  a  "  grid  "  or  grating,  upon  which  the  filling  material 
is  supported.  Two  towers  are  always  used  in  conjunction,  the  first 
fed  with  ammoniacal  liquor  and  the  second  with  water.  The  amount 
of  liquor  and  water  is  carefully  regulated,  and  the  gas  entering  at 
the  bottom  of  the  first  tower  passes  up  and  then  to  the  bottom  of 
the  second,  and  is  thus  first  brought  into  contact  with  the  strongest 
liquor  and  finally  with  pure  water.  These  tower  scrubbers  are  now 
only  used  in  old  plants ;  in  all  modern  establishments  they  have  been 
replaced  by  scrubber-washer  machines. 

The  Standard  scrubber-washer  machine  (G,  Fig.  98)  is  a  Q-shaped 
iron  vessel  divided  into  a  series  of  narrow  chambers  by  transverse 
partitions.  In  the  upper  half  of  the  apparatus  is  a  revolving  shaft 
carrying  a  number  of  thin  wooden  grids,  bolted  together  in  parallel 
segments,  with  blocks  making  a  space  of  about  one-eighth  of  an  inch 
between  each  pair  of  grids.  A  group  of  these  slats  revolve  in  each 
chamber.  Water  at  about  60°  F.  is  admitted  to  the  last  chamber  of 
the  series,  at  the  rate  of  about  one  gallon  for  each  1000  cubic  feet  of 
gas,  and,  automatically  regulated,  flows  from  chamber  to  chamber  in 
a  direction  opposite  to  that  in  which  the  gas  is  passed.  Thus  the 
fresh  water  comes  in  contact  with  the  most  nearly  purified  gas.  The 
level  of  the  water  is  lower  in  each  succeeding  chamber,  until  in  the 
first  chamber,  where  the  gas  enters  the  apparatus,  the  strong  ammo- 
niacal liquor  is  only  a  few  inches  deep. 

By  the  revolution  of  the  shaft,  the  grids  are  submerged  in  the 
liquor,  and  freshly  wetted  surfaces  are  brought  into  the  urjper  part 
of  the  apparatus.  By  a  suitable  arrangement  of  baffle  plates,  the 
gas  is  made  to  enter  each  chamber  at  the  centre,  and  find  its  way  to 
the  circumference  by  passing  through  the  narrow  spaces  between  the 


320  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

grids.  The  water,  forming  a  thin  film  on  them,  absorbs  the  ammonia, 
carbon  dioxide,  etc. ;  and  as  the  shaft  revolves  from  12  to  15  times 
per  minute,  the  solution  formed  is  at  once  mixed  with  the  liquor  in 
the  bottom  of  the  chamber.  The  machine  works  effectively,  and  in 
this  country  is  rapidly  replacing  the  tower  scrubbers. 

From  the  scrubbers  the  gas  passes  to  the  purifiers  (H,  Fig.  98), 
whose  chief  purpose  is  to  remove  sulphur  compounds.  They  are 
shallow  rectangular  iron  boxes,  each  having  a  false  bottom,  upon 
which  the  purifying  material  rests.  The  gas  enters  under  this  grating 
and  leaves  by  a  pipe  opening  just  under  the  cover,  which  rests  in  a 
hydraulic  seal,  and  is  lifted  by  a  travelling  crane.  Usually  four  puri- 
fiers are  placed  in  a  series,  one  of  which  is  emptied  and  recharged  at 
a  time,  without  interrupting  the  purification  process.  The  foul  gas 
enters  the  most  nearly  exhausted  purifier,  and,  passing  through  the 
others,  leaves  the  apparatus  through  that  most  recently  charged,  con- 
nection being  made  between  the  purifiers  by  means  of  a  complicated 
piece  of  apparatus  (L  and  0,  Fig.  98)  called  the  centre  seal. 

The  purifying  materials  may  be  slaked  lime  or  hydrated  ferric 
oxide.  Lime  is  the  oldest  material  used  and  is  also  the  best,  since 
it  removes  both  the  carbon  dioxide  and  carbon  disulphide.  But  it  is 
expensive,  and  the  spent  lime,  having  a  most  offensive  odor  and  con- 
siderable bulk,  is  difficult  to  dispose  of.  The  lime  should  be  thor- 
oughly slaked  several  days  before  use,  and  should  contain  as  much 
water  as  it  will  hold  without  becoming  pasty  or  liquid.  It  is  placed 
in  the  purifiers  in  layers  about  six  inches  deep.  The  reactions  occur- 
ring with  lime  are :  — 

1)  Ca(OH)2  +  2  H2S  =  Ca(SH)2  +  2  H2O. 

2)  Ca(OH)2  +  H2S  =  CaS  +  2  H2O. 

3)  CaS  +  CSa  =  CaCS3  (calcium  thiocarbonate). 

4)  Ca(OH)2  +  CO2  =  CaCO3  +  H2O. 

Since  carbon  dioxide  will  decompose  calcium  sulphide,  sul- 
phydrate,  or  thiocarbonate,  if  gas  containing  it  is  passed  through  a 
foul  purifier,  the  following  is  liable  to  take  place :  - 

CaS  +  CO2  +  H2O  =  CaCO3  +  H2S. 
.     CaCSs  +  CO2  +  H2O  =  CaCO3  +  €82  +  H2S. 

The  volatile  sulphides  thus  liberated  must  be  removed  in  a  second 
purifier,  into  which  no  carbon  dioxide  enters.  Carbon  dioxide  has  a 
deleterious  effect  on  the  illuminating  power  of  the  gas. 


ILLUMINATING  GAS  321 

When  iron  oxide  is  used,  only  the  hydrogen  sulphide  is  removed 
from  the  gas  :  — 

1)  Fe2O3  •  3  H2O  -t  3  H2S  =  2  FeS  +  S  +  6  H2O. 

2)  Fe2O3  •  3  H2O  +  3  H2S  =  Fe2S3  +  6  H2O. 

The  oxide  is  a  natural  bog  iron  ore,  Fe2O3  •  3  H2O.  When  fresh, 
it  contains  about  50  per  cent  water  and  a  large  amount  of  vegetable 
matter,  but  before  use  it  is  dried  until  about  one-half  of  the  moisture 
is  expelled,  and  is  then  mixed  with  an  equal  bulk  of  sawdust  to  ren- 
der it  more  porous.  When  it  becomes  inactive  through  absorption  of 
sulphur,  it  is  "  revivified  "  by  removing  it  from  the  purifier  and 
spreading  it  in  a  layer  a  foot  or  more  in  depth,  where  the  air  can 
act  upon  it.  Considerable  heat  is  evolved  by  the  action  of  the  oxy- 
gen of  the  air  on  the  iron  sulphides :  — 

2  FeS  +  3  O  =  Fe2O3  +  2  S. 
Fe2S3  +  3  O  =  Fe2O3  +  3  S. 

Thus  free  sulphur  is  deposited  in  the  oxide.  The  ore  may  be  revivi- 
fied repeatedly  until  the  free  sulphur  accumulates  in  it  to  the  amount 
of  50  or  55  per  cent,  when  the  proper  action  in  the  purifiers  is  hin- 
dered, and  fresh  oxide  must  be  used.  If  some  air  is  admitted  along 
with  the  gas,  the  iron  oxide  is  revivified  in  the  purifiers,  and  need 
not  be  removed  so  often ;  but  this  dilutes  the  gas  slightly  with  nitro- 
gen. One  ton  of  good  iron  oxide  will  purify  ten  to  twelve  million  cubic 
feet  of  gas.  Sometimes  lime  is  used  before  the  iron  oxide,  in  order 
to  remove  carbon  dioxide.  Any  sulphur  compounds  of  the  lime 
which  may  be  formed  are  decomposed  by  the  carbon  dioxide  in  the 
foul  gas  (see  above).  Considerable  carbon  dioxide  is  present  in 
unpurified  water  gas,  and  is  generally  thus  removed  before  the  gas 
enters  the  iron  oxide  purifiers. 

The  purified  gas  passes  through  the  station  meter  (I,  Fig.  98)  and 
then  to  the  holder  (J),  from  which  it  is  delivered  to  the  street  mains. 

The  Feld  process  of  gas  purification  has  found  some  favor  in 
Europe.  The  gas,  which  has  not  been  freed  of  ammonia,  is  washed  in 
a  scrubber  with  a  dilute  solution  of  ferrous  sulphate ;  both  ammonia 
and  hydrogen  sulphide  are  absorbed :  - 

FeSO4  4-  2  NH3  +  H2S  =  FeS  +  (NH4)2SO4. 

The  exhausted  wash-liquor  is  regenerated  by  blowing  sulphur  dioxide 
gas  into  it,  forming  soluble  ferrous  thiosulphate  and  precipitating  sul- 
phur :  -  2  FeS  +  3  SO2  =  2  FeSsOg  +  S. 


322  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

This  liquid,  with  the  sulphur  in  suspension,  is  used  in  the  scrubber 
for  more  crude  gas  :  — 

+  2  NH3  +  H2S  =  FeS  + 


This  liquor  is  in  turn  regenerated  by  blowing  a  mixture  of  air  and 
sulphur  dioxide  into  it,  when  the  thiosulphate  is  oxidized  to  sul- 
phate :  — 

2  FeS  +  2(NH4)2S2O3  +  3  SOa  +  2  O2  =  2'FeSO4  +  2(NH4)2SO4+5  S. 


This  is  repeated  until  the  ammonium  sulphate  reaches  30  to  40  per 
cent,  when  the  sulphur  is  filtered  off  ;  the  iron  precipitated  as  ferrous 
sulphide  is  also  filtered  and  the  sludge  returned  to  the  process.  The 
ammonium  sulphate  is  recovered  by  evaporation. 

Cyanides  (p.  289)  are  recovered  from  the  impure  gas  in  some  of 
the  large  works.  When  this  is  done  by  the  use  of  iron  salts,*  with- 
out previous  removal  of  the  ammonia,  a  special  arrangement  of  the 
apparatus  is  desirable.  The  tar  extractor  is  put  behind  the  air- 
cooled  condenser;  next  is  a  standard  scrubber,  charged  with  heavy 
tar  oils  in  the  forward  compartments  to  remove  naphthalene,  and  the 
iron  solution  is  in  the  later  compartments  to  remove  the  cyanogen; 
following  this  is  the  water-cooled  condenser,  and  then  the  ammonia 
scrubber.  Thus  the  gas  enters  the  ammonia  scrubber  nearly  cold. 
This  removal  of  cyanogen  from  the  gas  renders  the  activity  of  the 
iron  oxide  in  the  purifiers  of  greater  duration,  for  only  the  hydrogen 
sulphide  is  to  be  removed,  no  sulphocyanide  nor  Prussian  blue  is 
formed,  and  the  ultimate  amount  of  sulphur  in  the  mass  readily  reaches 
50  per  cent,  when  the  material  is  suitable  for  making  sulphuric  acid. 

The  ammoniacal  liquors  from  the  hydraulic  main,  condensers, 
and  scrubbers  are  mixed,  forming  "  gas  liquor  "  of  approximately 
"  10  ounce  "  strength,  i.e.  the  ammonia  gas  which  can  be  liberated 
from  one  gallon  of  the  liquor  will  neutralize  10  ounces  by  weight  of  real 
sulphuric  acid.  It  is  used  for  the  production  of  ammonia  (p.  151). 
The  tar  from  the  tar  well  is  shipped  to  the  tar  distiller  (p.  327). 

The  usual  impurities  found  in  gas  are  ammonia,  hydrogen  sul- 
phide, and  carbon  dioxide.  Ammonia  is  detected  by  holding  a  strip 
of  wet  turmeric  or  litmus  paper  in  a  stream  of  the  gas  ;  the  former 
becomes  brown  or  red,  and  the  latter  blue.  For  hydrogen  sul- 
phide, paper  wet  in  lead  acetate  or  silver  nitrate  is  used.  Carbon 
dioxide  is  detected  by  shaking  a  small  bottle  of  the  gas,  freed  from 
hydrogen  sulphide,  with  lime  or  baryta  water. 

*  Journal  fur  Gasbeleuchtung,  1899,  470. 


ILLUMINATING  GAS  323 

The  yield  from  one  ton  of  good  gas  coal  is  approximately  :  — 

.10,000  cu.  ft.  16  candle  power  gas. 
1400  pounds  coke. 
120  pounds  tar. 
20  gallons  ammoniacal  liquor  (10  to  12  oz.). 

The  illuminating  power  of  gas  is  expressed  in  "candles,"  by 
which  is  meant  the  ratio  of  its  illuminating  power  to  that  of  a  "  stand- 
ard candle,"  as  measured  by  a  photometer.  The  English  standard 
is  the  light  of  a  sperm  candle,  weighing  one-sixth  of  a  pound,  when 
burning  120  grains  per  hour.  But  this  is  subject  to  variation,  and 
much  ingenuity  has  been  expended  in  devising  a  better  standard.  A 
burner  designed  for  use  with  a  mixture  of  air  and  pentane,  C5Hi2,  has 
found  some  favor  in  Europe.  In  Germany  the  light  of  a  lamp  burning 
amyl  acetate,  with  a  specified  height  of  flame  and  size  of  wick,  is  the 
official  standard.  In  this  country  standard  candles  are  used.  When 
testing  gas,  it  is  customary  to  burn  it  at  the  rate  of  5  cu.  ft.  per  hour, 
in  a  burner  of  the  argand  type.  Ordinary  coal  gas  is  about  16  candle 
power,  but  it  is  sometimes  "  enriched  "  by  putting  into  the  retort, 
along  with  each  charge  of  coal,  an  iron  cylinder  containing  petroleum 
oil.  This  is  closed  with  a  cork,  which  burns  out,  and  the  escaping  oil 
is  decomposed,  the  vapors  mixing  with  the  coal  gas,  increasing  its  illu- 
minating power. 

Another  method  of  enriching  coal  gas  is  the  addition  of  benzol 
vapors,  the  gas  having  been  previously  scrubbed  with  heavy  oil  to 
remove  naphthalene,  phenols,  and  other  constituents. 

A  modern  improvement  in  gas  lighting  is  the  introduction  of  in- 
candescent burners,  in  which  the  non-luminous  flame  of  a  Bunsen 
burner  is  made  to  heat  a  mantle  or  gauze  composed  of  the  oxides  of 
various  rare  earths,  especially  thorium  and  cerium,  which  possess  in 
high  degree  the  property  of  selectively  radiating  light  at  relatively 
low  temperatures.  The  mantle  heated  to  incandescence  glows  with 
a  powerful  light,  while  very  little  heat  is  given  out.  These  burners 
consume  about  three  and  one-half  feet  of  gas  per  hour,  and  their 
efficiency  is  four  times  that  of  an  ordinary  argand  burner.  They  are 
advantageous  to  use  with  a  gas  of  low  illuminating  power,  provided  it 
has  considerable  heating  value. 

Oil  gas  is  now  largely  made  by  "  cracking  "  certain  petroleum,  tar, 
or  shale  oils  in  retorts.  In  Pintsch's  process  the  retort  is  divided 
by  a  partition  into  an  upper  and  lower  chamber ;  the  oil  is  cracked 
in  the  upper  compartment,  and  the  vapors  pass  into  the  lower  one, 


324  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

which  is  heated  to  about  1000°  C.,  where  they  are  "  fixed  "  and  form 
permanent  gases.  In  Peebles'  process  the  retorts  are  not  so  hot, 
and  the  oil  is  partly  cracked  and  partly  distilled ;  the  heavier  fractions 
condense  and  return  to  the  retort,  and  only  very  volatile  hydrocarbons 
leave  the  apparatus.  Purified  oil  gas  has  a  high  candle  power,  usually 
over  50,  and  is  burned  in  special  forms  of  burner,  otherwise  it  is  liable 
to  smoke  or  deposit  soot ;  it  is  rich  in  benzene  and  olefine  hydrocarbons, 
and  may  be  burned  alone  or  used  to  enrich  other  gases.  Burning 
with  pure  oxygen  improves  its  combustion  and  illuminating  power 
greatly.  Pintsch  gas  is  much  used  for  lighting  railroad  cars;  it  is 
compressed  into  cylinders  for  carriage,  but  the  pressure  must  be  low 
or  great  loss  of  illuminating  power  occurs  owing  to  the  condensation 
of  the  heavy  illuminants. 

Blau  gas  *  is  made  by  "  cracking  "  petroleum  in  a  steel  retort,  at 
low  red  heat  (500°-600°  C.) ;  both  liquid  and  gaseous  products  re- 
sult, which  are  cooled  to  condense  the  higher  boiling  constituents.  The 
gas  then  passes  a  purifier  (iron  oxide  and  lime)  to  remove  hydrogen 
sulphide  and  carbon  dioxide ;  then  it  is  compressed  in  a  four-stage 
compressor  to  100  atmospheres,  whereby  part  of  it  liquefies,  and  under 
the  heavy  pressure,  the  liquid  hydrocarbons  dissolve  much  of  the  fixed 
gases  and  hold  them  in  solution.  The  liquid  is  then  charged  into  steel 
cylinders  for  use.  The  residual  unabsorbed  gas  separated  from  the 
liquid  is  used  in  gas  engines  driving  the  compressors. 

Blau  gas  is  nearly  free  from  carbon  monoxide  and  consists  essen- 
tially of  methane  and  hydrogen  dissolved  in  saturated  and  unsaturated 
hydrocarbons,  which  impart  high  calorific  and  illuminating  value  (50 
c.  p.).  It  is  used  in  isolated  buildings,  factories,  yachts,,  and  railway 
cars ;  and  with  oxygen  for  autogenous  welding  and  metal  cutting. 

Acetylene  is  made  from  calcium  carbide  (p.  266)  by  treating  with 

CaC2  +  2  H2O  =  Ca(OH)2  +  C2H2. 

One  ton  of  80  per  cent  carbide  yields  about  9000  cu.  ft.  of  acetylene 
gas.  The  crude  gas  is  usually  contaminated  with  hydrogen  sulphide, 
phosphine,  and  ammonia ;  it  is  purified  by  passing  over  bleaching  pow- 
der, chromic  acid,  or  cuprous  chloride.  When  burned  under  pressure, 
in  a  special  form  of  burner,  it  yields  a  very  brilliant  light.  It  is  not 
used  to  enrich  coal-  or  water-gas,  since  its  candle  power  is  much  lowered 
by  mixing  with  other  gases.  With  air  in  greatly  varying  proportions 
the  gas  forms  explosive  mixtures. 

Heavily  compressed  acetylene  gas  is  liable   to  explode;    hence 

*  Jour.  Soc.  Chem.  Ind.,  1908,  550.    Met.  and  Chem.  Eng.,  1914,  153. 


ILLUMINATING  GAS 


325 


storage  in  the  compressed  state  in  gas  tanks  is  dangerous.  But  enor- 
mous quantities  of  the  gas  dissolve  in  acetone  under  pressure,  and  the 
solution  is  not  explosive ;  on  releasing  the  pressure,  the  gas  is  evolved 
rapidly  and  steadily.  By  filling  the  cylinders  completely  full  of  some 
porous  material,  as  asbestos,  or  charcoal  embedded  in  cement,  after 
thorough  drying,  a  considerable  quantity  of  the  acetone-acetylene 
solution  can  be  introduced  at  about  15  atmospheres  pressure  and  safely 
stored  or  transported.  Cylinders  of  the  acetylene  solution  are  much 
used  for  automobile  and  car  lighting.  Acetylene  is  considerably 
used  for  illuminating  detached  country  houses  and  factories,  and  for 
the  public  supply  of  towns. 

When  burned  with  oxygen,  acetylene  yields  an  intensely  hot 
flame  (2500°  C.)  Oxy-acetylene  blow  pipes  are  much  used  for  autoge- 
nous welding  of  iron,  steel,  and  other  metals ;  also  for  cutting  and 
boring  steel  plates  and  beams,  the  metal  being  rapidly  melted  in  a 
very  narrow  area  at  the  point  of  the  flame  jet. 

Air  gas,  so-called,  is  made  by  blowing  a  carefully  regulated  current 
of  air  through  layers  of  the  very  volatile  petroleum  distillates,  of  from 
80  to  90°  Be.  The  air,  carrying  sufficient  vapor  to  form  a  combustible 
mixture,  goes  directly  into  the  burner,  since  it  cannot  be  piped  very 
far  without  condensation  of  the  illuminants.  Air  gas  is  much  used 
where  other  gas  is  not  available. 

In  some  parts  of  Europe,  where  coal  is  expensive,  gas  is  made  by 
distilling  dried  peat.  The  gas  contains  more  carbon  dioxide  than 
coal  gas,  and  more  lime  is  needed  for  purification ;  it  is  about  18 
candle  power,  and  considerable  tar  and  ammoniacal  liquor  are  obtained. 
The  composition  of  typical  kinds  of  gas  is  shown  in  the  following 
table.* 

ANALYSES 


COAL 

WATEB 
(CARBURETTED) 

WATER 

(F0EL) 

OIL 

Candle  power       ..    . 
Illuminants      .... 
Marsh  gas       .... 
Hydrogen        .... 

17.5 
5.0 
34.5 
49.0 

25.0 
16.6 
19.8 
32.1 

1.0 
52.0 

65.0 
45.0 

38.8 
14.6  Ethane 

Carbonic  oxide    . 
Nitrogen     ... 

7.2 
32 

26.1 
2.4 

38.0 
3.0 

1  i 

Oxygen       .     .     .-  .r-'  ;. 
Carbonic  acid 

1.1 

3.0 

6.0 

*  C.  D.  Jenkins.     Reports  of  the  Mass.  State  Gas  Inspector. 


326  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

The  gas  produced  in  by-product  coke  ovens  contains  some  benzene 
(C6H6),  and  if  the  gas  is  not  to  be  used  for  illuminating  purposes,  this 
benzene  may  be  washed  out  of  the  gas  in  counter-current  scrubbers 
using  mineral  oil.  The  oil  is  then  distilled  with  steam  to  recover  the 
benzene,  and  the  residual  oil  returned  to  the  scrubber.  Coal-gas 
intended  to  be  used  for  illuminating  may  be  scrubbed  in  the  same 
way,  but  in  this  case  other  illuminants  must  later  be  added  to  the 
gas. 

REFERENCES 

Practical  Treatise  on  the  Manufacture  and  Distribution  of  Coal  Gai 

Samuel  Clegg,  London,  1859. 
Traite  theoretique  et  pratique  de  la  Fabrication  du  Gaz.     E.  Borias,  Paris 

1890. 

Manufacture  of  Gas  from  Tar,  Oil,  etc.     W.  Burns,  New  York,  1887. 
Fabrikation  der  Leuchtgase.     G.  Thenius,  Leipzig,  1891. 
The  Chemistry  of  Illuminating  Gas.     N.  H.  Humphreys,  London,  1891 
Handbuch  fur  Gas-Beleuchtung.     E.  Schilling,  1892. 
A  Treatise  on  Gas  Manufacture.     W.  King.     (King.) 
Gas  Engineer's  Handbook.     T.  Newbiggin,  London,  1898.     (King.) 
Acetylen  in  der  Technik.     F.  B.  Ahrens,  1899. 
Acetylene.     V.  B.  Lewes,  1900. 
A  Textbook  of  Gas  Manufacture.     John  Hornby,  London,  1902.     (Bell 

and  Sons.) 

Acetylene.     F.    H.    Leeds   and   W.    J.    A.    Butterfield.     London,    1903. 
The  Chemistry  of    Gas  Manufacture.     W.   J.   A.   Butterfield,   3d   ed., 

London,  1904. 

Chemistry  of  Gas  Manufacture.     H.  M.  Royle,  1907. 
Handbook  of  American  Gas  Engineering  Practice.     M.  N.  Latta,  1907. 
Modern  Appliances  in  Gas  Manufacture.     F.  W.  Stevenson. 
Practical  Testing  of  Gas  and  Gas  Meters.     C.  H.  Stone,  1909. 
Gasbeleuchtung  und  Gasindustrie.     H.  Strache,  Braunschweig,  1913. 
Journal  of  Gas  Lighting.     London.     Vols.  69,  60,  61,  62,  and  others. 

(Coal  Gas.) 


COAL-TAR 

The  tar  from  the  hydraulic  main  and  condensers  of  the  gas  works 
is  a  black,  oily,  foul-smelling  liquid  averaging  1.15  sp.  gr.  Its  com- 
position is  very  complex,  and  it  is  mixed  with  some  of  the  gas  liquor, 
retains  in  solution  some  constituents  of  the  gas,  and  carries  fine  carbon 
in  suspension.  In  the  early  days  of  gas  making,  no  use  being  known 
for  tar,  it  became  a  great  nuisance.  But  the  discovery  of  important 
derivatives  from  it  has  given  rise  to  great  industries. 

Coal-tar  is  used  to  some  extent  without  treatment  for  preserving 
timber,  as  a  protective  paint  and  cement  in  chemical  works ;  in  form- 
ing certain  furnace  linings ;  and  as  liquid  fuel.  But  much  of  the  tar 
produced  is  fractionally  distilled  to  separate  the  more  important  con- 
stituents. These  consist  of :  (a)  the  hydrocarbons,  the  most  valuable, 
bodies  of  a  neutral  character  not  affected  by  dilute  acids  nor  alkali ; 
(6)  the  phenols,  bodies  of  a  weak  acid  character,  and  containing 
oxygen ;  (c)  the  bases,  containing  nitrogen,  and  often  present  in  such 
small  amounts  that  they  are  not  recovered.  The  method  of  distilla- 
tion varies  much  as  the  market  for  the  distillates  fluctuates,  and  the 
composition  of  the  tar  from  different  gas  works  is  variable.  If  ben- 
zenes are  low  in  price,  the  light  oils  are  collected  together.  Often  the 
phenols  are  not  separated,  when  the  demand  for  them  is  not  great. 
Some  tars  are  distilled  only  until  the  light  oils  are  removed,  and  the 
residue  variously  employed.  But  if  anthracene  is  present,  the  heavy 
oils  are  distilled  off,  and  the  residue  forms  pitch. 

When  received  from  the  gas  works,  the  tar  is  run  into  a  tank,  or 
cistern,  and  allowed  to  stand  until  the  ammoniacal  liquor  mixed  with 
it  separates  by  gravity.  To  facilitate  this  the  tar  may  be  warmed  by  a 
steam  coil  in  the  tank,  especially  in  cold  weather.  Gas  liquor  causes 
frothing  in  the  still,  so  is  removed  as  completely  as  possible,  and  sent 
to  the  ammonia  distiller. 

Formerly,  old  boilers  often  served  as  stills,  but  in  modern  works 
the  stills  are  constructed  for  the  purpose. 

In  America  tar  distillation  is  conducted  in  a  rougher  and  less  per- 
fect manner  than  in  Europe.  Horizontal  stills  of  from  15  to  25  tons 
capacity,  similar  in  construction  to  petroleum  stills  (p.  339)  but  smaller, 
are  commonly  used.  The  condenser  worm  is  ordinarily  wrought  iron, 
electrically  welded  to  avoid  joints  as  far  as  possible.  Perforated 
pipes  within  the  still  permit  the  use  of  steam  or  compressed  air,  tc 

327 


328  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

assist  in  distilling  the  heavy  oils  and  prevent  adhesion  of  coke  to 
the  plates. 

In  Europe  vertical  cylinders  of  wrought  iron  or  steel  plates  from 
three-eighths  to  one-half  inch  thick  are  preferred;  the  diameter 
is  equal  to  the  height ;  the  bottom  is  concave,  and  the  top  is  a  cast- 
iron  dome,  having  a  manhole,  an  inlet  pipe  for  the  tar,  a  broad,  curved 
vapor  pipe  ("  goose-neck  "),  and  a  small  overflow  pipe  ("  tell-tale  ") ; 
also  a  thermometer  tube  and  a  safety-valve  usually ;  if  the  latter  is 
omitted,  the  manhole  cover  is  not  screwed  down,  but  closes  the  open- 
ing by  its  own  weight;  should  excessive  pressure  develop  within 
the  still,  the  cover  is  lifted  and  the  vapors  escape.  The  arched  bottom 
rises  to  a  considerable  height,  thus  distributing  the  heat  into  the 
interior  of  the  mass  of  tar,  and  the  outlet  pipe  being  placed  at  the  lowest 
point,  it  is  also  of  assistance  in  emptying  the  still.  The  bottom  is 
sometimes  protected  from  direct  contact  with  the  flame  by  a  brick 
arch  (curtain  arch).  There  is  usually  a  coil  in  the  still,  through  which 
superheated  steam  is  blown,  towards  the  end  of  the  process,  to  assist 
in  the  distillation  of  the  heavy  oils. 

These  upright  stills  are  set  in  furnaces  so  that  the  flames  play 
under  the  bottoms,  and  about  half-way  up  the  height,  through  side 
flues  in  the  brick  setting.  They  vary  much  in  size ;  in  England  they 
are  from  10  to  20  tons  capacity ;  in  Germany  larger  ones  are  used. 

The  condenser  consists  of  a  cast-  or  wrought-iron  or  lead  worm, 
placed  in  a  tank  of  water.  A  steam  pipe  is  arranged  to  warm  the 
water,  if  necessary. 

While  the  still  is  yet  hot  from  the  previous  distillation,  the  tar 
is  run  in.  Since  the  large  mass  of  cold  tar  requires  some  time  for 
heating,  the  fire  is  started  when  the  still  is  half  full.  When  the  tar 
runs  from  the  tell-tale  pipe,  the  manhole  and  valves  are  closed,  and 
the  heat  raised  until  the  contents  begin  to  froth.  The  overflow 
pipe  is  then  opened,  and  any  ammoniacal  liquor  which  has  separated 
is  drawn  off.  The  heating  is  continued  carefully  until  the  still-head 
gets  warm,  and  puffs  of  vapor,  and  finally  drops  of  liquid,  begin  to 
come  from  the  condenser.  The  fire  is  then  moderated,  in  order  to 
prevent  boiling  over.  A  closed  receiver  is  placed  at  the  end  of  the 
condenser,  and  the  distillation  is  continued  very  slowly,  until  the 
temperature  reaches  105°  C.,  when,  as  a  rule,  the  first  receiver  is 
changed.  The  distillate  is  commonly  separated  as  follows  :  — 
First  runnings,  or  "  first  light  oil,"  to  105°  C. 
Light  oil  to  210°  C. 
Carbolic  oil,  to  240°  C, 


COAL-TAR  329 

Creosote  oil,  to  270°  C. 

Anthracene  oil  "  green  oil,"  above  270°  C. 

Sometimes  the  first  runnings  and  light  oil  are  collected  together 
until  the  temperature  reaches  170°  C. ;  and  the  distillate  between 
170°  C.  and  230°  C.  is  taken  as  carbolic  oil.  The  temperature  at 
which  the  distillation  is  stopped  depends  upon  the  quantity  of  anthra- 
cene in  the  distillate  and  upon  whether  it  is  desired  to  produce  hard 
or  soft  pitch. 

The  first  runnings,  or  first  light  oil,  contain  water,  ammonium 
salts,  the  very  volatile  oils,  and  a  small  quantity  of  heavier  oils  car- 
ried over  mechanically.  After  this  distillate  has  run  for  some  time, 
it  nearly  ceases,  although  the  fire  is  now  increased.  This  is  known 
as  the  "  break,"  and  is  the  point  where  the  receiver  is  generally 
changed.  During  the  interval  a  peculiar  sputtering  noise  ("  rattles  ") 
is  heard  in  the  still,  caused  by  drops  of  condensed  water  falling  into 
the  tar,  which  is  now  considerably  above  110°  C. 

When  the  liquid  begins  to  run  from  the  condenser  again,  the 
"  second  light  oil  "  is  collected  until  the  temperature  of  the  tar  reaches 
210°  CM  or  until  the  distillate  equals  1.000  sp.  gr.  This  is  shown  by 
catching  some  of  it  in  a  glass  of  water;  if  it  forms  spherical  drops 
which  neither  sink  nor  rise  in  the  wrater,  but  float  at  whatever  point 
they  happen  to  fall,  the  receiver  should  be  changed.  During  this 
period  very  little  cooling  water  is  admitted  to  the  condenser,  so  that  it 
is  warmed  to  40°-50°  C. ;  the  water  is  then  cut  off  entirely. 

The  carbolic  oil  is  distilled  until  the  temperature  of  the  tar 
reaches  240°  C.,  or  until  a  few  drops  of  the  distillate  cooled  on  an 
iron  plate  show  crystals  of  naphthalene.  This  oil  contains  phenols, 
and  as  the  naphthalene  is  less  soluble  in  the  heavy  oils  than  in  the 
phenols,  its  crystallization  indicates  that  all  the  latter  have  distilled 
off.  The  warm  water  in  the  condenser  prevents  crystallization  in 
the  worm ;  towards  the  end  of  this  period  it  is  sometimes  necessary 
to  heat  the  water  by  a  steam  coil. 

The  receiver  is  again  changed,  and  the  "  creosote  oil  "  collected 
until  the  temperature  reaches  270°  C.  The  first  runnings  of  this 
contain  much  naphthalene,  but  later  the  quantity  present  is  small, 
and  remains  dissolved  in  the  heavy  oil.  This  distillate  is  the  least 
valuable  and  is  often  not  purified  further. 

The  anthracene  oil,  or  "  green  oil,"  collected  over  270°  C.,  con- 
tains anthracene,  the  most  valuable  constituent  of  the  tar.  The 
water  in  the  condenser  is  now  brought  to  the  boiling  point.  Super- 
heated steam  is  injected  into  the  hot  tar  in  the  still  to  aid  in  carry- 


330  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

ing  over  the  heavy  vapors.  The  process  is  generally  stopped  when 
the  distillate  becomes  "  gummy  " ;  on  cooling  it  has  about  the  con- 
sistency of  butter. 

The  pitch  left  in  the  still  is  a  thick,  viscous  mass  while  hot,  and 
if  run  out  immediately  will  take  fire  in  the  air.  After  cooling  a  few 
hours,  it  is  run  out  through  the  pitch  cock,  and,  when  cold,  hardens 
and  is  sold  as  "  hard  pitch."  But  the  still  must  be  emptied  while 
the  pitch  is  warm  enough  to  drain  out  completely,  for  if  any  is  left  in 
the  still  the  heat  radiating  from  the  brickwork  will  convert  it  into  coke, 
which  fastens  very  firmly  to  the  still  bottom  and  does  not  dissolve 
when  a  fresh  charge  of  tar  is  run  in.  To  facilitate  emptying  and  also 
to  supply  a  demand  for  "'soft  pitch,"  it  is  often  the  practice  after  the 
anthracene  oil  is  distilled,  to  pump  into  the  still  a  certain  amount  of 
creosote  or  carbolic  oil,  or  the  "  dead  oils  "  from  which  the  anthracene 
has  been  extracted.  This  mixes  with  the  hot  tar  and  produces  a  pitch 
of  any  desired  consistency,  according  to  the  quantity  of  oil  used. 

Stills  are  sometimes  provided  with  mechanical  stirring  apparatus 
to  prevent  the  pitch  from  burning  on  the  bottom,  and  to  assist  in 
mixing  it  with  the  oils  used  for  softening  it. 

The  crude  distillates  obtained  directly  from  the  tar  are  further 
purified  and  separated  into  commercial  products.  The  first  runnings 
contain  ammoniacal  liquor  and  naphtha,  which  are  usually  separated 
by  gravity.  The  former  is  put  with  the  gas  liquor  from  the  tar; 
the  latter  is  usually  refined  with  the  light  oil  distillate. 

The  light  oil  contains  benzene,  toluene,  and  xylene,  with  some 
thiophene,  phenols,  pyridine  bases,  and  heavy  oils.  It  is  distilled  in 
stills  much  like  those  used  for  tar,  but  smaller.  Two  fractions  are 
made,  naphtha,  which  distils  under  170°  C.,  being  further  purified; 
and  the  last  runnings,  which  are  put  with  the  carbolic  oil. 

The  naphtha  is  put  into  a  lead-lined  vessel  provided  with  an  agi- 
tator, and  thoroughly  mixed  with  dilute  caustic  soda  solution.  This 
combines  with  the  phenols,  which  are  thus  removed  when  the  soda  so- 
lution is  drawn  off.  After  washing  the  oil  with  water,  about  5  per  cent 
of  sulphuric  acid  (sp.  gr.  1.83)  is  added  and  agitated  with  the  oil,  the 
temperature  being  kept  low.  This  dissolves  thiophene,  unsaturated 
hydrocarbons  and  pyridines,  and  chars  and  destroys  other  matter. 
The  acid  tar  thus  formed  is  drawn  off  and  the  oil  washed  several  times 
with  water,  and  finally  with  caustic  soda  to  remove  all  the  acid.  The 
washed  oil  is  then  redistilled.  When  collected  up  to  110°  C.,  the  dis~ 
tillate  is  called  "  90  per  cent  benzol,"  since  that  amount  by  volume 
distils  below  100°  C.  It  contains  about  70  per  cent  pure  benzene, 


COAL-TAR  331 

24  per  cent  toluene,  and  some  xylene.  If  collected  up  to  140°  C.,  the 
distillate  is  known  as  "  50  per  cent  benzol,"  and  contains  about  46 
per  cent  pure  benzene.  Between  140°  C.  and  170°  C.  a  distillate  called 
"  solvent  naphtha  "  or  "  benzine  "  is  obtained.  This  consists  mainly 
of  xylenes,  cumenes,  etc.,  and  is  used  as  a  solvent  for  resins  and  rubber, 
for  thinning  paints,  and  to  wash  the  crude  anthracene  obtained  from 
the  anthracene  oil.  It  is  also  employed  to  enrich  illuminating  gas,  and 
as  a  cleansing  agent  for  grease-stained  fabrics.  It  must  not  be  confused 
with  petroleum  benzine  (p.  340),  which  is  of  different  composition. 

The  crude  50  or  90  per  cent  benzol  is  chiefly  employed  in  the 
coal-tar  dye  industry.  By  careful  distillation  in  a  rectifying  still, 
such  as  Coupier's  or  Sevalle's  (p.  12),  it  yields  pure  benzene,  boil- 
ing at  80-82°  C.,  toluene  at  110-112°  C.,  and  xylene,  137-143°  C. 

The  carbolic  oil  contains  phenols  and  naphthalene ;  after  cooling, 
the  oil  is  pressed  or  filtered  out  of  the  magma  of  crude  naphthalene 
crystals,  which  are  purified  by  treating  with  sulphuric  acid  and 
heating  to  destroy  the  phenol  left  in  them.  After  separating  the 
acid  tar  and  washing,  the  naphthalene  is  distilled  or  sublimed. 

The  oil  pressed  from  the  naphthalene  crystals  may  be  treated  by 
either  of  the  following  processes  to  recover  the  phenols  :  (a)  The  oil  is 
agitated  with  dilute  caustic  soda,  which  dissolves  the  phenols,  forming 
solution  of  "  sodium  carbolate."  This  separates  by  gravity  from  the 
undissolved  neutral  oils  and  is  drawn  off  and  decomposed  with  sul- 
phuric acid,  or  carbon  dioxide,  or  furnace  gases,  whereby  crude  carbolic 
acid  (phenol)  separates  as  an  oily  liquid,  from  which  crude  phenol  crys- 
tallizes on  chilling,  (b)  The  oil  may  be  heated  with  a  mixture  of  lime 
and  sodium  sulphate,  sodium  carbolate  being  formed  and  calcium  sul- 
phate precipitating.  After  the  impurities  have  settled,  the  solution  of 
phenols  (tar  acids)  is  decanted  and  sold  as  crude  carbolic  acid.  This 
is  purified  by  repeated  distillation  in  a  column  apparatus  of  iron  or 
copper,  with  zinc  condensers.  Sometimes  potassium  bichromate  and 
sulphuric  acid  are  put  into  the  still  to  oxidize  the  impurities.  Crystals 
of  phenol  separate  from  the  distillate  on  cooling,  while  the  cresols  re- 
main liquid.  The  phenol  is  separated  from  all  liquid  matter  by  a  cen- 
trifugal machine.  By  treating  the  alkaline  solution  of  phenols  with  an 
insufficient  quantity  of  acid,  the  cresols  are  precipitated  first  and  may 
be  separated,  the  phenol  being  separated  afterwards  with  more  acid. 

Crystallized  phenol,  C6H5OH,  melts  at  42°  C.,  but  the  presence  of 
a  very  little  water  causes  the  whole  mass  to  liquefy.  It  boils  at 
184°  C.,  and  can  be  distilled  unchanged.  Carbolic  acid  is  a  violent 
poison  and  has  a  penetrating  odor.  It  is  a  powerful  antiseptic, 


332  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

germicide,  and  disinfectant.  It  is  the  source  from  which  many  dyes, 
explosives,  and  medicinal  chemicals  are  prepared.  When  dissolved  in 
soap,  the  crude  tar  acids  are  often  used  as  antiseptics  under  the  names 
lysol  and  kreolin ;  these  are  soluble  in  water  or  emulsify  with  it. 

The  creosote  oil  also  furnishes  naphthalene,  which  crystallizes  on 
cooling.  It  is  filtered,  or  pressed  in  presses  which  have  steam-heated 
plates ;  the  crude  naphthalene  is  washed  with  caustic  soda  solution 
and  with  concentrated  acid,  and  is  distilled  or  sublimed;  the  oil 
contains  cresols  and  higher  phenols,  naphthol,  and  liquid  paraffine, 
which  have  but  little  value  and  are  not  separated.  It  is  chiefly  used 
for  preserving  ("  pickling  ")  timber  and  railroad  sleepers  ;  the 
timber  is  thoroughly  dried,  placed  in  tanks  from  which  the  air  is 
exhausted,  and  the  hot  creosote  oil  pumped  in  under  heavy  press- 
ure. A  small  amount  is  used  for  lubricant,  and  as  an  illuminant 
for  outdoor  work  where  smoke  is  of  no  consequence.  It  is  also 
used  as  fuel,  and  extensively  in  the  preparation  of  "  sheep  dips," 
liquids  used  for  destroying  ticks  and  vermin  on  sheep  and  cattle. 

Naphthalene  is  one  of  the  most  important  constituents  of  coal-tar, 
forming  over  5  per  cent  of  it.  It  forms  shining  white  platelike 
crystals,  which  melt  at  79°  C.,  and  boil  at  218°  C.  It  has  a  peculiar 
penetrating  odor,  and  is  much  used  instead  of  camphor  to  protect 
woolen  goods  and  furs  from  moths ;  it  is  also  used  to  prepare  naphthols, 
naphtylamines,  and  phthalic  acids  as  "  intermediates  "  for  the  manu- 
facture of  dyes.  Nitronaphthalene  is  employed  to  remove  the  " bloom  " 
from  mineral  oils  (p.  342). 

The  anthracene  oil,  or  "  green  oil,"  contains  about  10  per  cent 
anthracene,  Ci4Hio,  together  with  other  solid  hydrocarbons,  such  as 
phenanthrene,  chrysen,  carbazol,  paraffine,  and  liquid  oils  of  high 
boiling  points.  The  mass  is  cooled  until  the  solid  matter  has  crystal- 
lized, when  the  liquid  oils  are  removed  by  bag  filtering  or  by  a  filter 
press  or  centrifugal  machine.  The  crystalline  mass  so  obtained  is 
pressed  in  canvas  bags  in  a  hydraulic  press  at  a  temperature  of  40°  C. 
The  oils  expressed  are  then  again  chilled  to  a  low  temperature  and 
pressed,  or  are  redistilled  to  recover  more  anthracene ;  then  they  are 
mixed  with  the  creosote  oil  or  run  back  into  the  tar  still  to  soften  the 
pitch.  The  crude  30  per  cent  anthracene  from  the  press  is  pulver- 
ized and  washed  with  creosote  oil  or  with  solvent  naphtha  from  the 
light  oils,  which  dissolves  much  of  the  contaminating  substances,  but 
does  not  remove  carbazol.  The  magma  is  "  centriffed  "  or  pressed ; 
the  liquid  separated  is  distilled  to  recover  the  naphtha,  and  the  residue 
of  phenanthrene,  having  little  value,  is  usually  burned  for  lampblack. 


COAL-TAR 


333 


By  these  washings,  the  anthracene  is  raised  to  about  50  per  cent, 
when  it  is  sold  to  the  alizarine  manufacturer.  For  further  purifica- 
tion, it  is  washed  with  caustic  potash  to  remove  carbazol,  and  then 
it  is  sublimed  in  an  atmosphere  of  superheated  steam.  It  forms 
white  plates  of  pearly  lustre,  melting  at  213°  C.  and  boiling  at  360°  C. 
It  is  employed  chiefly  in  the  preparation  of  artificial  alizarine. 

The  pitch  left  in  the  still  is  either  hard  or  soft,  as  described  on 
page  330.  If  so  soft  that  it  remains  liquid  when  cold,  it  is  often  used 
as  a  black  varnish  for  painting  metal  work  and  wood,  or  for  making 
tarred  paper  or  roofing  paper.  Soft  pitch  is  used  as  a  binder  in 
preparing  fuel  "  briquettes  "  from  coal  dust.  Pitch  is  also  mixed 
with  asphalt  for  making  sidewalks  and  pavements.  Soft  pitch  softens 
at  about  38MO°  C.  and  melts  at  60°  C.  When  a  small  piece  is 
chewed,  it  coheres  together  like  gum.  Hard  pitch  softens  at  75°- 
80°  C.,  and  melts  above  120°  C.  When  chewed,  it  pulverizes  into 
a  non-cohesive  powder  in  the  mouth. 

The  yield  of  crude  products  from  tars  is  about  as  follows :  — 


GAS-WORKS  TAR* 

COKE-OVEN  TAH  f 

Ammoniacal  liquor               .... 

181  % 

2.3  % 

Light  oils      .    *     P"  .     »     . 

1  65 

37 

Middle  oils  (carbolic  oil)     .... 
Heavy  oil  (creosote  oil)  

10.66 

8.18 

9.8 
12.0 

Anthracene  oil  

14.05 

4.3 

Pitch  

61.16 

67.0 

Loss 

248 

09 

The  yield  of  purified  products  from  tar  is  about  as  follows :  {  — 
Benzol  and  toluol     .     .     .     0.22%  Cresols    .     .     .     .     1.13% 

Xylol  and  solvent  naphtha     0.62  Naphthalene    .     .     6.40 

Phenol  .     .     .    -,     .     .     .     0.40  Anthracene  (pure)     0.44 

REFERENCES 

Das  Anthracene  und  seine  Derivate.  G.  Auerbach,  Braunschweig,  1880. 
Die  Chemie  des  Steinkohlentheers.  Gustav  Schultz,  Braunschweig,  1890. 
Die  technische  Verwerthung  des  Steinkohlentheers.  G.  Thenius,  Vienna, 

1887. 

Coal-Tar  and  Ammonia.     Geo.  Lunge,  4th  ed.,  London,  1909. 
Die  Industrie  des  Steinkohlentheers  und  des  Ammoniaks.     G.  Lunge  und 

H.  Kohler.    2  vols.    Braunschweig,  1912. 
Coal  Gas  Residuals.     Frederick  Wagner.     New  York,  1914. 

*  Schniewindt,  Mineral  Industry,  1902,  152. 

t  Lunge,  Coal-tar  and  Ammonia,  I,  116. 

t  Heusler,  Chem.  Technologic,  Leipzig,  1905,  188. 


MINERAL  OILS 

THE  PETROLEUM  INDUSTRY 

Petroleum  is  widely  distributed,  being  found  in  many  places  in 
sufficient  quantities  for  profitable  working.  The  principal  deposits 
in  America  are  located  in  Pennsylvania,  New  York,  Ohio,  West  Vir- 
ginia, Indiana,  Illinois,  Kansas,  Kentucky,  Oklahoma,  Louisiana, 
Texas,  California,  Colorado,  Mexico,  and  Canada.  The  next  in  im- 
portance to  the  American  oil  fields  are  the  Russian,  in  the  Baku  dis- 
trict around  the  Caspian  Sea,  in  the  Caucasus  mountains,  and  along 
the  northeast  coast  of  the  Black  Sea.  Less  important  deposits  occur 
in  Persia,  Burmah,  Borneo,  Galicia,  and  Roumania.  Small  deposits 
are  worked  in  Germany,  Hungary,  Algiers,  Japan,  Venezuela,  New 
Zealand,  and  in  some  of  the  islands  of  the  Pacific. 

Petroleum  occurs  in  all  geological  formations  from  the  Silurian 
to  the  Tertiary,  the  New  York  and  Pennsylvania  deposits  being  in 
the  Devonian  and  Upper  Silurian,  the  Colorado  fields  in  the  Creta- 
ceous, and  those  in  California  in  the  Miocene  epoch  or  Middle  Ter- 
tiary. The  Russian,  Galician,  and  Indian  oils  are  chiefly  in  the 
Tertiary.  In  all  cases,  the  strata  in  which  it  is  found  are  horizontal 
or  but  slightly  inclined,  usually  not  over  30°.  It  is  generally  found 
in  sandstones  or  conglomerates,  called  "  oil  sands,"  overlaid  with  an 
impervious  shale  or  slate.  Frequently  several  layers  of  sandstone 
are  struck,  lying  between  beds  of  the  shale. 

The  origin  of  petroleum  has  been  the  subject  of  much  study  by 
many  eminent  chemists.  Berthelot  regarded  it  as  the  product  of 
the  action  of  steam  and  carbon  dioxide  on  the  alkali  metals.  Men- 
deleeff  supposed  it  resulted  from  the  decomposition  of  metallic  car- 
bides by  water.  This  necessitates  the  acceptance  of  La  Place's 
theory  of  the  formation  of  the  earth,  and  the  assumption  that  heavy 
metals,  such  as  iron,  were  among  the  first  substances  to  condense  into 
the  liquid  and  solid  state,  thus  forming  the  central  portion  of  the 
earth;  and  that  these  metals  then  combined  with  the  carbon  from 
the  surrounding  atmosphere  to  form  carbides,  which  were  after- 
wards decomposed  by  water,  from  the  cooled  surface,  which  perco- 
lated down  through  cracks  and  fissures  caused  by  the  cooling  and 
shrinkage  of  the  earth's  crust.  Thus  hydrocarbons  were  formed  and 
metallic  oxides  left  in  the  earth.  This  theory  requires  that  all  petro- 

334 


MINERAL  OILS  335 

leums  have  approximately  the  same  composition,  in  whatever  forma- 
tion they  are  found,  but  this  is  not  the  case. 

Another  hypothesis  supposes  petroleum  to  be  of  organic  origin. 
Here  again  are  several  theories  as  to  the  formation  of  the  oil  from 
the  vegetable  or  animal  remains.  One  is  that  the  organic  matter, 
probably  consisting  of  vegetable  matter  and  mollusks,  decomposed 
under  salt  water  with  exclusion  of  oxygen  and  at  a  rather  low  tem- 
perature.* Another,  that  only  animal  matter  is  the  basis  of  the  oil 
and  that  the  nitrogen  of  the  animal  tissues  escaped  as  ammonia  or 
other  nitrogen  compounds,  and  that  the  remaining  fat  was  subjected 
to  a  species  of  dry  distillation  under  great  pressure,  yielding  crude 
petroleum,  f  There  is  reason  to  believe  that  the  New  York,  Pennsyl- 
vania, and  Ohio  petroleums  are  of  vegetable  origin,  {  but  those  of 
California,  §  Texas,  and  some  others  contain  nitrogen  and  are  found 
in  rocks  filled  with  animal  remains. 

The  crude  oil  usually  consists  of  hydrocarbons,  present  in  homol- 
ogous series,  though  oils  from  different  localities  show  differences 
in  these  series.  The  Pennsylvania  oils  contain  members  of  the  marsh 
gas  series  with  the  general  formulas,  CnH2n+2  ;  all  of  these,  from  methane, 
CHi,  up  to  solid  paraffines  with  C2yH56,  have  been  isolated  from  these 
oils.  Also,  small  amounts  of  the  olefine  series,  CnH2n,  and  the  ben- 
zene series,  CnH2n-6,  and  in  some  oils,  sulphur  and  nitrogen  have 
been  found.  Various  crude  oils  from  California,  Texas,  Oklahoma,  and 
Kansas  contain  asphaltum,  as  well  as  paraffine.  The  Russian  oils 
consist  largely  of  the  naphthene  series,  general  formula  CnH2n,  isomeric 
with  the  olefines,  but  differing  from  them  in  their  properties,  so  the 
refining  is  not  the  same  as  that  of  the  American  oils. 

In  many  places  crude  oil  comes  to  the  surface  in  small  quantities, 
mixed  with  the  water  from  springs,  the  first  discoveries  having  been 
reported  as  "  oil  springs."  The  explorers  in  central  New  York,  as 
early  as  1630,  mentioned  an  Indian  remedy  containing  petroleum. 
Later  it  was  sold  as  "  Seneca  oil,"  by  the  Seneca  Indians.  Their 
method  of  collecting  it  was  to  spread  blankets  on  the  surface  of  the 
water  on  which  the  oil  was  floating,  wringing  it  out  when  the  blanket 
became  saturated.  If  the  layer  of  oil  was  thick  enough,  it  was 
skimmed  off  with  a  flat  board. 

About  the  middle  of  the  19th  century,  petroleum  from  various  parts 

*  Phillips.     Am.  Chem.  Jour,,  16,  409-429. 
f  Engler,  Ber.,  1888,  1816;    1889,  592. 

J  Orton.  Report  on  Occurrence  of  Petroleum,  Natural  Gas,  and  Asphalt  in 
Western  Kentucky.  1891. 

§  Peckham.     Am.  Jour.  Science,  48.     (1894.) 


336  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

of  the  world  had  begun  to  attract  some  attention,  and  crude  methods 
of  refining  it  had  been  devised;  in  some  few  instances  this  purified 
oil  was  being  used  for  illuminating.  But  none  of  these  efforts  had 
been  very  successful,  and  it  was  not  until  1859,  when  Mr.  Drake 
drilled  the  first  productive  oil  well  near  Titusville,  Pa.,  that  the  real 
development  of  the  petroleum  industry  began.*  The  Russian, 
Indian,  and  Galician  oils  were  mentioned  by  explorers  during  and  be- 
fore the  Middle  Ages,  but  the  industries  have  never  been  developed 
to  any  great  extent,  until  within  the  last  thirty  years,  when  the 
Russian  fields  have  become  very  important. 

The  crude  oil  is  obtained  by  boring  tube  wells  through  the  shale 
into  the  sand  rock.  There  is  no  certainty  beforehand  that  a  well 
will  yield  oil,  and,  indeed,  about  one-fifth  of  those  bored  in  this  country 
produced  none  ;  these  are  called  "  dry  holes." 

The  machinery  used  in  oil-well  drilling  is  very  ingenious,  and  a 
great  number  of  special  devices  have  been  invented  to  overcome  the 
numerous  obstacles  encountered.  Only  the  principal  tools  can  be 
mentioned  here.  The  chief  one  is  the  "  centre-bit  "  (Fig. 
101),  a  chisel-shaped  piece  of  steel  4  feet  long  and  weighing 
about  300  Ibs.,  the  cutting  edge  of  which  is  nearly  as  wide 
as  the  diameter  of  the  well.  Above  the  centre-bit 
is  the  "auger-stem,"  a  rigid  bar  from  12  to  45  feet 
long,  to  which  the  bit  is  screwed.  Its  chief  purpose 
is  to  guide  the  bit  and  keep  the  hole  straight;  it 
also  adds  weight  to  the  drill.  Next  above  the 
auger-stem  is  a  peculiar  piece  of  apparatus  called  the  "  jars  " 
(Fig.  102).  It  consists  of  two  links  of  steel  which  have  a  slid- 
ing motion,  one  within  the  other,  of  from  20  to  24  inches. 
The_  object  of  this  is  as  follows :  the  centre-bit  frequently 
becomes  fastened  in  the  hole,  either  by  fragments  of  broken 
rock  acting  as  wedges  between  it  and  the  sides  of  the  well, 
or  through  sinking  into  a  seam  in  the  rock.  Any  attempt  to 
loosen  it  by  a  steady  upward  pull  would  break  the  rope,  but 
a  sudden  upward  shock  is  generally  sufficient  to  loosen  it.  Fl0-102- 
This  is  obtained  by  the  movable  links  of  the  jars.  But  they  are  not 
allowed  to  close  completely,  and  so  give  a  downward  stroke,  unless 
the  tools  become  fast  in  the  well.  Above  the  jars  is  a  long,  heavy  steel 
bar  called  the  "  sinker-bar."  Through  its  momentum  this  gives  greater 
effect  to  the  action  of  the  jars.  To  the  top  of  the  sinker-bar  the  rope 

*  A  period  of  wild  excitement  and  speculation  followed,  the  description  of  which 
by  Peckham,  Crew,  and  others,  is  very  interesting  reading. 


MINERAL   OILS  337 

is  attached,  by  which  the  entire  mass  is  lifted  and  dropped,  just  as  a 
pile-driver  is  operated.  The  drop  allowed  for  each  stroke  of  the  bit 
is  about  two  feet.  The  rope  is  fastened  to  the  "  temper-screw,'* 
which  lowers  the  tools  slightly  as  the  rock  is  cut  away  by  each  blow  of 
the  bit,  and  turns  them  in  the  hole  so  that  the  next  cut  shall  be  at  a 
slight  angle  to  the  last  one.  When  all  screwed  together,  the  drilling 
tools  form  a  rod  about  60  feet  long  and  weighing  about  a  ton. 

Over  the  spot  where  the  well  is  to  be  drilled  a  timber  or  steel  struc- 
ture is  built,  called  the  "  derrick  " ;  this  is  from  35  to  80  feet  high, 
and  from  12  to  15  feet  square  at  the  bottom,  tapering  to  about  5  feet 
square  at  the  top.  On  the  floor  of  the  derrick  is  the  windlass  for 
handling  the  drilling  tools,  the  rope  passing  over  a  small  wheel  at  the 
top.  During  the  drilling  the  rope  passes  through  a  clutch  at  the  end 
of  a  large  walking-beam,  driven  by  the  engine,  imparting  a  rapid  up- 
and-down  motion  to  the  tools. 

An  iron  "  drive-pipe  "  is  sunk  through  the  drift  and  clay  to  the 
solid  bed-rock.  If  the  latter  is  within  15  or  20  feet  of  the  surface,  a 
shaft  6  or  8  feet  square  is  sometimes  dug  down  to  it.  Then  the 
drilling  of  the  well  proper  begins,  which  is  usually  7|  inches  in  diam- 
eter to  the  bottom  of  the  water-bearing  strata..  Then  the  hole 
is  decreased  to  5f  inches  diameter,  and  a  tube,  called  the  "  casing," 
is  put  down ;  this  is  provided  with  a  rubber  or  leather  collar  to  fit 
closely  against  the  shoulder  formed  where  the  diameter  of  the  well 
decreases,  making  a  water-tight  joint.  Then  the  hole  is  continued 
to  the  oil-bearing  strata,  by  means  of  a  5j-inch  bit. 

At  frequent  intervals  it  is  necessary  to  remove  the  mud  and  splinters 
of  rock.  This  is  done  by  the  "  sand-pump,"  or  "  bailer,"  which  is  a 
long  metal  tube,  having  a  valve  in  the  bottom.  It  is  lowered  until 
a  pin  on  the  under  side  of  the  valve  strikes  the  bottom  of  the  well. 
The  water,  which  is  always  present,  rushes  into  the  bailer,  drawing  with 
it  the  debris ;  then  the  tool  is  at  once  raised  and  the  valve  closes. 

It  is  customary  to  drill  some  distance  into  the  oil-bearing  stratum, 
and  sometimes  a  cavity  filled  with  gas,  oil,  and  water  is  struck.  The 
pressure  is  occasionally  so  great  as  to  drive  the  oil  to  the  surface,  some- 
times with  great  force.  Such  wells  are  called  "  gushers."  They  seldom 
continue  to  flow  for  more  than  a  few  days  or  weeks,  when  pumping 
must  be  employed.  Some  of  these  gushers  have  produced  enormous 
quantities  of  oil,  as  much  as  75,000  *  barrels  a  day  when  at  their  height. 

But  most  wells  do  not  gush,  and  it  is  now  customary  to  re- 
sort to  "  torpedoing,"  in  order  to  increase  the  yield  of  oil.  A  tin 
*  Mineral  Resources  of  the  United  States,  1902,  570. 


338  OUTLINES   OF   INDUSTRIAL   CHEMISTRY  . 

shell,  from  3  to  5  inches  in  diameter  and  from  5  to  20  feet  long,  is 
filled  with  nitroglycerine  and  lowered  to  the  bottom  of  the  well. 
On  top  of  the  can  is  a  percussion  cap,  which  is  fired  by  dropping  a 
piece  of  iron,  called  a  "  go-devil,"  weighing  several  pounds,  into  the 
well.  The  resulting  explosion  cracks  and  shivers  the  rock,  giving 
the  oil  a  better  opportunity  to  flow  into  the  well.  Very  often  a  well 
gushes  after  torpedoing,  and  measures  are  usually  taken  beforehand  to 
dispose  of  the  first  heavy  rush  of  oil  and  water. 

The  finished  well  is  prepared  for  pumping  by  lowering  a  2-inch 
pipe,  at  the  bottom  of  which  is  the  oil  pump,  worked  by  a  wooden  rod 
inside  the  pipe.      Fig.   103  shows  sections  through  a  pumping  and 
through  a  flowing  well.     In  a  flowing  well  no  pump 
rod  is  introduced,  but  the  space  between  the  casing 
and  tubing  is  tightly  closed  at  the  top,  in  order  to 
force  both  gas  and  oil  through  the  tubing. 

The  wells  range  in  depth  from  50  to  4000  feet,  the 
average  in  New  York  and  Pennsylvania  being  from 
1200  to  1800  feet.  The  cost  varies,  but  from  3000 
to  4000  dollars  is  about  the  average.  The  ordinary 
production  varies  from  one  to  several  hundred  barrels 
per  day. 

The  crude  oil  is  now  generally  carried  from  the 
wells  to  the  refineries  by  pipe-lines,  —  six-  or  eight- 
inch  pipe,  through  which  the  oil  is  pumped.  At  fre- 

FIG.  103.  .  . 

quent  intervals  along  the  pipe-lines  are  tanks  of  from 
30,000  to  40,000  barrels  capacity,  in  which  the  oil  is  stored  until  wanted 
for  refining.  This  system  mixes  all  varieties  of  oils ;  hence,  if  a  special 
kind  is  required,  it  must  be  transported  in  tank  cars  or  in  barrels. 

Crude  petroleum  is  an  oily  liquid  varying  in  color  from  greenish 
brown  to  nearly  black ;  some  varieties  are  reddish  brown  or  orange 
when  viewed  by  transmitted  light.  Nearly  all  show  some  fluo- 
rescence, and  have  a  rather  unpleasant  odor.  The  specific  gravity 
varies  from  0.782  to  above  0.850,  in  oils  from  different  localities.  As 
it  comes  from  the  well,  more  or  less  gas  is  dissolved  in  it,  consisting 
chiefly  of  marsh  gas,  CH4 ;  ethane,  C2H6 ;  propane,  CaHg ;  and  butane, 
C-iHio.  A  very  small  amount  of  phosphorus  is  often  present,  but 
seldom  more  than  0.05  per  cent.  The  oils  from  Ohio  and  Canada 
have  an  unpleasant  odor,  because  they  contain  some  sulphur  com- 
pounds. Sand  and  water  are  also  mixed  with  the  crude  oil,  but  these 
settle  on  standing  in  the  storage  tanks. 

In  order  to  separate  the  various  products  from  the  crude  oil,  it  is 


MINERAL  OILS 


339 


subjected  to  fractiohal  distillation.  The  higher  the  percentage  of 
the  lighter  oils,  the  more  profitable  for  the  refiner ;  but  many  crude 
oils  are  distilled  only  for  the  lubricating  oils.  A  few  may  be  used 
as  lubricants  without  distilling.  Considerable  petroleum  is  used  for 
fuel,  but  this  is  being  replaced  by  the  residuum  from  which  the  more 
valuable  light  oils  have  been  separated. 

Refining  consists  in  the  separation  and  purification  of  the  market- 
able products  of  the  crude  oil,  which  is  usually  separated  into  about 
five  portions.  These  are  naphthas,  illuminating  oils,  lubricating  oils, 
paraffines,  and  coke.  The  process  is  usually  Worked  in  two  stages  :  the 
distillation  and  refining  first  of  the  light  oils,  and  then  of  the  heavy  oils. 
It  is  only  in  the  large  refineries  that  both  processes  are  carried  out ;  usu- 
ally one  refiner  produces  the  naphthas,  burning  oils,  and  "  residuum," 
and  another  starts  with  the  residuum  and  finishes  the  process. 

For  distilling  the  light  oils,  the  cylindrical  or  horizontal  still  (Fig. 
104)  is  used ;  this  is  30  to  40  feet  long  by  12  or  15  feet  in  diameter, 


FIG.  104. 

* 

and  is  set  in  a  brick  furnace,  with  the  upper  half  of  the  still  exposed 
to  the  air.  It  holds  600  to  750  barrels,  and  is  provided  with  steam 
coils  and  arrangements  for  blowing  in  free  steam  to  carry  on  the  pro- 
cess as  a  steam  distillation  if  desired. 

The  condensers  are  long  straight  pipes  set  in  troughs  through  which 
water  flows,  or  they  are  coils  set  in  tanks  of  cold  water.  They  are  so 
arranged  that  the  distillates  are  delivered  at  some  distance  from  the  still, 
to  diminish  the  fire  risk.  Each  pipe  is  usually  provided  with  a  trap  by 
which  the  gases  (passing  over  with  the  oil  vapors)  are  collected  and  then 
led  under  the  still  and  burned,  thus  economizing  fuel.  Sometimes  the 
veryjight  oils  are  burned  with  the  gases,  but  they  are  usually  condensed, 
forming  the  "  benzine  distillate,"  or  crude  naphtha.  This  is  stopped 
when  the  gravity  reaches  62°  Be.  (sp.  gr.  0.729).  Then  comes  the  kero- 
sene, or  burning  oil  distillate,  until  the  gravity  equals  0.790,  or  for  heavy 
illuminating  oils,  0.820.  Here  the  distillation  is  stopped  and  the  resid- 
uum drawn  off,  to  be  distilled  for  lubricating  oils,  in  the  "tar  stills." 


340  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

At  high  temperatures  oils  undergo  decomposition ;  the  heavy  oils 
tend  to  split  off  gas,  hydrocarbons  and  carbon,  forming  lighter  oils ; 
these  reactions  are  reversible.  The  process  is  called  "cracking"* 
and  the  reactions  are  complex,  the  number  of  products  formed  being 
quite  large.  The  heavy  oils  decompose  into  paraffines  and  olefines  of 
lower  boiling  points  and  hydrocarbons  of  the  aromatic  series  may  also 
be  produced.  As  an  example  of  what  may,  perhaps,  take  place  the 
hydrocarbon  CigHss  (octadecane),  boiling  at  317°  C,  may  be  assumed 
to  decompose  into  Ci0H22  (decane),  boiling  at  173°,  and  C7Hi6  (heptane), 
boiling  at  98°,  and  carbon ;  or  it  may  form  a  paraffine  and  an  define, 
e.g.  C8Hi8  (octane),  boiling  at  125°,  and  Ci0H2o  (decylene),  boiling  at 
172°.  The  lower  boiling  product  would  be  put  with  the  naphtha  dis- 
tillate, and  the  higher  boiling  would  form  a  part  of  the  burning  oil. 

During  the  course  of  the  reactions  certain  amounts  of  the  aromatic 
hydrocarbons  are  formed  in  the  order,  cymene,  xylene,  toluene,  benzene, 
naphthalene,  and  anthracene ;  these  substances  are  produced  progressively 
each  by  the  decomposition  of  the  one  preceding,  the  reactions  progressing 
further  in  the  direction  indicated,  the  higher  the  temperature.  Thus  the 
formation  of  aromatic  bodies  in  the  distillation  of  coal  is  also  explained, 
and  the  conditions  indicated  under  which  the  formation  of  the  individual 
hydrocarbons  will  be  a  maximum.  Rittman  has  succeeded  in  so  controlling 
the  temperatures  and  pressures  of  the  decompositions  that  the  artificial 
manufacture  of  gasolines  and  benzenes  becomes  possible. 

The  still,  as  already  shown,  has  its  upper  part  exposed  and  thus 
cooled  by  the  air ;  a  column  loosely  packed  with  stones  is  set  above 
the  still  and  the  vapors  pass  into  it ;  often  a  dephlegmator  is  also 
used.  The  heavy  oil  vapors  partly  condense  on  these  cooler  surfaces 
and  fall  back  into  the  boiling  residuum,  which  is  much  hotter  than 
their  boiling  points,  the  oils  of  high  molecular  weight  decompose  into 
into  bodies  of  lower  boiling  points,  while  some  carbon  separates  and 
forms  a  coke  in  the  still.  The  several  distillates  from  the  crude  oil 
are  redistilled  and  divided  into  further  subdivisions. 

The  benzine  distillate  yieldsf  :  — 

Cymogene,   B.  P.  =    32°  F.        Sp.  Gr.  =  0.590-0.610  ] 
Rhigolene,    B.  P.  =    60°  F.        Sp.  Gr.  =  0.625-0.631  ° 

Gasoline,       B.  P.  =  115°  F.        Sp.  Gr.  =  0.635-0.666 
C  Naphtha  (Benzine)  B.  P.  =  122°-140°  F.      Sp.  Gr.  =  0.678-0.700. 
B  Naphtha,  Sp.  Gr.  =  0.714-0.718. 

A  Naphtha  (Petroleum  naphtha),  Sp.  Gr.  =  0.741-0.745. 

*  The  history  of  the  discovery  of  this  process  is  given  in  chap,  iii  of  Petroleum 
Distillation,  by  A.  N.  Leet,  New  York,  1884. 

|  Boverton  Redwood  —  Groves  and  Thorp's  Chemical  Technology,  Vol.  II. 


MINERAL  OILS  341 

The  burning  oil  distillate  yields  :  — 

110°  fire  test  burning  oil  ("  Standard  white  ").  1  . 

120°  fire  test  burning  oil  ("  Prime  white  ").       }       P° 
150°  fire  test  burning  oil  ("  Water  white  "). 

The  residuum  from  the  above  distillation  is  transferred  to  the 
tar  still,  or  if  the  distillation  has  been  carried  on  under  vacuum,  it  is 
known  as  "  reduced  oil,"  and  is  used  to  make  fine  lubricating  oils  or 
vaseline. 

The  tar  stills  are  cylindrical,  and  are  set  in  much  the  same  way 
as  those  already  described,  but  are  encased  in  brickwork  almost  to 
the  top.  They  are  provided  with  pipes  for  introducing  superheated 
steam,  and  are  much  smaller  than  the  crude  oil  stills. 

The  first  distillate  is  collected  until  the  gravity  is  about  38°  Be. 
(0.834  sp.  gr.),  and  is  mixed  with  the  next  charge  of  crude  oil,  or 
washed  with  acid  and  soda  and  refined  for  burning  oil.  Then  follow 
several  distillates  of  increasing  color  and  density,  which  are  purified 
as  described  below,  and  treated  to  separate  the  paraffine  wax  and 
lubricating  oils.  The  distillation  is  carried  on  until  the  still  bottom 
is  red-hot,  when  a  gummy  yellow  distillate,  called  "  yellow  wax,"  is 
collected.  This  contains  anthracene  and  other  hydrocarbons  of  high 
molecular  weight.  The  residue  of  coke  is  valuable  for  electric  light 
carbons  and  other  electrical  purposes. 

The  fractions  collected  from  the  burning  oil  distillate  are  more  or 
less  yellow,  colored  by  tarry  matters,  which  would  collect  in  the 
lamp-wick  and  soon  choke  it.  To  remove  these  impurities,  the  oil  is 
put  into  an  "  agitator,"  a  large,  lead-lined,  iron  tank,  where  it  is 
mixed  with  from  1  to  2  per  cent  of  concentrated  sulphuric  acid,  and 
the  mixture  stirred  by  blowing  in  air  at  the  bottom.  The  acid  unites 
with  the  tarry  matters,  and  when  the  blast  is  stopped,  sinks  to  the 
bottom  and  is  drawn  off  as  "  sludge  acid."  Water  is  added,  and 
after  the  mixture  is  agitated,  is  drawn  off.  Next  a  solution  of  caus- 
tic soda  is  introduced  (about  1  per  cent),  and  the  contents  of  the  tank 
again  agitated.  Then  the  oil  is  again  washed  with  water  and  drawn 
into  the  settling  tanks,  where  the  suspended  water  settles  out,  leaving 
a  bright,  clear  oil.  These  tanks  are  very  shallow,  usually  only  about 
1  foot  or  15  inches  deep,  but  may  cover  an  area  of  20  by  30  feet. 
They  are  exposed  to  the  light  and  air,  and  usually  contain  steam 
coils  for  warming  the  oil  in  winter. 

If  the  oil  is  now  found  to  have  too  low  a  flash  point  (p.  344), 
it  is  run  through  a  "  sprayer,"  an  upright  pipe  with  cross-arms  of 


342  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

small  perforated  pipe,  through  which  the  oil  is  forced  into  the  air  in 
fine  jets  or  spray ;  after  falling  some  distance,  it  is  collected  in  tanks. 
By  this  exposure  to  air,  any  light  oils,  such  as  benzine  or  naphtha, 
are  volatilized,  and  the  flash  point  thus  raised.  But  spraying  is  less 
frequently  necessary  now,  since  more  care  is  taken  in  the  original 
distilling. 

Instead  of  washing,  some  kerosenes  are  redistilled,  but  this  gen- 
erally fails  to  remove  all  the  yellow  color,  though,  when  burned,  they 
do  not  form  a  crust  on  the  wick,  due  to  traces  of  caustic  soda  or  sodium 
sulphate. 

A  small  amount  of  burning  oil  of  very  high  fire  test  (about  300°  F.) 
is  made  by  treating  a  crude  oil  distillate  (0.823  to  0.846  sp.  gr.)  with 
a  very  large  proportion  (5  to  7  per  cent)  of  sulphuric  acid,  washing 
with  caustic  soda,  and  redistilling  with  caustic  soda  lye  in  the  still. 
This  oil  is  sold  as  mineral  colza,  mineral  seal,  and  mineral  sperm  oil. 

The  paraffine  oils  are  treated  with  acid  in  agitators  which  may  be 
heated  by  steam  pipes ;  they  are  washed  and  then  chilled  and  left 
several  hours  until  the  paraffine  crystallizes.  The  soft  mass  is  then 
put  into  canvas  bags  and  pressed  at  40°  F.  in  hydraulic  presses. 
The  crude  paraffine  cake  is  again  melted,  crystallized,  and  pressed. 
It  is  then  washed  with  a  little  benzine  and  pressed  once  more.  It 
is  finally  melted  and  filtered  hot  through  bone-char,  or  fuller's  earth 
and  on  cooling  forms  the  white  commercial  paraffine.  The  oils  ex- 
pressed are  lubricating  oils  of  various  grades. 

After  the  paraffine  is  removed,  some  of  the  lighter  lubricating  oils 
are  converted  into  "neutral  oils"  by  bone-char  or  fuller's  earth  filtra- 
tion and  exposure  to  sunlight  and  air,  to  remove  the  "  bloom,"  so  that 
they  may  be  used  to  adulterate  certain  animal  and  vegetable  oils.  It 
may  also  be  removed  chemically  by  adding  about  1  per  cent  of  nitro- 
naphthalene,  or  dinitrobenzol,  or  nitric  acid.  Bloom  has  no  injurious 
effect  upon  the  oil  or  machinery. 

Crude  petroleums  containing  sulphur  (e.g.  those  from  Ohio  and 
Canada)  are  more  difficult  to  refine,  and  consequently  were  formerly 
only  used  for  fuel.  Successful  methods  for  refining  them  are,  how- 
ever, now  in  use.  The  common  process  is  to  pass  the  vapors  from 
the  crude  oil  distillation  over  copper  oxide ;  or  to  collect  the  distil- 
lates from  the  crude  oil  separately  and  redistil  them  with  a  large 
excess  of  copper  oxide,  or  a  mixture  of  lead  and  copper  oxides  in  a 
still,  which  is  provided  with  an  agitator.  The  residue  consists  of  a 
mixture  of  tar,  copper  sulphide,  and  oxide.  This  is  pressed  and 
calcined  at  a  low  temperature,  the  combustion  of  sulphur  and  tar 


MINERAL  OILS  343 

furnishing  sufficient  heat.  The  final  product  is  copper  oxide,  which 
is  returned  to  the  process.  A  solution  of  litharge  in  caustic  soda  is 
sometimes  used  in  the  agitator  after  the  usual  acid  and  alkali  treat- 
ment, to  remove  the  sulphur,  but  this  is  not  always  a  success  ;  though 
it  destroys  the  offensive  odor,  traces  of  sulphur  sometimes  remain  and 
become  noticeable  on  burning. 

The  lighter  lubricating  oils  are  called  "  spindle  oils  "  and  are 
used  on  rapid-running  bearings.  "  Machinery  oils  "  form  the  middle 
grades,  and  "  cylinder  oils  "  are  the  heaviest.  Paraffine  in  lubricat- 
ing oils  is  said  to  reduce  its  viscosity  and  cause  it  to  become  gummy 
when  in  use. 

"  Reduced  oils  "  are  made  from  the  residuum  left  after  distilling 
the  burning  oils  from  some  crude  petroleums  by  the  aid  of  vacuum 
or  by  simply  exposing  certain  crude  oils  to  the  sun  and  air  in  shallow 
tanks  which  may  be  gently  heated  by  steam-coils  in  winter.  The 
very  light  oils  soon  evaporate  and  the  suspended  impurities  settle. 
Another  process  is  to  let  the  crude  oil  flow  in  thin  films  over  woollen 
blankets  suspended  in  warm  rooms ;  the  very  volatile  oils  evaporate 
and  much  of  the  suspended  matter  is  retained  by  the  cloth.  By 'these 
methods,  oils  are  obtained  which  are  entirely  free  from  any  decomposi- 
tion products  due  to  heating,  and  from  any  chemicals  such  as  are  used 
in  washing  and  bleaching  ordinary  lubricating  oils.  Crude  oils  of 
high  gravity  (below  32°  Be.)  are  usually  selected  for  this  purpose. 

Reduced  oils  are  valuable  lubricators  and  command  a  good  price. 
Sometimes  they  are  char-filtered  to  improve  their  color  and  quality. 

Vaseline  or  petrolatum  is  made  from  the  residuum  of  vacuum  dis- 
tilled crude  oils.  It  is  treated  with  acid  and  soda,  washed  and  char- 
filtered,  and  sometimes  redistilled  in  vacuum. 

The  Russian  petroleums  are  distilled  in  much  the  same  way  as 
the  American,  but  less  acid  is  used,  as  the  naphthenes  are  somewhat 
soluble  in  it.  It  is  found  practicable  to  use  continuous  stills,  as  the 
residuum  is  more  fluid  than  in  the  case  of  American  oils.  The  stills 
are  heated  by  separate  furnaces  and  connected  in  such  a  manner  that 
the  overflow  pipe  from  one  is  the  supply  pipe  for  the  next,  the  resid- 
uum from  the  last  passing  through  coils  placed  in  the  supply  tank, 
so  that  the  crude  oil  is  warm  when  it  enters  the  first  still.  By  care- 
ful regulation  of  the  heat  and  the  flow  of  oil,  each  still  can  be  made 
to  yield  a  distillate  of  constant  gravity. 

Russian  petroleum  yields  about  38  per  cent  illuminating  oils, 
which  is  lower  than  the  Pennsylvania  oils.  Since  fuel  is  scarce,  the 
residuum,  called  astatki,  is  burned  in  special  burners  and  furnaces. 


344 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


The  yield  of  lubricating  oils  is  large,  being  nearly  36  per  cent.     They 
are  said  to  be  superior  to  American  lubricators  for  use  in  cold  countries. 

Oil-testing.  —  The  usual  test  for  kerosene  is  the  flame  test,  i.e.  the 
determination  of  the  temperature  at  which  the  vapors  take  fire  when  mixed 
with  air.  The  point  usually  taken  is  the  "  flash  point,"  the  temperature 
at  which  the  oil  gives  off  sufficient  vapor  to  form  a  momentary  flash  when 
a  small  flame  is  brought  near  its  surface.  The  "  fire  test "  determines  the 
temperature  at  which  the  oil  gives  oft  enough  vapor  to  maintain  a  continu- 
ous flame  if  ignited  ;  in  other  words,  it  shows  the  temperature  at  which  the 
oil  burns  in  the  air,  and  is  about  20°  F.  higher  than  the  flash  point.  Both 
the  flash  point  and  the  burning  point  are  lower  than  the  boiling  point. 

The  flash  point  is  determined  in  a  special  apparatus,  and  in  many 
states  and  countries  the  particular  instrument  and  its  dimensions  are 
specified  by  law.  In  this  country,  "  open  testers  "  are  largely  used,  but 
Abel's  "  closed  tester  "  has  become  very  popular,  and  is 
now  the  legal  instrument  in  some  of  the  states  and  in 
England  and  Germany.  There  are  many  forms  of  appa- 
ratus for  oil  testing,  but  the  two  above  mentioned  cover 
the  general  principles  involved  in  all.  Open  testers  do 
not  represent  the  conditions  prevailing  in  an  ordinary 
lamp ;  the  closed  tester  more  nearly  approaches  these, 
and  its  indication  is  usually  about  20°  F.  lower  than  that 
shown  by  the  open  tester. 

Tagliabue's  open  tester  (Fig.  105)  is  very  simple. 
A  copper  water  bath  (A),  heated  by  the  small  lamp  (B), 
contains  the  glass  dish  in  which  the  oil  to  be  tested  is 
placed.  A  delicate  thermometer  (E) 
is  hung  to  dip  into  the  oil.  Some- 
times a  stirring  apparatus  is  pro- 
vided for  both  the  water  bath  and 
the  oil.  The  water  bath  is  slowly 
heated,  and  at  regular  intervals  of 
temperature  a  lighted  match  or  small 
gas  flame  is  passed  half  an  inch 
above  the  surface  of  the  oil.  The 
temperature  at  which  a  flame  passes  completely  over 
the  surface  is  noted  as  the  flash  point.  The  heating  is 
usually  continued  until  the  oil  catches  fire  on  applying 
the  light,  when  the  temperature  is  taken  as  the  burn- 
ing point.  The  apparatus  is  rather  crude  and  is  open 
to  errors. 

Abel's  closed  tester  (Fig.  106)  is  more  complicated, 
but  obviates  some  of  the  errors  of  the  open  cup.  It 
consists  of  a  copper  cylinder  (K,  K)  in  which  is  the 
water  bath  (F).  In  the  upper  part  of  the  water  bath  is 
an  air  chamber  (B)  in  which  is  suspended  the  copper 
vessel  (A)  carrying  the  oil.  All  these  vessels  are  provided  with  close-fitting 
covers.  The  cover  of  (A)  has  three  openings  which  may  be  opened  or 


FIG.  105. 


FIG.  106. 


MINERAL  OILS  345 

closed  by  a  small  lever.  The  cover  also  carries  the  thermometer  (D), 
dipping  into  the  oil,  and  a  small  lamp  or  gas  flame  set  on  an  axis  at 
(C),  so  that  the  flame  may  be  brought  directly  over  the  middle  open- 
ing in  the  cover.  Usually  the  lever  which  moves  the  cover  of  the  opening 
simultaneously  turns  the  flame  down  to  it.  The  thermometer  (E)  dips 
into  the  water  bath,  which  is  heated  to  54°  C.  before  the  oil  is  intro- 
duced into  (A).  When  the  thermometer  (D)  registers  18°-19°  C.  the  test- 
ing is  begun,  and  repeated  with  each  rise  of  a  degree,  until  the  flash  is 
seen.  This  instrument  is  officially  used  in  Germany,  the  lever  being 
run  by  clock-work.  It  is  also  used  in  England,  the  law  requiring  a  flash 
test  of  73°  F.,  which  is  rather  low  for  safety ;  it  should  not  be  under 
100°  F.  In  this  country,  each  state  has  its  own  standard.  Some  require 
150°  F.  fire  test  in  open  cups,  and  others  110°  F.  Most  states  fix  110°  F. 
flash  test. 

Lubricating  oils  are  usually  tested  for  viscosity,  gravity,  flash,  and 
burning  points,  congealing  point,  and  color.  The  gravity  is  usually 
determined  with  the  hydrometer  or  Westphal  balance.  In  this  country, 
the  Baume  instrument  is  almost  always  used. 

Viscosity  is  determined  by  relative  tests,  e.g.  the  rate  of  flow  of  the 
oil  through  a  capillary  tube  or  narrow  opening,  as  compared  with  the 
rate  of  flow  of  pure  sperm  oil  through  the  same  tube  or  opening.  Tem- 
perature is  here  a  very  important  factor. 

The  congealing  point,  or  "  cold  test,"  determines  the  temperature 
at  which  the  oil  becomes  pasty  or  solid  through  the  crystallization  of 
dissolved  paraffine  or  other  matter.  This  test  is  of  great  moment  if 
the  lubricators  are  to  be  used  in  cold  climates. 

Color  tests  are  chiefly  made  on  oils  intended  for  export,  by  com- 
paring a  tube  full  of  the  oil  with  standard  glass  plates  of  various  tints, 
in  a  colorimeter.  For  burning  oils  the  colors  range  from  pale  yellow  or 
straw  to  water  white. 

Certain  animal  and  vegetable  oils,  when  soaked  up  in  waste,  will 
take  fire  on  standing.  This  is  especially  true  of  linseed,  cotton-seed, 
corn,  lard,  and  neatsfoot  oils,  and  is  caused  by  the  rise  in  temperature 
due  to  the  oxidation  of  the  oil.  If  from  40  to  50  per  cent  of  mineral 
oil  be  added  to  these  oils,  this  spontaneous  combustion  is  prevented 
to  a  great  extent.  This  is  one  of  the  uses  of  the  neutral  oils  (p.  342). 

SHALE  OIL  INDUSTRY 

In  Scotland,  Germany,  and  a  few  other  countries,  mineral  oils 
are  produced  by  the  destructive  distillation  of  certain  bituminous 
shales.  These  are  soft,  light  brown,  or  gray  rocks,  which  do  not 
contain  oil  as  such,  but  are  permeated  with  bitumen,  a  complex 
organic  substance  similar  to  pitch.  When  heated  in  retorts,  this 
decomposes  into  gas,  oily  products,  ammonia,  and  tar,  leaving  a 
carbonaceous  residue.  The  temperature  of  the  distillation  greatly 


346  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

influences  the  character  of  the  products,  a  low  temperature  affording 
an  increased  yield  of  oil. 

The  shale  is  broken  to  small  size  and  heated  to  a  low  red  heat  in 
vertical  retorts  into  which  steam  is  injected  to  assist  in  the  distilla- 
tion. Both  continuous  and  intermittent  systems  of  distillation  are  in 
use,  the  former  being  generally  employed  in  Scotland.  The  shale  is 
charged  at  the  top  of  the  retort  and  when  "  spent  "  is  drawn  while  still 
hot  upon  a  grate  beneath  the  retort,  where  its  carbonaceous  matter 
(amounting  to  10-15  per  cent)  is  burned,  thus  economizing  fuel. 

The  products  of  the  distillation  pass  through  a  series  of  pipes 
similar  to  the  hydraulic  main  and  condensers  of  the  coal-gas  manu- 
facture. The  light  naphtha  vapors  and  gas  pass  into  a  coke  tower 
through  which  heavy  paraffine  oil  trickles ;  this  absorbs  the  naphtha, 
while  the  gas  passes  on  and  is  burned  under  the  retorts.  In  the 
hydraulic  main  and  condensers  the  other  distillates  condense  in  two 
layers,  the  ammoniacal  liquor  below  and  the  tar  and  oil  above.  These 
are  separated  by  gravity.  The  ammonia  liquor  is  treated  in  the  same 
way  as  that  from  coal  gas  (p.  151).  The  oily  tar  (0.865  sp.  gr.)is 
distilled  in  much  the  same  way  as  crude  petroleum  until  only  solid 
coke  remains  in  the  still.  The  distillates  are  collected  together  as 
"  once-run  oil  "  and  washed  in  agitators  with  sulphuric  acid  and 
caustic  soda,  and  then  fractionally  distilled.  These  distillates  are 
each  purified,  yielding  commercial  naphtha,  burning  oils,  lubricator 
oils,  and  solid  paraffine. 

The  acid  tar  from  the  washing  yields  some  ammonium  sulphate, 
and  tarry  matter  which  is  used  for  fuel.  The  soda  tar  is  treated 
with  carbon  dioxide,  which  liberates  the  creosote,  used  for  the  same 
purpose  as  that  from  coal-tar.  The  carbonate  of  soda  solution  is 
causticized  and  used  again. 

OZOKERITE 

Ozokerite  is  a  natural,  paraffine-like  substance  containing  a  small 
quantity  of  oily  matter.  It  was  probably  formed  by  the  evaporation 
of  petroleum  until  the  more  volatile  oils  had  escaped.  It  occurs  in 
irregular  seams  and  masses  in  the  earth  in  Galicia,  in  the  Caucasus, 
in  Utah,  and  in  Colorado.  In  Galicia  it  is  mined  by  sinking  shafts 
and  drifting,  following  the  seams.  The  wax  is  separated  from  the 
earthy  impurities  by  hand  picking  and  by  washing,  the  wax  being 
lighter  than  water  and  rising  to  the  surface.  The  residue  is  boiled 
with  water  to  melt  out  the  remaining  wax,  which  is  skimmed  from 
the  surface.  Extraction  with  benzene  is  also  employed. 


MINERAL  OILS  347 

The  wax  is  sometimes  distilled,  by  which  light  oils,  illuminating 
oils,  heavy  oil,  and  paraffine  are  obtained.  Or  it  is  refined  by  treat- 
ing with  sulphuric  acid  and  caustic  soda,  followed  by  a  charcoal  or 
bone-black  filtration.  The  product,  called  ceresine,  melts  at  61°  to 
78°  C.*  and  is  similar  to  beeswax.  It  appears  to  belong  among  the 
olefines,  having  the  general  formula  CnH2n.  Its  color  ranges  from 
pale  yellow  to  white,  according  to  the  degree  of  refining. 

It  is  used  as  candle  stock ;  for  preparing  insulating  compounds 
for  electrical  work;  in  making  a  black  dressing  for  shoes  and  har- 
ness leather,  and  to  adulterate  beeswax. 

ASPHALT 

Asphalt  or  mineral  pitch  is  probably  an  oxidized  residue  from  the 
evaporation  of  petroleum.  This  name  is  usually  applied  only  to  the 
solid  bitumens,  the  semi-solid  or  liquid  bitumen  being  called  maltha, 
or  mineral  tar.  Asphalt  generally  contains  sulphur  and  nitrogenous 
bodies,  but  is  chiefly  composed  of  hydrocarbons.  The  crude  material 
consists  of  two  chief  ingredients,  that  soluble  in  petroleum  spirit, 
called  pctrolene,  and  an  insoluble  black  substance  called  asphaltene. 
Asphalt  occurs  in  large  quantities  in  and  near  the  "  pitch  lake  " 
on  the  island  of  Trinidad ;  also  in  Cuba,  Venezuela,  California,  Utah, 
Texas,  Canada,  and  in  many  European  countries.  The  Utah  deposit 
is  particularly  pure  (gilsonite)  and  is  much  used  for  black  varnish  and 
for  insulating  material.  It  is  also  much  used  as  a  protective  paint  for 
the  interior  of  chlorine  stills,  bleaching  powder  chambers,  acid  tanks, 
and  for  waterproofing  purposes.  Its  chief  use  is  for  sidewalks  and  pave- 
ments, for  which  it  is  mixed  with  pulverized  limestone  or  with  the 
natural  asphalt  rock.  The  latter  falls  to  a  loose  granular  mass  when 
heated  until  the  asphalt  softens,  and  is  then  rolled  and  stamped  into 
place  with  hot  irons.  A  certain  proportion  of  purer  asphalt,  or  of  the 
heavy  petroleum  oils,  is  often  added  to  the  mixture  to  render  it  more 
plastic. 

Crude  asphalt  contains  much  moisture  and  mineral  matter.  It 
is  refined  by  heating  until  melted,  whereby  the  moisture  is  expelled 
and  some  of  the  mineral  matter  separates  by  subsidence.  Two  vari- 
eties of  Trinidad  asphalt  are  in  commerce,  —  "  lake  pitch  "  and  "  land 
pitch."  The  latter  is  harder,  and  has  the  higher  melting  point.  As- 
phalt is  soluble  in  carbon  disulphide,  acetone,  and  benzene,  but  not 
in  alcohol  nor  water.  When  heated,  it  softens  at  from  80°  to  100°  C. 

*  Redwood. 


348  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


REFERENCES 

Petroleum  Distillation.     A.  N.  Leet,  New  York,  1884. 

Report  on  Petroleum  ;  U.  S.  Census,  1880.     S.  F.  Peckham,  Washington, 

1885. 

Das  Erdol  von  Baku.     C.  Engler,  Stuttgart,  1887.     (Enke.) 
A  Practical  Treatise  on  Petroleum.     Benj.  J.  Crew,  Phila.,  1887.     (Baird 

&Co.) 

Die  deutsche  Erdole.     C.  Engler,  Stuttgart,  1888.     (Enke.) 
Le  Petrole.     Henry  Deutsch,  Paris. 

Das  Erdol  und  seine  Verarbeitung.     A.  Veith,  Braunschweig,  1892. 
Petroleum  ;   Its  History,  Origin,  etc.     W.  T.  Brannt,  Phila.,  1895.     (Baird 

&  Co.) 

Die  Fabrication  der  Mineralole.     W.  Scheithauer,  Braunschweig,  1895. 
Treatise  on  Petroleum,  2  vols.     B.  Redwood  and  G.  T.  Holloway,  London, 

1896.     (Griffin  &  Co.) 

U.  S.  Geological  Survey,  8th  report.     (Formation  of  Petroleum.) 
Report  of  Experts  on  Asphalt  Paving.     Dept.  Public  Works,  Philadelphia, 

1894. 

L'Asphalte.     Leon  Malo,  Paris,  1888.     (Baudry  et  Cie.) 
Mineral   Oils  and   their  By-Products.     I.   I.   Redwood,   London,   1897. 

(Spon.) 

On  the  Nature  and  Origin  of  Asphalt.     C.  Richardson,  New  York,  1898. 
Der  Asphalt  und  seine  Anwendung.     W.  Jeep,  Leipzig,  1899. 
The  Oil  Fields  of  Russia.     A.  Beeby  Thompson,  London,  1904. 
Das  Erdol,   seine  Verarbeitung  und  Vervendung.     R.   Kissling,   Halle, 

a.  S.,  1908. 

Lubricating  Oils,  Fats  and  Greases.     G.  H.  Hurst,  3rd  ed.,  London,  1911. 
A  Short  Handbook  of  Oil  Analysis.     A.  H.  Gill,  6th  ed.,  Philadelphia, 

1911. 
American  Chemical  Journal,  16,  406.     The  Origin  of  Petroleum  and  of 

Natural  Gas.     F.  C.  Phillips. 
Proceedings  of  the  American  Academy  of  Arts  and  Sciences,  Vol.  32. 

Investigations  on  American  Petroleum.     Charles  F.  Mabery. 
Proceedings  of  the  American  Philosophical  Society,  Vol.  36,  No.  154. 

Origin  and  Chemical  Composition  of  Petroleum.     S.  P.  Sadtler. 
Journal  of  the  Society  of  Chemical  Industry :  — 

1890,  359,  The  Oil  Fields  of  India,  Burmah,  etc.     B.  Redwood. 

1894,  719,  Removal  of  Sulphur  from  Petroleum. 

1894,  790,  Origin  of  Petroleum.     F.  C.  Phillips. 

1894,  794,  Present  State  of  the  Petroleum  Industry. 

1894,  872,  American  and  Russian  Petroleums. 
Journal  of  the  Association  of  Engineering  Societies :  — 

1894,  On  the  Composition  of  the  Ohio  and  Canadian  Sulphur  Petro- 
leum.    C.  F,  Mabery. 
Mineral  Resources  of  the  United  States,  1882  +. 


VEGETABLE   AND   ANIMAL   OILS,   FATS,   AND 

WAXES 

These  oils  are  usually  called  "  fatty  "  oils,  to  distinguish  them 
from  the  mineral  and  essential  oils.  They  are  very  widely  dissemi- 
nated in  nature,  both  in  plants  and  in  animals,  and  often  form  a 
large  percentage  of  the  weight  of  the  substance  in  which  they  are 
found.  They  differ  from  the  mineral  oils  in  their  chemical  composi- 
tion, being  compounds  of  organic  acids,  with  bodies  belonging  to  the 
group  called  alcohols,  i.e.  they  are  esters  or  compound  ethers  of  the 
organic  acids.  In  the  majority  of  cases,  the  alcohol  from  which 
these  esters  are  derived  is  glycerine,  or  glycerol,  C3H5(OH)3,  a  tri- 
atomic  alcohol ;  but  occasionally,  e.g.  in  the  waxes,  a  monatomic 
alcohol  is  the  base.  The  ethers  formed  from  glycerine  with  the  fatty 
acids  are  called  glycerides,  a  name  which  is  sometimes  applied  to  the 
oils  also.  The  glycerine  radical  C3H5  is  called  glyceryl. 

The  acids  most  commonly  found  in  these  glycerides  are  shown  in 
the  following  tables  :  — 

SATURATED   ACIDS.     (ACETIC    SERIES.) 


ACID. 

FORMULA. 

MELTING 
POINT. 

BOILING  POINT. 

SPECIFIC 
GRAVITY. 

Butyric     .     . 

C4H802 

-    3° 

163°  C. 

0.958 

Caproic     .     . 

C6H12O2 

-    1.5° 

205° 

0.929 

Caprylic   .     . 

GgHieC^ 

+  15° 

236° 

0.935 

Capric      .  ,  ." 

CioH2()O2 

+  30° 

269° 

0.930 

Laurie       .     . 

Cj2H.24O2 

+  43.5° 

225° 

at  100  mm.  pressure. 

Mvristic  .     . 

Ci4H28O2 

+  54° 

250° 

at  100  mm.  pressure. 

Palmitic    . 

CieH32O2 

+  62° 

271.5° 

at  100  mm.  pressure. 

Stearic      .     . 

CigHseC^ 

+  70.9° 

291° 

at  100  mm.  pressure. 

Arachidic 

C2()H4oO2 

+  75° 

Carnabuic     . 

C24H4sO2 

+  72.5° 

C  erotic 

C27H54O2 

+  78° 

UNSATURATED   ACIDS.     (ACRYLIC    SERIES.) 


ACID. 

FORMULA. 

MELTING  POINT. 

BOILING  POINT. 

Acrylic      ...... 

C3H4O2 

8°  C. 

140°  C. 

Crotonic    .     .     .     .     .     . 

C4H6O2 

72° 

180° 

Hypogaeic  j 

Ci6H30O2 

{33° 

Physetoleic  j 
Oleic     .     .     .  \.     .    V    . 

[30° 
14° 

Erucic  1 

{34° 

Brassic]               '     *     " 

(60° 

349 


350  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

UNSATURATED   ACIDS.     (PROPIOLIC    SERIES.) 


ACID. 

FORMULA. 

MELTING  POINT. 

SPECIFIC  GRAVITY. 

Linoleic      .... 
Linolenic    .... 
Ricinoleic   .... 

CisHsaOa 

Ci8H3oO2 
CigH^Os 

Liquid  at  -18°  C. 
-10°  C. 

0.940 

The  acids  containing  ten  or  fewer  carbon  atoms  in  the  molecule 
may  be  distilled  under  ordinary  atmospheric  pressure  without  de- 
composition ;  they  are  called  volatile  fatty  acids.  The  others  given 
in  the  tables  are  called  non-volatile  acids;  some  of  them  may  be 
distilled  undecomposed  under  reduced  pressure  or  by  superheated 
steam. 

With  the  exception  of  a  few  of  the  less  common  oils  and  waxes, 
only  acids  having  an  even  number  of  carbon  atoms  in  the  molecule 
occur  in  the  fatty  oils.  The  glycerides  composing  the  greater  part 
of  the  important  commercial  fats  are  those  of  butyric,  lauric,  pal- 
mitic, stearic,  oleic,  linoleic,  and  ricinoleic  acids ;  to  a  less  extent 
occur  the  esters  of  caproic,  caprylic,  crotonic,  and  myristic  acids. 
The  fats  are  always  mixtures  of  several  glycerides,  and  the  propor- 
tion in  which  these  are  present  determines  the  nature  of  the  fat, 
whether  hard,  soft,  or  liquid ;  while  certain  peculiar  properties  of 
some  fats  are  due  to  the  presence  of  one  or  two  particular  glycerides. 

The  glycerides  of  palmitic  and  stearic  acids  are  white  crystalline 
solids,  melting  at  61°  and  72°  C.  respectively;  that  of  oleic  acid  is 
liquid  at  ordinary  temperature. 

The  fatty  acids  are  monobasic,  and  glycerine  being  a  triatomic 
alcohol,  the  glycerides  are  composed  of  three  acid  radicals  combined 
with  one  alcohol  rest;  thus  the  glyceride  of  palmitic  acid  has  the 
formula  (CieHsiC^s  =  C3H5,  and  is  called  tripalmitin,  or,  more  often, 
simply  palmitin.  The  glyceride  of  stearic  acid  is  (Ci8H35O2)3  =  C3H5, 
called  tristearin  or  stearin.  That  of  oleic  acid  is  (CigHaaC^s  EE  CsHs, 
called  triolein  or  olein. 

The  fats  and  oils  are  lighter  than  water.  They  cannot  be  boiled 
or  distilled,  even  under  reduced  pressure,  for  when  heated  much 
above  their  melting  point  they  decompose.  Among  other  products 
of  decomposition  is  a  substance  called  acrolein  CH2  =  CH  —  CHO. 
This  is  a  low  boiling  liquid,  having  a  very  disagreeable  odor,  and 
whose  vapors  are  very  irritating  to  the  eyes. 

Fresh  fats  are  nearly  odorless  and  of  neutral  reaction,  but  when 


VEGETABLE  AND  ANIMAL   OILS,   FATS,  AND  WAXES     351 

exposed  to  the  air  for  some  time  many  of  them  undergo  a  change  by 
which  the  glycerides  are  decomposed  and  the  fatty  acids  set  free, 
while  glycerine  is  formed  and  usually  further  decomposed  at  once. 
This  breaking  up  of  an  organic  ester  into  free  acid  and  an  alcohol  is 
called  hydrolysis,  since  the  elements  of  water  are  taken  up  by  the 
acid  and  alcohol.  Thus  if  R  represent  the  acid  radical,  hydrolysis 
of  a  fat  may  be  represented  by  the  general  equation  :  — 

CH2OR  CH2OH 


:HOR  +  3  H  •  OH  =  CHOH  +  3  H  -  OR. 

I  I 

CH2OR  CH2OH 

This  change  is  often  brought  about  by  the  fermentation  or  putre- 
faction of  other  substances  of  a  gelatinous  or  albuminous  character 
present  in  the  oil,  and  is  accompanied  by  numerous  secondary  re- 
actions, which  produce  bodies  of  a  very  disagreeable  odor  and  taste. 
The  oil  is  then  said  to  be  "  rancid." 

Hydrolysis  may  be  readily  brought  about  by  chemical  means,  and 
is  then  called  "  saponification  "  ;  in  this  case  the  reaction  is  much  more 
complete,  and  these  secondary  reactions  do  not  occur.  The  process  is 
employed  in  soap  and  glycerine  manufacture,  as  will  appear  later. 

Certain  oils  are  oxidized  when  exposed  to  the  air,  and  are  con- 
verted into  thick  gummy  or  resinous  masses,  or  in  thin  layers  form 
dry,  hard,  transparent,  or  translucent  films.  This  change  is  called 
"  drying,"  and  is  most  noticeable  in  oils  containing  the  glycerides  of 
linoleic,  linolenic,  and  ricinoleic  acids,  which,  being  un saturated, 
oxidize  very  readily. 

The  unsaturated  compounds  of  the  fatty  acid  series  unite  directly 
with  hydrogen  in  the  presence  of  suitable  catalyzers,  to  form  saturated 
bodies ;  *  thus  oleic  acid  (CigH^Cy  is  converted  to  stearic  acid 
(CigHaeC^),  and  olein  yields  stearin,  which  have  greater  commercial 
value,  owing  to  their  higher  melting  points.  Platinum,  palladium, 
copper,  nickel,  and  other  metals  have  been  tried  as  catalyzers,  but 
nickel  is  found  most  suitable,  since  it  is  highly  active  and  of  moderate 
cost.  The  nickel  is  used  as  a  finely  divided,  metallic  deposit  upon 
some  kind  of  inert  support,  or  carrier,  as  pumice-stone,  kieselguhr, 
asbestos,  or  charcoal. 

A  solution  of  nickel  salt  is  mixed  with  the  pulverized  carrier,  an 
alkali  added  to  precipitate  the  hydroxide,  and  the  mass  after  filter- 
pressing  is  washed  free  from  soluble  matter,  and  dried.  The  product 

*  Jour.  Soc.  Chem.  Ind.,  1912,  1155. 


352 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


is  ground  fine,  and  the  nickel  reduced  by  heating  to  300°  C.,  in  an 
atmosphere  of  hydrogen ;  precautions  to  prevent  feoxidation  during 
cooling  and  subsequent  handling  must  be  taken. 

The  reduced  nickel  catalyzer  is  then  mixed  with  the  oil  and  intro- 
duced into  a  vessel  where  it  can  be  treated  at  about  175°  to  200°  C., 
with  hydrogen  gas,  under  pressures  ranging  from  atmospheric  up  to 
25  pounds  per  square  inch.  The  operation  is  continued  until  test- 
portions  show  that  the  fat  has  acquired  a  sufficiently  high  melting 
point,  when  the  hot  oil  is  filter-pressed  to  remove  the  catalyzer  and 
carrier,  and  then  cooled.  Oils  containing  linoleic,  linolenic,  and  other 
less  saturated  bodies  are  also  converted  to  hard  fats  by  this  treatment, 
but  require  more  prolonged  exposure  to  the  hydrogen. 

These  hardened  fats  now  find  extensive  use  in  the  preparation  of 
lard  substitutes  and  other  food  products,  and  for  soaps,  and  in  mak- 
ing lubricants.  "  Thickened  "  cotton -seed,  peanut,  sesame,  or  other 
edible  oils  have  largely  replaced  the  oleo-stearin  from  tallow  in  lard 
compounds. 

Oils  and  fats  are  found  in  every  part  of  plants  and  animals,  certain 
parts  being  richer  than  others.  In  plants,  the  seeds  or  fruit  generally 
contain  the  most  oil,  but  the  quantity  varies,  even  in  the  same  variety 
of  plant,  according  to  the  soil,  cultivation,  climate,  and  the  maturity 
of  the  fruit.  Usually  it  is  in  inverse  ratio  to  the  amount  of  sugar  and 

starch  present.  In  animals,  most  of 
the  fat  is  found  in  the  abdominal 
cavity,  surrounding  the  kidneys,  or 
in  a  layer  just  beneath  the  skin. 
The  latter  is  especially  true  in  the 
case  of  marine  animals  (whales,  etc.) 
and  those  living  in  cold  climates. 

.The  vegetable  oils  are  obtained 
by  crushing  or  grinding  that  part 
of  the  plant  richest  in  oil,  and  then 
pressing  the  crushed  material,  or  ex- 
tracting it  with  some  solvent,  such 
as  benzine  or  carbon  disulphide. 
Mills  for  crushing  olives  are  of  great 
antiquity,  the  oldest  form  being 
light  edge-runners  of  wood  or  stone, 
FlG-  107-  that  did  not  break  the  kernels. 

Heavy  edge-runners  of  stone  or  iron  (Fig.  107)  are  used  at  the  present 
time,  but  steel  rolls  and  buhr-stone  mills  are  more  generally  em- 


VEGETABLE   AND  ANIMAL  OILS,   FATS,   AND  WAXES     353 


ployed.  The  edge-rtinner  consists  of  two  heavy  rollers  (A,  A),  fixed 
on  a  common  axle  (B),  and  travelling  in  a  circle  around  a  vertical 
shaft  (C).  The  rollers  rest  on  a  solid  stone  or  metal  bed  (D),  on 
which  the  material  to  be  ground  is  spread.  Scrapers  (E)  are  fixed  on 
the  shaft  so  that  they  bring  the  material  directly  into  the  path  of  the 
rollers. 

The  ground  pulp  is  pressed  in  strong  canvas  or  camel's-hair  cloths. 
Sometimes  part  of  the  oil  is  -expressed  cold,  and  the  meal  is  then 
heated  and  pressed  a  second  time  while  hot.  Cold-pressed  oils  are 
of  lighter  color  and  of  better  quality,  but  hot  pressing  gives  a  larger 
yield.  Wedge-presses  and  screw- 
presses  were  used  in  ancient  times, 
but  the  invention  of  the  hydraulic 
press  by  Bramah  in  1795  revolu- 
tionized oil  pressing.  Knuckle-joint 
and  eccentric  presses  are  later  in- 
ventions, but  are  not  so  extensively 
used. 

The  hydraulic  press  (Fig.  108) 
consists  of  a  large  piston  or  ram  (R), 
which  is  forced  out  of  its  cylinder 
(C)  by  the  hydrostatic  pressure  of  a 
liquid  pumped  into  the  cylinder  in  a 
small  stream.  The  bags  of  pulp  (B) 
are  placed  between  the  ram  and  a 
fixed  top  plate  (P),  and  the  oil  ex- 
pressed is  caught  in  troughs  placed 
around  the  ram  head. 

In  1850  Jesse  Fisher  of  Birmingham,  England,  invented  the  extrac- 
tion process,  using  a  volatile  solvent  such  as  carbon  disulphide,  or 
better,  petroleum  naphtha.  The  solvent  is  pumped  into  a  closed 
vessel  containing  the  pulp.  After  extraction,  the  solution  of  oil  in 
the  solvent  is  drawn  off  and  the  latter  recovered  by  distilling  it  off 
from  the  oil.  This  method  gives  a  larger  yield  of  oil,  comparatively 
free  from  gelatinous  matter,  but  some  resins  and  coloring  matter 
may  be  dissolved,  thus  contaminating  it,  and  up  to  the  present  time 
edible  oils  are  not  prepared  by  this  process,  owing  to  the  persistence 
of  the  odor  and  taste  of  the  solvent.  A  complicated  and  expen- 
sive recovery  plant  which  is  also  costly  to  operate  is  required. 
Moreover,  if  the  extraction  is  carried  too  far,  the  residue  of  crushed 
seed  pulp  has  less  value  as  animal  food  and  is  chiefly  used  as  fertilizer 

2A 


FIG.  108. 


354 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


or  fuel.  Pressing  involves  less  fire  risk  and  yields  a  lighter  colored 
oil,  especially  if  done  cold,  while  the  press-cake  from  many  vegetable 
oils  has  a  high  value  as  cattle  food,  owing  to  the  oil  and  proteids 
remaining  in  it. 

Animal  oils  are  contained  in  cells  composed  of  membranous 
tissue  which  putrefies  soon  after  the  animal  is  killed,  causing  the  fat 
to  become  rancid  and  have  a  bad  odor.  Consequently  it  must  be 
rendered  immediately.  These  oils  are  obtained  by:  (a)  melting, 
"  trying  out,"  or  rendering  in  open  kettles.  The  fat  is  chopped  into 
small  bits  and  heated  over  a  fire  with  a  very  little  water.  The  tissue 

shrivels  together  forming  "  cracklings," 
which  float  on  the  oil  and  are  removed 
by  straining  and  are  pressed  to  obtain 
all  the  oil.  Much  care  is  required  to 
prevent  overheating,  and  this  process 
has  been  generally  abandoned  in  favor 
of  steam  rendering  (see  below) ;  (6)  by 
boiling  with  water  to  which  sulphuric 
acid  is  sometimes  added  to  decompose 
the  cell  walls,  thus  liberating  the  oil; 
(c)  by  heating  with  direct  steam  under 
pressure  in  large  digesters  or  autoclaves 
(Fig.  109),  breaking  down  the  cell  walls. 
The  fat  is  introduced  through  the  man- 
hole (B)  which  is  closed  when  the  di-* 
gester  is  nearly  filled  to  the  top,  and 
steam  at  about  50  pounds  pressure  is 
admitted  by  the  pipe  (C)  entering  near 
the  bottom.  Before  closing  the  digester,  the  fat  is  sometimes  washed 
by  flushing  with  water  which  runs  off  by  the  cocks  (D)  and  (E). 
The  foul-smelling  gases  given  off  during  the  rendering  are  conducted 
away  by  the  pipe  (H),  and  after  cooling  to  condense  steam  they  are 
discharged  into  the  chimney  or  into  a  closed  sewer.  After  several 
hours  heating,  the  steam  is  cut  off,  the  pressure  relieved,  and  the 
digester  allowed  to  remain  quiet  until  the  oil  has  risen  to  the  top, 
leaving  the  cracklings  and  condensed  water  in  the  bottom  of  the 
tank.  The  progress  of  the  separation  may  be  followed  by  trials  at 
the  test-cocks  (F,  F).  The  water  is  then  drawn  off  through  (E),  until 
the  oil  reaches  the  level  of  (G),  through  which  it  is  then  drawn 
off.  The  cracklings  are  discharged  by  dropping  the  lower  manhole 
cover  (J). 


FIG.  109. 


VEGETABLE   AND   ANIMAL   OILS,   FATS,   AND  WAXES      355 

In  testing  fatty  oils,  certain  distinguishing  properties  and  reactions 
are  sought.  The  specific  gravity  is  an  important  indication  as  to  the 
purity  of  the  sample.  It  is  determined  by  the  Westphal  balance,  Sprengel 
tube,  or  specific  gravity  bottle. 

The  saponification  value  *  represents  the  number  of  milligrams  of 
potassium  hydroxide  needed  to  saponify  one  gram  of  the  oil.  It  is  de- 
termined by  saponifying  one  or  two  grams  of  the  oil  with  25  cubic  centi- 
meters of  —  alcoholic  potassium  hydroxide  and  titrating  the  excess  alkali 

N 
with  —  hydrochloric  acid,  using  phenolphthalein  as  indicator. 

The  iodine  (or  bromine)  value  *  represents  the  percentage  of  iodine 
(or  bromine)  absorbed  by  the  oil,  forming  addition,  or  to  a  smaller  extent, 
substitution  products.  The  saturated  fatty  acids  and  their  glycerides 
do  not  combine  with  the  halogens  to  any  appreciable  extent ;  but  those  of 
the  oleic  or  ricinoleic  series  combine  with  two  atoms  of  iodine  (or  bromine) ; 
those  of  the  linoleic  unite  with  four,  and  of  the  linolenic  with  six,  atoms 
of  the  halogen.  Thus  the  determination  of  this  value  affords  a  method 
of  determining  the  percentage  of  unsaturated  fatty  acids  (or  glycerides) 
present  in  the  oil.  The  weighed  amount  of  oil  (0.2  gram)  dissolved  in 
10  cc.  of  chloroform  is  mixed  with  30  cc.  of  a  standard  solution  of  iodine 
in  mercuric  chloride  and  shaken  occasionally  during  fifteen  minutes ; 
15  cc.  of  potassium  iodide  solution  is  added  and  the  excess  iodine  titrated 

with  —  sodium  thiosulphate.  f     The  number  of  cc.  of  thiosulphate  used, 

multiplied  by  its  value  in  terms  of  iodine,  gives  the  number  of  grams  of 
iodine  not  absorbed  by  the  oil ;  the  difference  between  this  quantity  and 
the  amount  of  iodine  added  to  the  oil  gives  the  weight  absorbed  by  the 
oil ;  this  divided  by  the  weight  of  oil  used  and  multiplied  by  100  gives  the 
iodine  value. 

The  Maumene  testj  shows  the  amount  of  heat  developed  when  oil  is 
mixed  with  sulphuric  acid.  Fifty  grams  of  the  oil  are  treated  with  ten 
cubic  centimeters  of  strong  acid  under  exact  conditions,  and  the  "  rise 
in  temperature  "  observed. 

The  elaidin  test  depends  upon  the  fact  that  nitrous  anhydride  (N203), 
when  brought  into  contact  with  olein,  converts  it  into  the  isomeric  solid 
elaidin,  but  the  glycerides  of  linoleic,  linolenic,  and  isolinolenic  acids  are 
not  affected  by  this  treatment.  Thus  the  non-drying  oils  become  solid, 
while  the  semi-drying  and  drying  oils  remain  liquid,  or  at  most,  become 
buttery.  Five  grams  of  oil  are  mixed  with  seven  grams  of  nitric  acid 
(1.34  sp.  gr.),  about  one  gram  of  copper  wire  added,  and  the  glass  placed 
in  cold  water  (15°  C.)  and  the  oil  well  stirred.  After  standing  two  or  three 
hours  the  solidity  of  the  elaidin  cake  is  examined. 

*  Oils,  Fats,  and  Waxes.     Benedikt-Lewkowitsch. 

t  Oil  Analysis.     A.  H.  Gill. 

J  Compte  Rendu,  35  (1852),  572. 


356  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

For  convenience  in  study,  the  fatty  oils  are  generally  classified 
according  to  certain  similarities  in  their  properties  and  sources.  A 
convenient  classification  is  as  follows  * :  — 

Oils  and  Fats.     Glycerides. 
OILS  OR  LIQUID  FATS 
Vegetable  Oils. 

Drying  Oils.     (1) 
Semi-Drying  Oils.     (2) 
Non-Drying  Oils.     (3) 

Animal  Oils. 

Fish  Oils.     (4) 


Marine 


Liver  Oils.     (5) 


Blubber  Oils.     (6) 
Terrestrial.     (7) 

SOLID  FATS. 

Vegetable  Fats.     (8) 
Animal  Fats.     (9) 

Waxes.     Non-Glycerides. 

LIQUID  WAXES.     (10) 

SOLID  WAXES. 

Animal  Waxes.     (11) 
Vegetable  Waxes.     (12) 

*  Oils,  Fats,  and  Waxes.     Benedikt-Lewkowitsch. 


OILS  AND  FATS 

(1)   VEGETABLE  DRYING  OILS 

Linseed  oil  is  derived  from  the  seeds  of  the  flax  plant,  Linum 
usitatissimum,  L.,  which  is  extensively  cultivated  in  northern  Europe, 
Italy,  Turkey  (near  the  Black  Sea),  India,  Argentina,  and  in  the 
United  States.  When  the  plants  are  raised  for  their  fibre  (p.  490), 
they  are  pulled  up  before  the  seeds  are  ripe ;  such  seed  must  be  aged 
several  months  before  pressing,  but  the  best  oil  is  obtained  from  ripe 
seed.  The  yield  is  from  25  to  32  per  cent,  according  as  the  seeds 
are  pressed  or  extracted.  The  cold-pressed  cake  is  often  heated 
and  pressed  again.  Cold-pressed  oil  is  a  clear  golden  yellow,  while 
the  hot-pressed  product  is  amber  or  brown.  The  latter  may  be 
"  bleached  "  by  treating  with  a  solution  of  ferrous  sulphate  and  ex- 
posing it  to  the  sunlight.  The  crude  oil  is  stored  until  the  muci- 
laginous matter  and  water  settle ;  the  product  is  called  "  tanked 
oil."  Or  the  crude  oil  is  refined  by  agitation  with  sulphuric  acid, 
followed  by  washing  with  water.  The  "tanked"  or  purified  product 
is  called  "raw  oil." 

Press-cake  from  raw  oil  is  one  of  the  most  valuable  cattle  foods. 

Linseed  oil  is  the  most  important  of  the  drying  oils.  It  contains  * 
about  65  per  cent  of  the  glycerides  of  isolinolenic  acid,  CisH-soOz,  and 
15  per  cent  each  of  the  glycerides  of  linoleic,  CisH^C^,  and  linolenic, 
CisHsoC^,  acids  and  5  per  cent  of  olein.  These  glycerides  absorb 
oxygen,  and  are  converted  into  an  elastic  mass,  linoxyn,  of  doubtful 
composition,  which  has  been  thought  to  be  insoluble  anhydrides  of  the 
acids.  The  oil  becomes  thicker  and  darker  colored,  and,  when  in 
thin  films,  forms  a  dry,  hard  varnish.  This  drying  may  be  hastened 
by  the  so-called  "  boiling  "  of  the  raw  oil.  The  latter  is  heated  with 
certain  salts  (such  as  litharge,  lead  acetate,  or  the  peroxide  or  borate 
of  manganese),  called  "  driers."  A  slight  decompositon  of  the  glyc- 
erides occurs,  and  some  acrolein  is  set  free ;  also  a  slight  polymeriza- 
tion takes  place.  Possibly  the  driers  form  metallic  salts  with  the 
fatty  acids  to  a  small  extent,  the  glycerides  being  partly  saponified 
in  the  process ;  the  metallic  salts  remain  dissolved  in  the  oil  and  act 
as  oxygen  carriers  in  the  drying,  when  they  are  exposed  to  the  air. 
The  boiling  is  carried  on  in  open  kettles  heated  by  direct  fire  or  by 

*  K.  Hazura.     Zeit.  fur  angew.  Chem.,  1888,  312. 
357 


358  OUTLINES   OF   INDUSTRIAL  CHEMISTRY 

high-pressure  steam,  and  is  sometimes  aided  by  blowing  air  into  the 
hot  oil.  When  the  latter  has  lost  from  8  to  10  per  cent  of  its  weight, 
the  process  is  stopped.  The  temperature  employed  varies  with  the 
kind  of  drier  used,  being  highest  (250°  C.)  with  litharge;  but  this 
gives  a  dark-colored  product.  The  lower  the  temperature  the  lighter 
colored  the  product,  and  the  longer  the  oil  must  be  heated.  By 
heating  the  oil  for  several  days  with  borate  of  manganese  at  60°  C. 
to  125°  C.,  a  very  light-colored  boiled  oil  is  produced.  All  boiled  oil 
should  stand  several  months,  or  even  a  year,  before  use,  in  order 
that  the  impurities  may  settle.  Very  little  of  the  drier  is  dissolved 
by  the  oil,  and  the  clarified  boiled  oil  is  decanted  from  the  residue. 
It  dries  very  readily,  and  is  much  used  for  paint  mixing.  If  the 
boiling  is  continued  for  ten  or  twelve  hours,  at  a  high  temperature, 
the  oil  becomes  a  thick,  sticky,  viscid  mass,  used  as  the  basis  of 
printers'  ink. 

If  a  small  quantity  of  oil  is  brought  to  a  high  heat  with  the  metal- 
lic salt,  a  dark-colored  liquid  "  drier  "  or  "  japan  "  is  formed,  which 
may  be  mixed  with  a  greater  amount  of  raw  oil  at  a  moderate  tem- 
perature (100°  to  125°  C.).  This  forms  a  so-called  "  bung-hole  " 
boiled  oil,  which  is  lighter  colored  than  if  the  whole  mass  of  oil  had 
been  heated  to  a  high  temperature.  The  product  is  claimed  to  have 
as  good  drying  properties  as  the  genuine  kettle-boiled  oil. 

Several  grades  of  linseed  oil  are  in  the  market,  the  Calcutta  being 
considered  the  best  in  this  country,  while  the  Western  and  La  Plata 
oils  are  often  of  poorer  quality.  In  Europe  the  Baltic  oil  *  is  held  in 
high  esteem,  while  the  Indian  oils  are  regarded  as  low  grade.  Lin- 
seed oil  is  sometimes  adulterated  with  mineral  oil,  or  with  rosin,  corn, 
menhaden,  or  cotton-seed  oil. 

Raw  linseed  oil  has  a  specific  gravity  of  0.9316  to  0.9354 ;  saponi- 
fication  value  of  189  to  195,  and  an  iodine  value  of  170  to  188.  (Boil- 
ing lowers  the  iodine  number.)  It  does  not  yield  solid  elaidin.  It 
is  used  as  a  soap  stock  for  soft  soap,  in  some  kinds  of  paint,  for  varnish 
making,  and  for  rubber  substitute.  Boiled  oil  is  used  for  paint,  for 
printing  inks,  for  oilcloth  making,  and  in  the  preparation  of  linoleum. 
For  this  last,  the  partially  boiled  oil  is  exposed  to  the  air  at  a  moderate 
temperature  (20°  to  22°  C.),  until  oxidized  to  a  translucent  jelly. 
It  is  then  thoroughly  incorporated  with  ground  cork,  and  is  rolled 
into  sheets  and  dried. 

*  Lewkowitsch,  Oils,  Fats,  and  Waxes.  Allen,  Commercial  Organic  Analysis, 
Vol.  II.  Mcllhiney,  Report  upon  Linseed  Oil  and  its  Adulterants,  to  Commissioner 
of  Agriculture  of  New  York  State,  Albany,  1901. 


OILS  AND  FATS  359 

By  the  oxidation  of  certain  oils,  as  in  "  drying,"  considerable 
heat  is  generated,  and  if  they  are  exposed  in  thin  layers,  on  porous, 
inflammable  material  (e.g.  when  absorbed  in  cotton  rags  or  waste), 
spontaneous  combustion  frequently  takes  place.  This  is  particularly 
liable  to  occur  with  linseed  oil ;  it  may  be  prevented  by  the  addition 
of  mineral  oils. 

Hemp  oil  is  obtained  from  the  seeds  of  the  common  hemp,  Can- 
nabis  satim,  L.  The  yield  is  about  30  per  cent.  It  is  a  greenish 
yellow  oil  of  0.925  to  0.930  sp.  gr.  Its  saponification  value  is  190  to 
191.1,  and  its  iodine  value  143  to  148.  It  is  a  poor  drying  oil,  but  is 
used  in  paint  and  as  an  adulterant  for  linseed  oil ;  also  as  stock  for 
soft  soap. 

Soja  (or  soya)  bean  oil,  obtained  from  the  seeds  of  Soja  hispida, 
cultivated  in  China  and  Formosa,  furnishes  an  important  edible  oil, 
and  soap  stock.  Its  sp.  gr.  is  0.9255;  saponification  value,  193.2; 
iodine  number,  137  to  141 ;  Maumene  test,  86  to  87 ;  index  of  refrac- 
tion, 1.4750  at  20°  C.  The  press-cake  is  a  valuable  cattle  food. 

Poppy  oil  is  a  good  drying  oil,  from  the  seeds  of  the  poppy,  Papaver 
somniferum,  L.  The  yield  is  about  45  per  cent  of  a  thin,  yellow, 
odorless  oil  of  0.924  to  0.937  sp.  gr. ;  its  saponification  value  is  190 
to  197;  iodine  value,  134  to  143.  It  is  used  as  a  salad  oil  and  to 
adulterate  olive  oil ;  and  in  the  preparation  of  colors  for  artists'  use. 

Tung  oil,  or  Chinese  wood  oil,  from  the  seeds  of  Aleurites  cordata, 
a  tree  native  to  China  and  Japan,  is  chiefly  used  for  paints,  varnishes, 
and  in  making  oilcloth.  It  is  a  pale  yellow  to  dark  brown  in  color, 
and  dries  rapidly,  forming  a  hard  film.  Its  sp.  gr.  is  0.941  at  15°  C. ; 
saponification  value,  190  to  1Q7 ;  iodine  number,  155  to  170.  It  con- 
tains glycerides  of  oleic  and  elseomargaric  (CigH&C^)  acids. 

Sunflower  oil  is  a  pale  yellow,  palatable,  odorless  oil,  from  the 
seeds  of  the  common  sunflower,  Helianthus  annuus,  L.  The  yield  is 
about  30  per  cent,  and  the  press-cake  is  a  valuable  cattle  food.  The 
oil  contains  the  glycerides  of  oleic,  palmitic,  arachidic,  and  linoleic 
acids.  Its  sp.  gr.  is  0.924  to  0.926 ;  saponification  value,  190  to  194 ; 
iodine  value,  120  to  133.  It  is  used  as  a  soap  stock,  for  wool  oiling, 
and  to  adulterate  olive  oil. 

(2)  VEGETABLE  SEMI-DRYING  OILS 

These  oils  have  an  intermediate  position  between  the  true  drying 
and  the  non-drying  oils,  some  of  them  showing  distinct  drying  proper- 
ties, while  others  do  not,  as  is  indicated  in  their  iodine  values. 


360  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

Corn  oil  or  maize  oil  is  derived  from  the  germ  of  the  common  corn, 
Zea  Mays,  L.  The  germ  (removed  from  the  grain  in  starch  making), 
when  pressed,  yields  a  yellow  oil  of  0.920  to  0.927  sp.  gr.  Its  saponifi- 
cation  value  is  188  to  193  ;  iodine  value,  111  to  123  ;  Maumene  test,  56° 
to  88°  C.  It  is  used  as  an  edible  oil ;  in  making  soap  and  lubricants  ; 
and  for  rubber  substitutes ;  the  press-cake  is  an  excellent  cattle  food. 

Cotton-seed  oil  is  derived  from  the  seeds  of  the  cotton  plant, 
Gossypium  herbaceum,  L.  After  the  husks  are  removed  in  cylinders 
containing  rotary  knives,  the  seeds  are  crushed  in  a  roller  mill. 

The  meal,  heated  in  iron  kettles  at  75°  to  90°  C.,  is  pressed  under 
3000  to  4000  Ibs.  per  square  inch.  The  yield  is  about  18  per  cent. 
The  press-cake  is  a  valuable  cattle  food,  but  is  mixed  before  feeding 
with  two  parts  of  the  seed  hulls,  straw,  or  other  fodder. 

The  crude  oil  is  red  or  reddish  brown  in  color,  and  must  be  re- 
fined for  most  purposes.  After  settling,  it  is  pumped  into  large  iron 
tanks  having  stirring  apparatus,  and  steam  coils  for  heating;  here 
the  heated  oil  is  agitated  for  a  few  minutes  with  a  solution  of  caustic 
soda  of  12°  to  18°  Be.  The  alkali  combines  with  the  free  fatty  acid 
of  the  oil  to  form  a  soap,  insoluble  in  the  oil.  This  soap  is  an  effective 
adsorption  agent  for  the  coloring  and  albuminous  matter,  and  sepa- 
. rates  together  with  the  excess  lye  as  "  foots."  The  agitator  is  then 
stopped,  the  "  foots  "  settle  to  the  bottom,  and  the  clear  oil  is  drawn 
off.  The  amount  of  lye,  temperature  of  the  oil,  and  time  of  agitation 
varies  according  to  the  judgment  of  the  operator.  The  "  foots  "  are 
used  for  soap  stock.  The  clarified  oil  is  still  yellow  and  for  some 
uses  is  further  bleached  by  treatment  with  fuller's  earth,  at  a  tem- 
perature of  about  100°  C.,  and  with  active  stirring  for  a  few  minutes ; 
the  earth  is  then  filtered  out  of  the  oil,  leaving  it  water  white  or  yel- 
lowish color,  according  to  the  quality  of  the  oil.  On  standing  or  by 
chilling  below  12°  C.,  the  palmitin  and  stearin  in  part  crystallize,  and 
may  be  removed  by  pressing.  This  solid  fat,  called  "  cotton-seed 
stearin,"  is  used  in  making  oleomargarine.  The  oil  expressed  is  clear 
and  light-colored,  and  is  extensively  used  as  a  salad  oil  and  to  adulter- 
ate olive  oil.  It  is  also  used  in  the  manufacture  of  "  compound  lard," 
"  cottolene,"  etc.,  for  which  it  is  mixed  with  about  one  and  one-half 
times  its  weight  of  beef  stearin  ;  and  in  butterine  and  oleomargarine, 
to  soften  them  in  cold  weather.  Cotton-seed  oil,  hardened  by  hydro- 
genation,  is  much  used  as  a  substitute  for  lard  as  a  food  product. 

Refined  cotton-seed  oil  has  a  pale  straw  color  and  a  specific  gravity 
of  0.922  to  0.930.  Its  saponification  value  is  191  to  196 ;  iodine  value, 
101  to  116 ;  the  elaidin  test  gives  a  soft  buttery  mass ;  Maumene  test, 


OILS  AND  FATS  361 

70°  to  90°  C.  It  is  usually  free  from  acids  and  has  a  pleasant  taste. 
The  poorer  grades  are  used  for  soap  making.  It  is  not  often  adulterated. 

Sesame  or  Gingili  oil  is  obtained  from  the  seeds  of  an  East  Indian 
plant,  Sesamum  Indicum,  L.,  which  is  also  grown  largely  in  Egypt 
and  Asia  Minor.  The  crushed  seeds  are  first  pressed  cold  and  then 
hot.  The  yield  is  30  to  50  per  cent  of  thin,  yellow,  odorless  oil  of 
pleasant  taste,  which  does  not  become  rancid  on  exposure.  It  con- 
sists of  76  per  cent  olein,  the  remainder  being  glycerides  of  palmitic, 
stearic,  and  myristic  acids.  Its  specific  gravity  is  0.921  to  0.924; 
saponification  value,  190  to  194 ;  it  yields  a  soft  elaidin ;  the  iodine 
number  is  103  to  110 ;  and  the  Maumene  test,  65°  to  68°  C.  The  best 
quality  is  used  as  a  table  oil  or  to  adulterate  olive  oil ;  the  common 
grades  are  good  burning  oils  or  soap  stock. 

Rape-seed  or  colza  oil  is  obtained  from  the  seeds  of  several  vari- 
eties of  Brassica  campestris,  L.  The  seeds  are  crushed  and  heated 
by  steam  before  pressing ;  this  coagulates  the  albumin  and  improves 
the  quality  of  the  oil.  The  yield  is  about  36  per  cent  of  crude  oil 
which  is  refined  by  agitation  with  one  per  cent  of  strong  sulphuric 
acid  and  washing  with  alkali ;  this  removes  traces  of  sulphuric  acid 
and  the  free  fatty  acids  formed  by  its  action.  The  lighter  colored 
and  best  grades  are  generally  called  colza  oil,  rape  oil  being  applied 
to  the  commoner  grades.  Both  contain  the  glycerides  of  oleic,  stearic, 
and  erucic  or  brassic  acids.  The  specific  gravity  ranges  from  0.922 
to  0.930  at  15.5°  C. ;  the  iodine  value  is  101  to  117;  saponification 
value,  191  to  196 ;  by  the  elaidin  test,  solidification  takes  place  very 
slowly,  frequently  requiring  50  to  60  hours,  and  the  elaidin  is  very 
soft;  Maumene  test,  70°  to  90°  C. 

The  purified  colza  oil  is  a  pale  yellow  and  is  odorless ;  it  is  chiefly 
used  as  a  condiment  and  as  a  burning  oil.  It  is  often  adulterated  with 
hemp,  cotton-seed,  or  fish  oils  or  with  rosin  oil.  Common  rape  oil  is 
used  as  a  lubricant,  and  being  very  viscid,  is  frequently  employed  as 
a  standard  for  measuring  viscosity.  When  exposed  to  the  air,  it 
becomes  thick  and  gummy,  but  does  not  really  "  dry." 

Castor  oil  is  obtained  from  the  seeds  of  Ricinus  communis,  L. 
They  are  cold  pressed  for  the  first  grade  of  medicinal  oil,  and  hot 
pressed  for  the  common  qualities,  about  40  per  cent  of  oil  being 
obtained.  It  is  very  viscid,  of  0.960  to  0.970  sp.  gr.,  and  contains 
the  glycerides  of  stearic  and  ricinoleic  acids.  Its  saponification  value 
is  176  to  186;  iodine  value,  81  to  90;  Maumene  test,  47°  C.  It  is 
apt  to  become  rancid,  and  is  soluble  in  alcohol  and  glacial  acetic  acid, 
and  insoluble  in  petroleum  spirit.  Its  purgative  action  is  probably 


362  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

due  to  an  alkaloid  present  in  it.  Large  quantities  are  used  in  making 
"  Turkey-red  oil,"  which  is  prepared  by  treating  the  castor  oil  with 
sulphuric  acid  at  less  than  40°  C.,  and  washing  with  a  strong  brine 
to  remove  the  excess  of  acid.  The  oil  is  decanted  from  the  brine  and 
carefully  neutralized  with  ammonia  or  soda,  by  which  Turkey-red 
oil,  the  alkali  salt  of  ricinoleo-sulphuric  acid,  CisHsspHSOsJOs,  is  formed. 
Oil  thus  prepared  has  largely  replaced  that  made  from  olive  oil  for 
use  in  dyeing  cotton  with  alizarine.  Its  exact  composition  is  as  yet 
uncertain,  various  views  having  been  advanced.* 

Castor  oil  is  also  used  for  making  transparent  soaps  and  common 
soap ;  its  viscosity  being  greater  than  that  of  any  other  oil  at  the  ordi- 
nary temperature,  it  is  largely  used  as  a  lubricant  for  heavy  machinery. 

By  blowing  air  through  hot  cotton-seed,  linseed,  lard,  or  rape  oil, 
it  is  partially  oxidized  and  converted  into  a  thick  viscous  oil  of  very 
high  gravity  (0.942  to  0.970).  Mixed  with  mineral  lubricating  oils, 
these  "  blown  oils  "  are  used  as  substitutes  for  castor  oil  for  heavy 
machinery. 

(3)  VEGETABLE  NON-DRYING  OILS 

These  usually  contain  a  high  percentage  of  olein,  absorb  little  or 
no  oxygen,  and  do  not  dry  in  the  air,  yield  solid  elaidin,  and  have 
lower  iodine  values  than  the  drying  oils. 

Peanut  or  earthnut  oil  is  obtained  from  the  fruit  of  Arachis  hypogcea, 
L.  The  oil  is  a  light  greenish  yellow,  with  a  peculiar  odor  and  taste, 
but  when  refined  the  best  quality  oil  is  colorless  and  has  a  very  faint 
nutty  taste.  It  contains  glycerides  of  arachidic  and  hypogseic  acids, 
besides  olein,  palmitin,  and  others.  Its  specific  gravity  is  0.916  to 
0.922 ;  saponification  value,  190  to  196 ;  and  iodine  value,  85  to  105 ; 
Maumene  test,  45°  to  75°  C.  It  is  employed  as  an  adulterant  for  olive 
oil  (formerly  also  in  lard  oil),  as  a  salad  oil,  in  butterine,  for  oiling 
wool,  and  for  soap  making. 

Olive  oil  is  obtained  from  the  fruit  of  the  olive  tree,  Olea  Europcea, 
L.  Both  the  fruit  pulp  and  the  kernel  contain  oil,  but  the  former 
yields  the  better  quality.  The  fruit  is  crushed  in  mortars  or  edge- 
runners  (care  being  taken  not  to  break  the  kernels)  and  cold  pressed. 
A  small  quantity  of  "  virgin  oil  "  is  thus  obtained,  which  is  used  as  a 
condiment.  The  residue  is  stirred  up  with  hot  water  and  pressed 
harder  than  before;  then  it  is  ground  a  second  time,  crushing  the 

*  J.  Soc.  Chem.  Ind.,  1883,  537.  Liechti  and  Suida.  J.  Soc.  Chem.  Ind.,  1884, 
412.  Mueller  and  Jacobs.  Dingler's  polytechnisches  Jour.,  254,  346.  Schmid. 
J.  Soc.  Dyers  and  Colorists,  1891,  69.  Scheurer-Kestner. 


OILS  AND  FATS  363 

seeds,  stirred  up  with  hot  water,  and  pressed  as  hard  as  possible.  The 
final  press-cake  is  extracted  with  carbon  disulphide,  or  is  put  into  pits 
with  water  and  allowed  to  ferment  for  some  weeks.  The  oil  rises  to 
the  top  and  is  skimmed  off. 

The  several  grades  of  oil  obtained  are  purified  by  heating  to  coagu- 
late the  albuminous  matter,  and  settling.  A  dark-colored,  mucilagi- 
nous substance,  called  "  foots,"  deposits,  and  is  used  for  soap  stock. 
The  lighter  colored  oils  are  used  for  the  table  and  the  others  for  lubri- 
cators, illuminants,  and  soap  stock.  Considerable  of  the  grade  called 
"  Gallipoli  "  is  used  for  making  "  Turkey-red  oil "  and  for  oiling  wool 
after  scouring. 

Olive  oils  vary  in  color  from  pale  yellow  with  a  greenish  tinge 
(due  to  traces  of  chlorophyl)  to  greenish  or  brownish  yellow  in  the 
poorer  qualities.  First-grade  oils  are  odorless  and  palatable,  but 
the  lower  grades  are  strong-smelling  and  usually  have  a  disagreeable 
taste.  On  exposure  to  the  air  olive  oil  is  apt  to  become  rancid. 
The  specific  gravity  varies  from  0.914  to  0.918;  its  saponification 
value  is  185  to  203 ;  iodine  value,  78  to  91.5;  the  elaidin  test  shows 
a  solid  mass  within  two  hours,  which  is  not  displaced  by  inverting 
the  vessel ;  Maumene  test,  41°  to  47°  C.  The  oil  contains  about  72 
per  cent  of  olein  and  linolein,  and  about  28  per  cent  mixed  palmitin 
and  stearin.  Being  very  expensive,  it  is  frequently  adulterated  with 
cotton-seed,  sesame,  or  rape-seed  oil,  while  poppy,  lard,  and  peanut 
oils  are  less  commonly  used. 

MARINE   ANIMAL   OILS 

These  oils  are  glycerides,  and  are  liquid  at  ordinary  temperatures. 
They  absorb  oxygen,  do  not  yield  solid  elaidin,  and  have  high  iodine 
values.  The  varieties  of  sperm  oil  do  not  belong  with  this  group, 
since  they  are  liquid  waxes,  although  obtained  from  blubber. 

(4)  FISH  OILS 

Fish  oils  are  obtained  by  rendering  and  pressing  the  entire  body 
of  the  fish.  The  press-cake,  consisting  of  the  scales,  meat,  and  bones, 
is  ground  and  utilized  as  "  fish  scrap  "  (p.  166),  for  fertilizer  or  for 
feeding  swine. 

Menhaden  or  pogy  oil,  derived  from  a  small  fish,  Alosa  Menhaden, 
is  brownish  color,  has  a  fishy  odor,  and  dries  in  the  air.  Its  specific 
gravity  is  0.927  to  0.933 ;  saponification  value,  189  to  192 ;  iodine 
value,  148  to  160 ;  Maumene  test,  123°  to  128°  C.  It  is  much  used 


364  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

in  currying  (p.  579) ;  to  adulterate  whale  oils  and  linseed  oil  and  as  a 
substitute  for  them.     It  is  itself  adulterated  with  mineral  oils. 


(5)  LIVER  OILS 

These  oils  contain  cholesterol  and  other  biliary  ingredients  which 
are  unsaponifiable. ' 

Cod-liver  oil  is  obtained  from  the  liver  of  the  codfish,  Gadus 
morrhua.  The  livers  are  rendered  by  steam  heat,  and  the  oil  sepa- 
rated, is  chilled  until  the  stearin  solidifies,  when  it  is  pressed  and  the 
clear  oil  collected.  Three  grades  are  made,  —  pale,  light  brown,  and 
dark  brown.  The  pale  oil,  used  in  medicine,  is  limpid,  light  yellow, 
having  little  taste  or  smell ;  its  value  here  may  be  due  to  traces  of 
biliary  substances,  making  it  readily  digested  and  assimilated.  The 
darker,  less  pure  grades  are  used  for  leather  dressing.  The  oil  con- 
tains glycerides  of  oleic,  myristic,  palmitic,  and  stearic  acids,  some 
volatile  fatty  acids,  and  cholesterol ;  also  traces  of  iodine  and  phos- 
phorus. The  specific  gravity  is  0.922  to  0.930  at  15°  C. ;  saponifica- 
tion  value,  182  to  189  ;  iodine  value,  141  to  159  ;  Maumene  test,  102° 
to  113°  C.  It  is  often  adulterated  with  shark-liver  oil,  seal  oil,  and 
other  fish  oils. 

Shark-liver  oil  is  chiefly  obtained  from  the  livers  of  the  sunfish, 
Squalus  maximus.  Its  specific  gravity  is  0.911  to  0.928.  It  is  a  clear 
yellow  oil,  containing  a  large  amount  of  cholesterol,  and  is  mostly 
used  for  leather  dressing  and  for  adulterating  cod-liver  oil. 

(6)  BLUBBER  OILS 

Whale  oil  or  train  oil  is  obtained  from  the  blubber  of  the  Green- 
land or  "  right  "  whale,  Balcena  mysticetus,  and  other  animals  of  the 
whale  tribe.  By  boiling  the  blubber  in  water,  the  oil  rises  to  the 
surface  and  is  skimmed  off.  It  is  yellowish  brown  in  color  and  has 
a  strong  fishy  odor.  Its  composition  is  variable  and  but  little  is 
known  about  it ;  glycerides  of  some  of  the  lower  members  of  the  acetic 
series  are  often  present.  The  glyceride  of  valeric  acid,  C5HioO2,  is 
characteristic  of  some  whale  oils.  The  specific  gravity  is  0.925  to 
0.930 ;  saponification  value,  188  to  193  ;  iodine  value,  120 ;  Maumene 
test,  85°  to  91°  C.  Some  varieties  dry  on  exposure  to  the  air.  Whale 
oil  is  used  for  leather  dressing,  in  tempering  steel,  and  as  an  illuminat- 
ing oil. 

Porpoise  oil,  derived  from  the  porpoise,  Phoccena  brachycium,  is 
very  similar  to  whale  oil,  and  is  obtained  in  the  same  way.  Its  den- 


OILS  AND   FATS  365 

sity  is  0.920  to  0.930;  saponification  value,  216;  it  yields  a  small 
amount  of  elaidin.  The  best  grades  (jaw  oil)  are  used  for  lubricating 
clocks  and  watches,  the  commoner  qualities  for  soap  stock,  for  leather 
dressing,  and  as  illuminating  oil. 

Blackfish  oil  is  obtained  from  the  blubber  of  the  blackfish,  Globi- 
cephalus  melas.  It  is  a  pale  yellow  oil,  which  separates  spermaceti 
(cetyl  palmitate)  on  standing.  That  from  the  head  and  jaw  is  the 
finest  quality,  and  is  used  for  lubricating  clocks  and  fine  machinery. 


(7)  TERRESTRIAL  ANIMAL  OILS 

These  oils  have  low  iodine  value  and  yield  solid  elaidin.  They 
are  derived  from  the  feet  of  cattle,  horses,  and  sheep,  or  are  expressed 
from  lard  and  tallow. 

Neat's-foot  oil  is  made  by  boiling  the  feet  and  shin  bones  of  cattle 
in  water.  It  is  a  pale  yellow,  limpid  oil  of  0.916  sp.  gr.  at  15°  C.,  is 
nearly  odorless,  and  deposits  stearin  on  standing.  Its  saponification 
value  is  194 ;  iodine  value,  70 ;  it  yields  a  solid  or  semi-solid  elaidin ; 
Maumene  test,  47°  to  48.5°  C.  It  is  nearly  pure  olein,  and  does  not 
readily  become  rancid  nor  gummy  when  used  on  machinery.  It  is 
used  for  a  fine  lubricator  and  for  leather  dressing.  It  is  often  adul- 
terated with  fish,  rape,  cotton-seed,  and  mineral  oils,  and  other  hoof 
oils.  Bleached  tallow  oil  is  often  sold  as  "  neat's-foot." 

Lard  oil  is  prepared  by  cold  pressing  lard  (p.  367).  The  best 
quality  is  limpid  and  colorless,  and  consists  of  olein,  with  some  pal- 
rnitin  and  stearin,  the  quantity  of  these  latter  depending  upon  the 
temperature  of  the  pressing;  poor  grades  have  a  brown  color  and 
offensive  odor.  It  has  a  specific  gravity  of  0.915  at  15.5°  C. ;  a  saponi- 
fication value  of  195  to  196 ;  iodine  value,  56  to  74 ;  it  yields  solid 
elaidin.  It  is  used  as  an  illuminant,  as  a  lubricant,  and  for  oiling  wool. 
It  is  frequently  adulterated  with  cotton-seed  oil,  cocoanut  olein, 
"  neutral  mineral  oil,"  or  rape  oil. 

Tallow  oil  consists  mainly  of  olein,  and  is  obtained  by  pressing 
tallow  (p.  367).  It  is  chiefly  mixed  with  mineral  oil  for  use  as  a  lubri- 
cant. If  selected,  fresh  tallow  is  rendered  at  65°  C.,  and  the  clear 
oil  kept  for  twenty-four  hours  in  a  graining  vat,  the  stearin  and  part 
of  the  palmitin  crystallize.  By  pressing,  the  liquid  olein  and  some 
palmitin  is  obtained  as  "  oleo  oil,"  which  is  used  for  artificial  butter 
making.  The  press-cake  (oleo-stearin)  is  used  in  making  "  compound 
lard  "  (p.  360),  and  sometimes  as  a  soap  or  candle  stock.  Low  grades 
of  tallow  oil  are  not  white,  and  are  called  "  red  oil  "  in  trade ;  these 


366  OUTLINES   OF   INDUSTRIAL  CHEMISTRY 

must  not  be  confounded  with  the  red  oil  which  consists  of  oleic  acid 

(p.  382). 

(8)  SOLID  VEGETABLE  FATS 

Palm  oil  is  obtained  from  the  fruit  of  several  varieties  of  palm, 
Elceis  Guineensis,  Jacq.,  native  to  the  west  coast  of  Africa.  It  is  a 
mixture  of  palmitic  acid,  palmitin,  and  olein,  and  is  semi-solid  in 
this  climate.  When  fresh,  it  is  red  or  orange  yellow,  but  on  stand- 
ing, especially  if  exposed  to  the  sunlight,  it  becomes  brownish  yellow 
or  drab.  It  may  be  bleached  by  heating  and  blowing  in  air ;  or  by 
treating  with  potassium  bichromate  and  hydrochloric  acid.  Fresh 
oil  has  a  pleasant  odor,  but  is  liable  to  become  rancid,  when  it  con- 
tains a  large  percentage  of  fatty  acids  and  has  a  disagreeable  odor. 
Its  specific  gravity  at  99°  C.  is  0.859 ;  the  saponification  value  is  196 
to  202  ;  iodine  value,  53  to  56.  It  is  used  as  a  candle  and  soap  stock, 
and  in  making  lubricants. 

Palm  kernel  or  palm  nut  oil  is  derived  from  the  kernels  of  the 
fruit  of  Elceis  Guineensis,  Jacq.  It  is  similar  to  and  used  in  the  same 
way  as  cocoanut  oil. 

Cocoanut  oil  is  derived  from  the  cocoanut,  Cocos  nucifera,  L.  (or 
buty racea,  L.  f.),  the  chief  commercial  supply  coming  from  India, 
Ceylon,  and  the  South  Sea  Islands.  The  dried  meat  ("  copra  ")  of 
the  nut  is  pressed  or  boiled  in  water.  The  oil,  which  is  a  solid  fat  in 
this  climate,  contains  the  glycerides  of  myristic,  palmitic,  stearic,  lauric, 
capric,  caprylic,  and  caproic  acids.  It  melts  at  20°  to  28°  C. ;  its  sa- 
ponification value  is  250  to  268 ;  its  iodine  value,  8.9.  It  is  very  liable 
to  become  rancid.  It  is  much  used  for  soap  stock,  especially  for  the 
"  cold-process  "  soaps,  and  since  it  is  not  readily  precipitated  by  salt, 
for  marine  soaps ;  but  it  needs  a  strong  lye  for  its  saponification.  It 
is  also  said  to  be  used  for  artificial  butter  and  as  a  substitute  for  lard. 
By  cold  pressing,  a  solid  stearin  is  obtained  which  is  used  in  making 
candles. 

Cacao-butter  is  obtained  from  the  cacao  bean,  the  seeds  of  The- 
broma  Cacao,  L.,  and  is  a  solid  fat  having  a  pleasant  odor  and  the 
flavor  of  chocolate.  It  consists  of  the  glycerides  of  palmitic,  stearic, 
and  lauric  acids,  with  traces  of  linoleic  and  arachidic  acids.  It  is 
used  for  ointments  and  salves  in  pharmacy,  and  in  the  manufacture 
of  "  chocolate  creams,"  and  for  toilet  soaps.  It  is  often  adulterated 
with  tallow,  vegetable  oils,  beeswax,  or  paraifine  wax.  Its  specific 
gravity  is  0.890  to  0.900  at  15°  C. ;  saponification  value,  192  to  202 ; 
iodine  value,  32  to  37.7. 


OILS  AND   FATS  367 

Japan  wax  is  obtained  from  a  species  of  Rhus  by  boiling  the  fruit 
in  water.  It  is  a  pale  yellow  or  white,  has  a  greasy  feel,  and  can  be 
kneaded  in  the  fingers.  It  consists  of  palmitin,  CaHXCieHaiC^a, 
with  some  stearin,  and  is  easily  saponified.  It  is  not  a  true  wax.  It 
melts  at  53°  to  54°  C.,  and  its  specific  gravity  is  0.970  to  0.980  at  15° 
C.  It  is  soluble  in  benzene,  petroleum  spirit,  and  in  boiling  97  per 
cent  alcohol.  It  is  used  for  candles,  for  wax  matches,  as  a  furniture 
polish,  and  for  adulterating  beeswax. 


(9)   SOLID    ANIMAL  FATS 

Lard  is  prepared  from  the  fat  of  the  hog.  It  is  rendered  at  a  low 
temperature,  and  is  a  softer  grease  than  tallow.  It  is  a  mixture  of 
palmitin,  stearin,  and  olein.  It  melts  at  28°  to  45°  C.,  forming  a 
clear  liquid.  Its  specific  gravity  is  about  0.932  ;  saponification  value, 
195  to  196;  iodine  value,  59;  Maumene  test,  24°  to  27°  C.  When 
pure,  it  is  white,  nearly  odorless  and  tasteless.  By  pressing  it  yields 
lard  oil  (p.  365).  It  is  often  adulterated  with  water,  25  per  cent  or 
even  more  being  worked  into  it;  .or  with  cotton-seed  oil  and  oleo- 
stearin ;  or  with  beef  fat  and  cotton-seed  oil.  The  chief  uses  of  lard 
are  for  culinary  purposes,  for  soap  stock,  for  butterine,  and  in  oint- 
ments and  salves.  "  Compound  lard  "  is  a  mixture  of  oleo-stearin 
and  white  cotton-seed  oil. 

Tallow  is  the  solid  fat  of  the  sheep  or  ox.  Before  rendering,  it 
is  customary  to  break  up  the  tissues  by  grinding  with  hollow  rolls 
having  a  rough  surface  and  heated  by  steam.  The  rendered  tallow 
solidifies  at  about  34°  to  45°  C.,  and  is  graded  according  to  its  ap- 
pearance, hardness,  odor,  and  rancidity.  It  consists  of  about  two- 
thirds  palmitin  and  stearin,  and  one-third  olein.  Its  density  at  99° 
C.  is  0.860  to  0.862;  saponification  value,  195  to  198;  iodine  value, 
40.  It  is  extensively  used  for  soap  and  candle  stock,  for  lubricating, 
and  as  a  leather  dressing. 

Bone  tallow  is  a  soft  grease  obtained  by  boiling  fresh  bones  in 
water  to  extract  the  marrow  and  fat.  It  is  dark-colored  and  foul- 
smelling  and  usually  contains  calcium  phosphate.  It  is  mainly  used 
for  cheap  colored  soaps. 

Butter  fat  is  derived  from  cows'  milk.  It  is  very  complex,  con- 
taining glycerides  of  a  number  of  acids  of  which  oleic  (60  per  cent), 
palmitic,  stearic,  and  butyric  (5  per  cent)  are  the  most  important ; 
small  quantities  of  the  glycerides  of  capric  and  caproic  acids  are  also 
present.  Butter  fat  has  a  specific  gravity  of  0.870  at  99°  C. ;  its 


368  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

saponification  value  is  221  to  227 ;  iodine  value,  26  to  35.  It  is  the 
basis  of  butter,  of  which  it  forms  about  90  per  cent,  the  remainder 
being  water,  salt,  curds,  and  coloring  matter.  It  is  made  by  churning 
cream  to  cause  the  agglomeration  of  the  fat  globules  into  a  solid  mass. 
Sour  cream  churns  more  easily  than  sweet  cream.  The  latter  is  re- 
moved from  the  milk  by  a  separator  *  or  by  skimming  before  the 
milk  sours.  Butter  from  sour  cream  will  not  keep  unless  well  salted, 
since  it  contains  sufficient  casein  to  increase  its  liability  to  become 
rancid,  by  which  a  considerable  amount  of  butyric  acid  is  formed. 
Butter  is  usually  colored  with  carrot  juice,  saffron,  turmeric,  or  an- 
nato ;  or  sometimes  with  certain  coal-tar  colors. 

Butterine,  oleomargarine,  and  margarine  are  butter  substitutes 
made  from  mixtures  of  animal  and  vegetable  oils,  flavored  with  some 
butter,  and  colored  to  imitate  it.  Oleo  oil  from  tallow,  and  neutral 
lard  are  much  used.  These  are  mixed  with  cotton-seed  oil  in  cold 
weather  (or  with  peanut  or  sesame  oil  abroad)  to  increase  the  per- 
centage of  olein. 

WAXES 

(10)   LIQUID  WAXES 

Sperm  oil  is  obtained  from  the  blubber  and  head  cavity  ("  case  ") 
of  the  cachalot,  or  sperm  whale,  Physeter  macrocephalus,  the  case 
alone  sometimes  yielding  several  barrels  of  free  oil.  The  composition 
of  sperm  oil  is  not  definitely  known,  but  it  differs  materially  from 
most  oils.  It  contains  no  glycerides,  consisting  mainly  of  esters  of 
monatomic  alcohols.  Some  authorities  hold  that  dodecatyl  alcohol, 
Ci2H25OH,  and  its  allied  homologues,  such  as  cetyl  alcohol,  CieHss  •  OH, 
are  present,  but  this  is  denied  by  Lewkowitsch.  The  oil  holds  in 
solution  a  considerable  amount  of  spermaceti  (below),  which  is  usually 
filtered  out  of  the  cold  oil  before  it  is  sold.  Sperm  oil  is  a  limpid, 
golden  yellow  liquid,  having  a  slight  fishy  odor;  its  specific  gravity 
is  0.875  to  0.884  at  15.5°  C. ;  saponification  value,  123  to  147 ;  iodine 
value,  81.3  to  85  ;  it  yields  a  solid  elaidin ;  Maumene  test,  45°  to  47°  C. 
It  is  a  valuable  lubricator,  especially  for  rapid-running  machinery, 
since  its  viscosity  is  less  than  other  non-drying  fatty  oils,  and  varies 

*  Before  churning,  sweet  cream  is  always  allowed  to  "  ripen  "  ;  i.e.  to  stand  a 
few  hours  undisturbed  after  separating.  Usually  a  "  starter  "  is  added  to  set  up 
lactic  fermentation ;  by  using  pure  cultures  of  acid-forming  bacteria,  the  quality 
and  flavor  of  the  butter  can  be  much  better  controlled  than  when  the  ripening  is 
spontaneous. 


OILS  AND   FATS  369 

but  little  with  changes  of  temperature ;  and  because  it  does  not  be- 
come gummy  nor  rancid.  It  is  also  used  for  illuminating,  for  leather 
dressing,  and  in  tempering  steel.  Because  of  its  high  price,  it  is  often 
adulterated  with  mineral  oils  or  with  other  fish  oils. 

The  related  Doegling  or  Bottlenose  oil  is  also  a  liquid  wax. 


(11)   SOLID  ANIMAL  WAXES 

Spermaceti  is  a  crystalline  wax  found  in  the  head  of  the  sperm 
whale  and  which  separates  from  sperm  oil  when  chilled;  it  is  ob- 
tained by  expressing  the  oil.  The  brown  or  yellow  scales  of  crude 
spermaceti  are  treated  with  a  little  caustic  potash  to  remove  adher- 
ing oil,  and  are  thus  rendered  white  and  translucent  while  they  re- 
tain their  crystalline  structure.  Spermaceti  consists  mainly  of  cetyl 
palmitate,  Ci6H33O  •  Ci6H3iO.  It  is  odorless  and  tasteless  and  melts 
at  about  45°  C.  Its  specific  gravity  is  0.943  at  15°  C. ;  saponification 
value,  108  to  128 ;  it  burns  with  a  large  clear  flame.  Its  chief  uses  are 
in  candle  making,  in  confectionery,  and  in  pharmacy. 

Beeswax  is  obtained  from  the  honey-comb  of  bees  by  melting  it 
in  hot  water;  the  floating  layer  of  tough  brown  or  yellow  wax  is 
drawn  off  into  moulds.  It  may  be  bleached  by  exposure  in  thin 
films  to  the  sun  and  moist  air,  or  by  the  moderate  action  of  chromic 
or  nitric  acid,  or  hydrogen  peroxide.  Bleached  wax  is  white,  and  has 
neither  taste  nor  smell.  It  consists  mainly  of  myricyl  palmitate, 
CaoHeiO  •  CieHsiO,  and  some  cerotic  acid,  C27H54O2.  It  melts  at  63°  to 
64°  C.,  and  has  a  specific  gravity  of  0.965  to  0.969  at  15°  C.  It  is 
often  adulterated  with  water  or  white  mineral  powders  to  increase 
its  weight.  Stearin,  paraffine,  cerasin,  tallow,  and  vegetable  wax  are 
often  added  as  adulterants.  It  is  used  in  candle  making,  in  phar- 
macy, and  for  many  other  purposes  in  the  arts. 

Chinese  wax,  or  insect  wax,  is  secreted  by  an  insect,  Coccus  ceri- 
ferus,  Fabr.  The  wax  is  deposited  on  the  branches  of  certain  trees, 
which  are  cut  off  and  the  wax  removed  by  hand.  It  is  melted  in 
boiling  water  to  separate  the  dirt,  bark,  etc.  It  is  white,  crystalline, 
and  very  hard,  without  taste  or  smell.  It  is  soluble  in  benzine,  and 
slightly  so  in  alcohol  and  ether.  It  consists  of  ceryl  cerotate, 
C27H55O  •  C27H53O.  Its  specific  gravity  is  0.970  at  15°  C.,  and  it  melts 
at  82°  to  83°  C.  It  is  used  for  fine  candles,  in  medicine,  as  size  for 
paper,  and  as  a  furniture  polish. 

Wool  grease  is  the  greasy  substance  exuded  with  the  perspiration 
from  sheep.  It  is  a  complex  mixture  of  alcohols  and  esters,  especially 
2u 


370  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

of  cholesterol  and  isocholesterol,  and  palmitic,  stearic,  myristic, 
carnaubic,  and  other  acids;  also  potassium  salts  of  these  acids.  It 
does  not  contain  glycerides  and  the  alcohols  appear  on  analysis  along 
with  the  unsaponifiable  matter. 

The  grease  may  be  obtained  by  extracting  the  raw  wool  with 
naphtha  or  other  solvent;  or  the  alkaline  wash-waters  in  which  the 
wool  has  been  washed  may  be  treated  with  sulphuric  acid,  in  which 
case  the  grease  also  contains  fatty  acids  from  the  soap  used  (p.  500). 
It  is  yellow  or  brown  in  color,  has  an  unpleasant  odor,  and  emulsifies 
with  water.  It  is  used  for  leather  dressing,  and  in  making  axle  grease 
and  other  lubricants.  Purified  wool  grease  has  a  specific  gravity  of 
0.973  at  15°  C. ;  iodine  value,  25  to  28 ;  saponification  value,  98  to  102. 

Lanolin  is  made  by  washing  wool  grease  with  water  until  all  the 
soluble  matter  is  removed,  melting  by  heating  in  water,  skimming 
and  allowing  it  to  cool  and  solidify.  Lanolin  is  much  used  in  phar- 
macy as  a  basis  for  salves,  ointments,  and  emulsions.  It  contains 
about  25  per  cent  of  water,  and  forms  a  very  soft  ointment. 

(12)  SOLID  VEGETABLE  WAX 

Carnauba  wax  is  derived  from  a  species  of  palm,  Copernicia  ceri- 
fera,  Mart.,  native  in  Brazil.  It  forms  a  coating  on  the  leaves,  and 
is  removed  by  shaking  or  pounding.  The  raw  wax  is  of  a  grayish 
or  greenish  yellow  and  is  very  hard,  though  readily  powdered.  When 
purified,  it  has  no  odor  nor  taste,  melts  at  83°  to  88°  C.,  and  has  a 
specific  gravity  of  0.990  to  0.999  at  15°  C.  Its  constitution  is  com- 
plex, but  it  contains  myricyl  cerotate,  CaoHeiO  •  C27H53O,  myricyl 
alcohol,  CsoHeiOH,  cerotic  acid,  C27H54O2,  and  other  bodies.  It  is  used 
for  candle  making  and  for  adulterating  beeswax,  and  in  varnish. 


REFERENCES 

Die  Chemie  der  Austrocknenden  Oele.     G.  J.  Mulder,  Berlin,  1867. 
Die  Fettwaaren  und  fetten  Oele.     C.  Lichtenberg,  Weimar,  1880. 
Die  Trocknenden  Oelen.     L.  E.  Andes,  Braunschweig,  1882.     (Vieweg.) 
Technologic  der  Fette  und  Oele.     C.  Schaedler,  Berlin,  1883. 
Commercial  Organic  Analysis.     A.  H.  Allen.     Vol.  II.     London,  1886. 
Das  Wachs  und  seine  technische  Verwendung.     S.  Sedna,  Wein,  1886. 
Die  Fetten  Oele  des  Pflanzen  und  Thierreiches.     G.  Bornemann,  Weimar, 

1889. 

Die  Untersuchung  der  Fette,  Oele,  Wachsarten.   C.  Schaedler,  Leipzig,  1890. 
Les  Corps  Gras.     A.  M.  Villon,  Paris,  1890. 
Les  Matieres  Grasses.     G.  Beau  visage,  Paris,  1891. 

Painters'   Colours,   Oils,  and  Varnishes.     G.   H.   Hurst,   London,   1892. 
Die  Schmiermittel.     J.  Grossmann,  Wiesbaden,  1894. 
Chemical  Analysis  of  Oils,  Fats,  and  Waxes.     R.  Benedikt.     Translated 

by  J.  Lewkowitsch.     London,  1895. 


OILS   AND   FATS  371 

Chemical  Technology.  ,  C.  E.  Groves  and  Wm.  Thorp.  Vol.  II.  Light- 
ing. Philadelphia,  1895.  (P.  Blakeston,  Son  &  Co.) 

Animal  and  Vegetable  Fats  and  Oils.     W.  T.  Brannt,  Philadelphia,  1896. 

Oils  and  Varnishes.     J.  Cameron,  London,  1896.      (J.  and  A.  Churchill.) 

Analyse  der  Fette  und  Wachsarten.  Benedikt  u.  Ulzer,  3**  Auf.,  Berlin, 
1897. 

Lubricants,  Oils,  and  Greases.     I.  Redwood,  1898. 

Oil  Chemist's  Handbook.     E.  Hopkins,  1900. 

Vegetable  Fats  and  Oils.     L.  E.  Andes,  2d  ed.,  1902. 

Oils,  Fats,  and  Waxes.     C.  R.  Alder  Wright,  2d  ed.,  London,  1903. 

Cottonseed  Products.     L.  L.  Lamborn,  New  York,  1904.     (VanNostrand.) 

Technologic  der  Fette,  Oele,  und  Wachsarten  des  Pflanzen  und  Tierreichs. 
G.  Hefter,  4  vols.,  1906+. 

Chemie,  Analyse  und  Gewinnung  der  Oele,  Fette,  und  Wachse.  L.  Ubbe- 
lohde,  4  vols.,  1908+. 

Handbuch  der  Chemie  und  Technologie  der  Oele  und  Fette.  L.  Ubbe- 
lohde  und  F.  Goldschmidt,  Leipzig. 

A  Short  Handbook  of  Oil  Analysis.  A.  H.  Gill,  6th  ed.,  Philadelphia, 
1911.  (Lippincott  Co.) 

Lubricating  Oils,  Fats,  and  Greases.     G.  H.  Hurst,  3d  ed.,  London,  1911. 

Chemical  Technology  and  Analysis  of  Oils,  Fats,  and  Waxes.  J.  Lew- 
kowitsch,  5th  ed.,  3  vols.,  London,  1914.  (Macmillan  &  Co.,  Ltd.) 


SOAP 

Soaps  are  metallic  salts  of  certain  non-volatile  fatty  acids,  the 
commercial  article  usually  containing  a  mixture  of  several  of  these 
salts.  Soaps  intended  for  washing  purposes  should  contain  only 
soluble  salts  of  the  acids  ;  i.e.  those  of  sodium,  potassium,  or  ammonium  ; 
the  calcium,  magnesium,  lead,  and  other  heavy  metal  soaps  are  in- 
soluble in  water. 

As  already  explained,  the  common  fats  and  oils  contain  the  fatty 
acids  in  combination  with  glycerine,  forming  glycerides,  and  it  is 
from  these  that  soaps  are  generally  made.  The  process  of  decom- 
posing the  glycerides  and  forming  soap  is  called  saponification, 
although  this  term  is  generally  used  to  denote  the  decomposition  of 
any  organic  ester  into  its  basic  alcohol  and  free  acid.  Saponification 
is  effected  in  several  ways  :  - 

(1)  By  the  action  of  water  or  steam  at  high  temperature  or 
pressure  :  — 

3  H20  =  C3H5(OH)3  +  3  C18H36O2. 


This  hydrolysis  may  be  accomplished  at  a  much  lower  tempera- 
ture if  the  water  is  acidulated  with  a  dilute  mineral  acid,  which  serves 
as  a  catalyzer  and  accelerates  the  reaction  between  the  water  and  the 
glycerides  of  the  fat.  The  amount  needed  is  small,  and  it  is  all  found 
unchanged,  mixed  with  the  products  of  the  reaction.  This  method  is 
chiefly  employed  for  the  preparation  of  glycerine  and  to  obtain  the 
free  fatty  acid. 

(2)  By  the  action  of  caustic  alkalies  :  — 

C3H5(Ci8H35O2)3  +  3  NaOH  =  C3H5(OH)3  +  3  Ci8H35O2  •  Na. 

This  is  the  reaction  employed  in  ordinary  soap  making,  the  caustic 
uniting  with  the  fatty  acid  radical  to  form  the  soap,  i.e.  an  alkali 
salt  of  the  acid.  The  glycerine  formed  is  a  by-product,  and  progres- 
sive soap  makers  have  a  glycerine  recovery  plant  or  sell  the  lye  to  a 
glycerine  manufacturer. 

(3)  By  the  action  of  lime;    (Milly's  process,  p.  381). 

The  chemistry  of  saponification  was  first  explained  by  Chevreul, 
who  attributed  the  cleansing  action  of  soap  to  free  alkali  formed  by 
the  decomposition  of  the  soap  when  brought  into  solution.  The 
fatty  acids  are  weak  and  soap  solutions  are  therefore  strongly  alkaline 

372 


SOAP  373 

by  hydrolysis ;  the  insoluble  fatty  acids  produced  by  this  hydrolysis 
make  the  solution  turbid.  Soap  removes  the  dirt  by  adsorbing  on 
the  surface  of  the  dirt  particles  and  thus  emulsifying  it ;  in  this  the 
soap  acts  as  a  protective  colloid. 

The  alkalies  commonly  used  for  soap  making  are  caustic  potash 
and  soda.  The  former  yields  a  "  soft  soap,"  which  is  liquid  under 
ordinary  conditions,  because  of  the  lower  melting  point,  greater  solu- 
bility, and  possible  deliquescence  of  potassium  soaps.  The  glycerine 
formed  remains  mixed  in  the  soft  soap. 

Previous  to  Leblanc's  invention  of  the  soda  process,  soap  was 
made  with  caustic  potash  derived  from  wood  ashes  and  lime.  Com- 
mon salt  was  added  after  the  saponification  of  the  fat  was  complete, 
forming  hard  sodium  soap,  according  to  the  reaction :  — 

KCi8H35O2  +  NaCl  =  KC1  +  NaCi8H35O2. 

But  now  most  soft  soaps  are  made  from  soda  soaps  by  adding  a  large 
quantity  of  water. 

The  fatty  material  (soap  stock)  varies  according  to  the  kind  of 
soap  desired  and  the  facility  with  which  certain  stocks  may  be 
obtained.  For  white  soaps,  the  best  grades  of  tallow,  tallow-oil, 
palm  oil,  or  cocoanut  oil  are  chiefly  used  in  this  country.  Cotton- 
seed oil  may  become  rancid  and  cause  yellow  or  brown  spots  in 
the  product,  besides  giving  it  a  bad  odor  and  greasy  appearance. 
Corn  oil  is  also  subject  to  rancidity.  In  Europe,  Castile  soap  is 
made  from  second-quality  olive  oil,  to  which  some  cocoanut  oil  is 
usually  added. 

Laundry  soaps  are  made  from  tallow,  bone  grease,  and  house 
grease,  and  often  palm  and  cotton-seed  oils.  Yellow  soaps  are  made 
from  these  materials,  with  the  addition  of  a  certain  proportion  of 
rosin.  The  latter  combines  readily  with  alkali,  but  forms  a  rather 
soft  soap,  with  good  lathering  properties ;  rosin  is  cheaper  than  most 
of  the  fats,  and  when  used  in  proper  quantities,  adds  certain  valuable 
properties  to  the  soap,  and  is  not  an  adulterant. 

The  non-drying  oils,  with  caustic  soda,  generally  yield  the  hardest 
soaps,  while  the  semi-drying  and  drying  oils  form  products  of  butter- 
like  consistency. 

Cocoanut  oil  saponifies  readily  with  strong  lye,  without  boiling; 
hence  is  used  for  "  cold-process  "  soaps.  "  German  mottled,"  or 
'*  olein  soaps,"  are  made  from  crude  oleic  acid  ("  red  oil  "),  obtained 
in  the  candle  industry  (p.  382).  The  spent  lyes  from  white  or  yel- 
low soaps  are  often  used  in  making  red-oil  soap,  in  order  to  save  all 


374  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

the  alkali,  since  the  oleic  acid  will  combine  with  the  carbonate  as  well 
as  with  the  caustic. 

Toilet  soaps  should  be  made  from  the  best  material,  but  many 
cheap  grades  are  made  from  poorer  stock  than  laundry  soap,  and  the 
defects  covered  by  high  color  and  perfume.  Some  toilet  soaps  are 
made  by  melting  together  two  or  more  kinds  of  soap. 

Good  soap  cannot  be  made  from  poor  material.  The  lye  must  be 
a  caustic  liquor,  free  from  other  salts,  sulphides  and  sulphites  being 
especially  injurious,  since  they  cause  discoloration  of  the  soap.  In 
many  large  works  the  lye  is  prepared  by  causticizing  soda-ash  with 
lime.  When  caustic  is  purchased,  it  is  simply  dissolved  to  form  a 
solution  of  the  desired  strength,  varying  from  18°  to  30°  Be. 

Soap  kettles  are  square  or  round,  and  vary  in  size  from  10  feet  in 
diameter  by  15  feet  deep,  to  25  by  35  feet,  and  capable  of  holding 
300,000  pounds  of  soap.  In  modern  factories  they  are  always  heated 
by  steam ;  very  small  ones,  used  for  remelting  toilet  soaps,  etc.,  being 

steam-jacketed,  and  the 
larger  ones  having  both 
open  and  closed  coils. 
A  modern  form  (Fig. 
110)  has  a  conical  bot- 

P  1  T  *®JA  J  I  torn,  in  which  the  steam 
coils  (A,  B)  are  arranged. 
Such  a  kettle,  calculated 
to  hold  100,000  pounds 
of  soap,  is  about  15  feet 
in  diameter  and  21  feet  high,  the  cone  bottom  being  about  5  feet 
deep,  and  the  cylindrical  walls  about  16  feet  high.  It  is  made  of 
f -inch  boiler  plate,  and  is  sheathed  with  2-inch  pine  staves.  It  rests 
on  stone  pillars  and  foundations,  and  has  large  draw-off  cocks  in  the 
cone,  for  running  off  waste  lyes  while  the  soap  is  pumped  away 
through  a  pipe  (D)  passing  through  the  side  of  the  kettle. 

Soaps  are  made  by  various  processes,  but  the  most  common  are 
the  following :  — 

(1)  The  fat  is  treated  with  the  exact  amount  of  caustic  alkali 
needed  to  saponify  it,   leaving  the  glycerine  in  the  soap.     The  so- 
called  "  cold-process "  soap  is  the  most  common  example  of  this 
method. 

(2)  The  fat  is  boiled  with  solutions  of  caustic  alkali  until  saponi- 
fication  is  complete,  or  until  the  soap  attains  certain  desired  proper- 
ties.    The  glycerine  remains  mixed  with  the  product,  as  in  the  case 


SOAP  375 

of  soft  and  "  marine  "  soaps ;  or  it  is  excluded,  as  in  the  case  of  yel- 
low, laundry,  mottled,  and  curd  soaps. 

(3)  A  free  fatty  acid  is  neutralized  by  treatment  with  an  alkaline 
hydroxide  or  carbonate,  as  in  the  case  of  oleic  acid. 

The  cold  process  is  the  simplest  of  soap-making  methods,  but 
requires  carefully  calculated  quantities  of  caustic  and  fat,  and  the 
latter  must  be  well  refined.  Since  it  is  difficult  to  calculate  the  exact 
amount  of  alkali,  such  soaps  usually  contain  free  fat  or  free  alkali,  or 
both.  Cocoanut  oil  and  tallow  are  chiefly  used,  and  are  melted  and 
run  into  a  mixing  tank  heated  by  steam,  or  into  a  crutcher  (p.  376). 
Then  a  definite  quantity  of  strong  caustic  soda  lye,  32°  to  36°  Be.,  is 
added,  and  the  mixture  well  stirred  for  a  few  minutes.  The  heat  of 
the  reaction  is  sufficient  to  carry  it  on  when  once  started.  After 
saponification  is  well  under,  way,  the  stirring  is  stopped  and  the  mix- 
ture is  run  into  "  frames  "  (p.  376),  where  it  stands  several  days,  to 
complete  the  reaction  and  to  cool.  This  leaves  all  the  glycerine  and 
any  excess  lye  in  the  soap.  The  product  looks  well  when  fresh,  but 
is  very  apt  to  turn  yellow  and  become  rancid. 

Most  soaps  are  boiled.  The  process  is  usually  divided  into  several 
stages.  The  melted  fat  and  lye  of  about  15°  Be.  (1.115  sp.  gr.)  are 
run  into  the  soap  kettle  together,  while  free  steam  is  blown  in  to  mix 
them,  and  to  form  an  emulsion  of  the  oil  and  lye,  which  is  essential 
to  the  beginning  of  saponification  or,  as  the  soap-boiler  terms  it, 
"  to  kill  the  stock."  When  the  emulsion  forms,  the  lye  has  "  caught 
the  stock."  If  the  lye  is  too  strong  at  first,  it  does  not  "  catch,"  and 
water  is  added  and  the  heating  continued  until  the  emulsion  forms. 
Strong  lye  is  then  carefully  added  in  small  portions  at  a  time,  and 
boiling  is  continued  to  complete  the  saponification.  If  a  wooden 
stirring  paddle  be  pushed  into  the  mass  at  this  time,  the  soap  adheres 
to  it  when  drawn  out,  and  long  strings  of  soap  hang  down  from  it. 
There  is  no  separation  of  the  lye.  When  the  process  is  finished,  as  is 
shown  by  the  soap  having  a  dry,  firm  feel  between  the  fingers,  the  soap 
is  "  grained  "  or  "  salted  out,"  by  adding  common  salt.  This  causes 
a  separation  of  the  soap  from  the  lye  and  glycerine,  which  is  shown 
by  the  soap  sticking  to  the  paddle  while  the  lye  runs  off.  When 
properly  salted,  the  soap  boils  in  broad,  smooth  patches,  and  is  hard, 
and  not  sticky,  when  cold.  The  steam  is  then  cut  off  and  the  soap 
allowed  to  stand  for  several  hours,  when  it  rises  to  the  top.*'  The 
salt  lye,  which  contains  most  of  the  glycerine,  is  drawn  off,  leaving 
the  soap  in  the  kettle.  Strong  lye,  25°  Be.  (1.205  sp.  gr.)  is  now  added, 
and  for  yellow  laundry  soaps,  rosin  is  introduced ;  for  white  soap, 


376 


OUTLINES   OF    INDUSTRIAL   CHEMISTRY 


tallow  or  cocoanut  oil  is  used  instead  of  the  rosin.  The  boiling  is  con- 
tinued for  two  or  three  days,  until  the  soap  becomes  clear  and  semi- 
transparent.  This  second  boiling  is  called  the  "  rosin  change  "  or 

the  "  strong  change  "  ;  during  this 
time,  the  soap  rises  fully  one-third 
the  depth  of  the  kettle,  and  often 
stands  higher  than  its  sides.  For 
this  reason,  the  kettle  is  not  filled 
more  than  two-thirds  full  at  first. 
When  the  rosin  or  cocoanut  oil  is 
saponified,  the  kettle  is  allowed  to 
stand  quietly  for  a  number  of  hours, 
when  the  lye  is  drawn  off.  The 
next  step  is  called  "  finishing," 
"settling,"  "pitching,"  or  "fit- 
ting." Water  is  added  to  the  boil- 
ing soap  until  it  loses  its  granular 
appearance,  after  which  it  is  allowed 
to  settle  for  several  days.  This 
removes  excess  caustic  and  any  insoluble  impurities.  The  contents  of 
the  kettle  separate  into  three  layers,  the  soap  on  top,  and  the  Ive  at 
the  bottom,  and  between  them  a  dark-colored  layer,  called  "  nigre," 
containing  caustic  lye,  soap,  water,  and  various  organic  impurities. 

The  lye  and  nigre  are  drawn  off  into  separate  tanks,  and  the  soap 
is  pumped  into  the  crutcher,  which  is  a  very  efficient  mixing  machine. 
One  form  (Fig.  Ill)  consists  of  a  broad,  vertical  screw,  working  within 
a  cylinder,  which  is  placed  in  a 
larger  tank.  The  action  of  the 
screw  draws  the  liquid  soap  in  at 
the  bottom  and  discharges  it  over 
the  top  of  the  cylinder,  to  again 
pass  through  the  apparatus.  A 
thorough  mixing  is  thus  secured. 
The  perfume,  and  any  filling  mate- 
rial, such  as  silicate  of  sodium, 
sodium  carbonate,  borax,  talc,  etc., 
are  added  in  the  crutcher.  These 
ingredients  are  well  mixed  with  the 
soap,  which  becomes  lighter  colored,  and  then  stiff  and  thick.  After 
crutching  for  from  3  to  15  minutes  the  soap  is  run  into  "frames" 
(Fig.  112),  which  are  large  sheet-iron  boxes,  mounted  on  wheels,  and 


FIG.  112. 


SOAP 


377 


having  removable  sides.  Each  frame  holds  from  1000  to  1700 
pounds,  or  one  crutcher  full.  When  it  has  solidified,  after  24  to  36 
hours,  the  sides  are  removed,  and  the  block  of  soap  stands  several  days 
in  the  air  to  cool  thoroughly.  Then  it  goes  to  the  "  slabber  "  (Fig. 
113),  a  machine  containing  a  number  of  tightly  stretched  steel  wires, 
which  are  pushed  against  the  block  of  soap,  cutting  it  into  slabs  of 
the  desired  thickness.  These  then  pass  through  a  "  cutter,"  a  similar 


Fia.  113. 

machine,  which  forms  them  into  rough  bars,  which  are  put  into  the 
dry  room,  kept  at  a  temperature  of  about  90°  F.,  for  12  to  15  hours. 
They  are  then  run  through  the  press,  which  forms  the  commercial  bar 
and  stamps  on  it  the  trade  mark,  name,  or  other  design.  They  finally 
pass  on  an  endless  belt  to  the  wrappers,  who  enclose  them  in  separate 
papers  and  pack  them  in  boxes,  which  are  immediately  nailed  up  for 
market. 

"  Boiled-down  soap  "  is  made  by  treating  the  soap,  after  the  lye 
has  been  drawn  off,  with  strong  brine,  and  then  boiling  it  down. 
Sometimes  the  soap  is  settled  and  the  nigre  and  lye  separated  before 


378  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

boiling  down.  This  reduces  the  percentage  of  water  in  the  soap, 
leaving  it  dry  and  hard.  If  soaps  in  which  no  rosin  is  used  are  boiled 
down  on  the  lye  until  the  latter  becomes  concentrated  enough  to  pre- 
cipitate the  soap,  and  then  run  into  frames  and  cooled  very  slowly, 
the  small  quantity  of  lye  and  other  impurities  mechanically  enclosed 
segregate  during  the  cooling  into  those  parts  of  the  mass  which  are 
the  last  to  solidify,  and  cause  the  appearance  called  "  mottling."  By 
adding  a  small  amount  of  copperas,  ultramarine,  lampblack,  or  other 
pigment,  the  mottling  becomes  more  prominent.  Castile  or  Marseilles 
soaps  have  a  green  mottle,  changing  to  red  on  exposure  to  the  air. 
This  is  due  to  the  presence  of  copperas,  which  precipitates  the  ferrous 
hydroxide  with  the  lye  in  the  soap ;  on  contact  with  the  air,  the  green 
hydroxide  is  changed  to  the  red  ferric  salt.  Rosin  produces  a  more 
uniform  soap,  without  mottle. 

Toilet  soaps  are  made  in  the  same  general  way  as  the  yellow  soap, 
but  from  finer  stock  and  with  greater  care  to  secure  the  complete  re- 
moval of  free  alkali.  Any  excess  of  alkali  is  usually  carbonated  during 
the  shaving  and  milling  process. 

Three  classes  of  toilet  soaps  are  made,  —  milled,  remelted,  and  trans- 
parent. Milled  soaps  are  made  by  shaving  thoroughly  dried  bars  of 
good  soap  to  fine  chips,  and  drying  again  until  only  about  10  per  cent 
water  remains.  The  dried  soap  is  then  ground  in  an  edge-runner  mill, 
and  the  perfume  or  other  ingredients  desired  are  added  at  the  same 
time.  After  thorough  incorporation,  the  soap  is  forced  through  a  die 
plate  by  heavy  pressure,  forming  a  long  bar,  which  is  cut  into  cakes ; 
these  are  stamped  and  pressed  into  the  desired  shape.  This  process 
allows  the  use  of  very  delicate  perfumes  and  other  ingredients  which 
would  be  destroyed  by  heat.  It  also  furnishes  a  hard  cake  which 
does  not  wear  away  so  rapidly  when  in  use. 

Remelted  soaps,  chiefly  made  in  England,  are  prepared  by  remelt- 
ing  one  or  more  kinds  of  soap,  together  with  the  perfumes  and  other 
ingredients,  in  a  steam- jacketed  kettle.  By  rapid  agitation  of  the 
melted  mass  with  paddles,  air  bubbles  can  be  disseminated  through 
the  soap,  which  gives  the  cake  sufficient  buoyancy  to  float  on  water 
after  stamping. 

Transparent  soaps  may  be  made  in  two  ways:  (a)  A  common 
soap  is  dissolved  in  alcohol,  the  solution  decanted  from  insoluble  im- 
purities, and  the  alcohol  distilled  off,  leaving  the  soap  as  a  transparent 
jelly,  which  is  carefully  dried  in  moulds  to  form  the  cake.  (6)  A 
cold-process  soap  is  made  as  above  and  coloring  matter,  perfumes,  etc., 
are  added.  The  glycerine  formed,  remaining  in  the  soap,  causes  the 


SOAP  379 

latter  to  have  a  translucent  appearance.  By  adding  more  glycerine, 
with  a  little  alcohol,  or  a  solution  of  cane  sugar,  the  transparency  is 
increased. 

Special  scouring  soaps  for  cleaning  metal  and  unpainted  woodwork 
are  made  by  adding  powdered  sand,  glass,  or  pumice-stone  to  a  yellow 
soap.  Strongly  alkaline  soaps  often  contain  ground  soda-ash,  borax, 
and  sodium  silicate  as  "  fillers,"  or  frequently  as  intentional  adulter- 
ants. Sodium  silicate  is  generally  added  to  yellow  soaps,  as  it  hard- 
ens them  somewhat  and  possesses  detergent  properties  itself. 

Soap  powders  are  made  by  mixing  soda-ash  with  a  soap  solution 
containing  just  enough  water  to  furnish  the  crystal  water  for  sal  soda. 
Since  sal  soda  does  not  form  above  34°  C.,  the  mixture  can  be  made 
hot,  and  on  cooling  sets  to  a  dry,  solid  mass.  This  is  ground,  packed, 
and  sold  as  soap  powder.  Abrasive  materials,  as  powdered  quartz 
(silex),  or  ground  feldspar,  are  frequently  added  with  the  soda-ash. 
These  soap  powders  are  also  made  from  red  oil  (p.  382)  by  neutraliz- 
ing with  dry  soda-ash. 

A  few  insoluble  soaps  of  the  heavy  metals  are  prepared  for  use 
in  pharmacy,  the  most  important  being  lead  soap  or  "  lead  plaster," 
which  is  made  by  decomposing  a  neutral  soap  with  a  soluble  lead 
salt,  or  by  heating  olive  oil  with  a  paste  of  lead  oxide  in  water. 


CANDLES 

The  materials  used  for  candles  are:  free  fatty  acids,  especially 
palmitic  and  stearic ;  hydrocarbons,  such  as  paraffine  and  ozokerite ; 
and  certain  esters  of  the  fatty  acids,  especially  tallow  and  waxes. 
The  requisites  for  candle  stock  are :  that  it  shall  burn  freely  without 
smoke  or  smell ;  that  it  shall  not  soften  at  so  low  a  temperature  that 
it  loses  its  form  from  the  heat  of  its  own  flame ;  and  that  when  melted 
it  shall  be  a  fluid  capable  of  being  drawn  into  the  wick  by  capillarity. 
Some  glycerides,  such  as  tallow,  burn  with  a  foul-smelling,  smoky 
flame,  and  hence  are  only  used  in  the  cheapest  candles.  Also,  they 
soften  at  too  low  a  temperature,  and  the  candle  readily  bends  and 
gutters.  Both  these  objections  also  apply  to  paraffine  and  to  some 
of  the  solid  fatty  acids. 

Candles  are  made  by  dipping,  pouring,  and  moulding.  For 
dipped  candles,  the  wick  is  repeatedly  introduced  into  the  melted 
stock,  each  layer  of  fat  being  allowed  to  solidify  before  the  next  dip. 
Tallow  dips,  the  poorest  candle  made,  are  prepared  in  this  way. 

Poured  candles  are  made  by  pouring  the  melted  stock  in  a  slow 
stream  over  the  wick,  which  is  stretched  in  a  frame.  This  method 
is  used  for  wax  candles,  since  the  wax  contracts  too  much  on  cooling 
to  allow  casting.  While  still  plastic,  they  are  rolled  on  a  flat  table 
under  a  board,  to  give  them  a  uniform  diameter. 

Most  candles  are  now  moulded  in  a  cylindrical  metal  form  through 
which  the  wick  is  drawn  in  the  line  of  its  axis.  The  mould  can  be  sur- 
rounded with  hot  or  cold  water  to  facilitate  the  casting  and  removal 
of  the  candles.  Wicks  are  of  plaited  or  twisted  cotton  yarn,  usually 
flat,  except  for  tallow  dips,  when  they  are  round.  They  are  so  pre- 
pared that  the  end  curls  over  and  burns  off  as  the  candle  is  consumed, 
thus  making  snuffing  unnecessary ;  *  also,  they  are  often  treated 
with  ammonium  phosphate  or  borate  to  prevent  their  smouldering 
and  emitting  bad  odors  when  the  candle  is  extinguished. 

Paraffine,  ozokerite,  and  sperm  candles  (from  spermaceti)  are 
moulded.  In  order  to  prevent  softening  at  too  low  a  temperature, 
and  to  render  them  less  brittle  when  handled,  a  little  stearic  acid  is 
usually  added. 

The  most  important  candle  stocks  are  palmitic  and  stearic  acids 
and  paraffine  wax. 

*  This  is  accomplished  in  several  ways ;  one  side  of  the  wick  may  be  dipped  in 
size,  or  one  thread  be  drawn  a  little  tighter  than  the  rest. 

380 


CANDLES  381 

Palmitic  and  stearic  acids  are  usually  made  from  tallow  or  palm  oil 
by  saponifying  with  lime,  or  water,  the  hydrolysis  with  the  latter  being 
often  assisted  by  the  addition  of  a  little  acid.  Saponification  with 
lime  is  carried  on  in  two  ways :  (a)  by  boiling  in  open  vessels  with 
about  16  per  cent  of  lime.  The  resulting  insoluble  lime  soap  consists 
of  calcium  oleate,  palmitate,  and  stearate.  It  is  separated  from  the 
lye  and  free  glycerine  which  is  also  formed,  and  is  decomposed  by  treat- 
ment with  sulphuric  acid  and  steam,  setting  free  the  fatty  acid.  (6)  Or 
the  fat  may  be  saponified  by  Milly's  process;  i.e.,  boiled  in  closed 
vessels  called  autoclaves,  under  pressure  of  from  8  to  10  atmospheres, 
with  from  2  to  4  per  Cent  of  lime.  The  latter  probably  merely  starts 
the  hydrolysis,  which  is  finished  by  the  steam  and  water  present.  The 
products  of  the  reaction  are  lime  soap,  free  fatty  acid,  and  glycerine. 
The  turbid  mixture  is  treated  hot  with  just  sufficient  sulphuric  acid 
to  decompose  the  lime  soap.  The  calcium  precipitates  as  sulphate, 
while  on  top  of  the  water  (which  contains  the  glycerine)  is  a  layer  of 
fatty  acid.  This  is  skimmed  off  and  treated  with  water  acidulated 
with  sulphuric  acid  to  insure  complete  decomposition  of  the  lime  soap. 

Twitchell's  process  *  is  one  of  the  more  recent  improvements  in 
saponification  methods.  In  this  a  compound  of  sulphuric  acid  with 
a  fat  acid  (particularly  sulpho-oleic  acid),  and  an  aromatic  body 
with  excess  of  sulphuric  acid,  is  boiled  with  the  oil  or  fat  and  water 
in  a  tank,  until  the  glycerides  are  decomposed.  The  sulpho-fat  acid 
is  called  the  "saponifier,"  and  about  1  to  1}  per  cent  is  added.  The 
mixture  is  thoroughly  stirred  and  steam  blown  in  to  effect  the  boiling, 
the  time  of  which  depends  upon  the  amount  of  saponifier  added; 
with  1  per  cent  from  12  to  24  hours  are  required.  When  saponifica- 
tion is  complete,  the  emulsion  is  broken  by  adding  sulphuric  acid,  or 
a  mixture  of  sodium  carbonate  and  sodium  sulphate;  on  settling, 
the  fatty  acids  come  to  the  top  and  the  glycerine  lye  may  be  drawn 
off  from  below.  With  a  neutral  fat  the  addition  of  some  free  fatty 
acid  is  advisable,  in  order  to  increase  the  solubility  of  the  saponifier 
in  the  fat.  The  process  works  at  low  temperature,  the  fatty  acids 
are  of  good  color,  and  the  yield  is  good.  The  fatty  acids  are  much 
used  for  soap  making,  as  well  as  for  candles ;  the  glycerine  is  refined 
in  the  usual  way  (p..  385). 

The  melted  fatty  acids  obtained  by  any  of  these  processes  are 
run  into  shallow  pans  and  allowed  to  stand  a  few  days  at  a  tempera- 
ture of  about  30°  C.,  when  the  palmitic  and  stearic  acids  crystallize. 
The  magma  is  first  pressed  cold,  and  then  at  40°  C.,  in  bags  in  a  hy- 

*  Wagner's  Jahresbericht,  1900,  548. 


382  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

draulic  press  ;  the  liquid  oleic  acid  separated  forms  the  commercial 
"  red  oil  "  or  "  olein  "  employed  for  soap  stock  ;  the  solid  fatty  acids 
compose  the  candle  stock,  which  is  called  "  stearin."  *  It  melts  at 
52°  to  55°  C.  The  yield  from  tallow  or  palm  oil  is  44  to  48  per  cent 
stearin. 

Saponification  by  water  alone  is  accomplished  by  heating  the  fat 
in  an  autoclave  with  water  to  about  200°  C.  under  pressure  of  about 
15  atmospheres.  A  current  of  superheated  steam  is  introduced,  thus 
thoroughly  mixing  the  contents  of  the  vessel.  The  free  fatty  acid 
and  the  glycerine  both  distil  over  with  the  steam,  the  former  con- 
densing in  the  first  receiver,  while  the  latter  passes  on  to  another. 
This  process  needs  much  care  in  the  regulation  of  the  heat  and  to 
secure  the  complete  decomposition  of  the  glycerides,  but,  when 
properly  worked,  yields  very  pure  products.  The  fatty  acids  are 
chilled  and  pressed  as  above  described,  to  separate  the  olein.  The 
yield  of  stearin  is  about  50  per  cent  from  tallow  or  palm  oil.  Slightly 
rancid  stock  is  more  easily  decomposed  than  neutral  fat. 

By  adding  from  4  to  5  per  cent  of  strong  sulphuric  acid  to  the 
water  in  the  autoclave,  the  hydrolysis  is  accomplished  at  120°  to  150° 
C.  A  part  of  the  glycerine  is  converted  into  glyceryl-sulphuric  acid, 

/OH 
SO2<;  ,  while   some  of   the   oleic   acid,  which  is   an 

\0  -  C3HB(OH)2  xCOOH 

unsaturated  body,  forms  sulpho-stearic  acid,  Ci7H34\  .     By 

X)  •  S03H 

the  action  of  the  water,   this  is  converted  into  hydroxystearic  acid, 
OOH 


/C 
iyHsiC 


si  ,  while  sulphuric  acid  is  regenerated.     The  hvdroxy- 

XOH 

stearic  acid  separates  as  a  solid  with  the  free  stearic  and  palmitic 
acids,  and  in  the  subsequent  purification  of  these  by  distillation  with 
superheated  steam,  it  is  decomposed,  separating  more  water  and  the 
residue  polymerizing  to  form  iso-oleic  acid  .(CigHjjC^),  a  solid,  melting 
at  45°  C.  Thus  the  yield  of  solid  fat  acids  is  slightly  increased,  being 
about  55  per  cent  from  tallow. 

Another  method  of  acid  saponification  consists  in  heating  the  fat 
with  concentrated  sulphuric  acid  for  a  few  minutes  only,  until  the 
cell  walls  of  the  fat  are  destroyed  and  the  hydrolysis  is  begun.  The 
saponification  is  completed  by  boiling  with  water. 

The  mixed  palmitic,  stearic,  and  oleic  acids  are  chilled  and  pressed 

*  Not  to  be  confounded  with  the  glyceride  of  stearic  acid,  p.  350. 


CANDLES  383 

as  already  described.  ,  Saponification  with  acid  gives  a  discolored  prod- 
uct, which  is  usually  purified  by  redistilling  with  superheated  steam. 
The  liquid  "  olein  "  separated  from  the  fatty  acids  by  any  saponi- 
fication  method  is  of  less  value  than  the  solid  acids.  A  process  for 
producing  palmitic  acid  from  this  oleic  acid  is  based  on  the  following 
reaction :  — 

CigHsA  +  2  NaOH  =  Ci6H3iO2  •  Na  +  C2H3O2  •  Na  +  H2. 

Caustic  soda  solution  and  oleic  acid  are  heated  together  in  an  iron 
vessel  provided  with  an  agitator,  until  all  the  water  is  evaporated. 
The  heat  is  then  raised  to  a  little  over  300°  C.,  when  the  evolution 
of  hydrogen  becomes  active.  When  the  hydrogen  ceases  to  escape, 
the  product  is  treated  with  water,  which  dissolves  the  sodium  ace- 
tate and  any  undecomposed  caustic,  leaving  sodium  palmitate  undis- 
solved.  This  is  decomposed  with  sulphuric  acid  to  obtain  the  free 
fatty  acid.  But  the  product  is  too  soft  and  is  an  unsatisfactory 
candle  stock,  hence  the  method  is  not  now  in  use.* 

After  purification,  the  free  fatty  acids,  obtained  by  any  of  the 
processes  above  described,  are  employed  for  candle  stock.  The 
aqueous  solutions  of  glycerine  ("  sweet  waters  "),  resulting  from  the 
saponification,  are  used  in  the  manufacture  of  pure  glycerine. 

*  J.  Soc.  Chem.  Ind.,  1897,  391. 


GLYCERINE 


There  are  two  kind  of  refined  glycerine,  CaH^OFOs,  on  the  market, 
dynamite  glycerine  and  chemically  pure  glycerine.  These  differ  only 
in  color  and  in  the  content  of  pure  glycerine.  It  is  largely  recovered 
from  the  spent  lyes  from  soap  making  and  from  the  "  sweet  waters  " 
from  the  digesters  where  fats  have  been  saponified  with  lime  or  with 
water  under  pressure.*  Much  crude  candle  glycerine  is  imported 
into  this  country  from  Europe,  that  from  France,  Italy,  and  Spain 
being  derived  from  olive  oil. 

Spent  soap  lyes  are  very  dilute  solutions  of  glycerine  and  con- 
tain much  impurity.  The  successful  recovery  of  glycerine  from 
them  is  one  of  the  recent  triumphs  of  chemical  industry.  The  Van 
Ruymbeke  process  is  most  generally  used.  In  this  the  lye  is  set- 
tled and  drawn  off  from  the  sludge.  It  is  then  treated  with  a  spe- 
cial chemical  called  "  persulphate  of  iron,"  the  exact  composition 
of  which  is  not  disclosed,  but  which  contains  about  50  per  cent  of 
sulphuric  acid.  It  is  possibly  a  mixture  of  ferrous  and  ferric  sul- 
phates. This  forms  a  copious  precipitate,  consisting  of  ferric  hydrox- 
ide and  iron  soaps,  which  drags  down  all  other  insoluble  impuri- 
ties. This  precipitate  is  removed  by  filter-pressing  and  the  clear 
liquid  tested  for  any  excess  of  iron  sulphate.  If  any  is  present,  it 
is  exactly  neutralized  with  caustic  soda  and  the  precipitate  filtered 
off.  This  leaves  the  lye  almost  water  white  and  ready  for  the  evapo- 
ration, which  is  done  under  high  vacuum  (27  to  28  inches),  in  a  still, 
across  the  middle  of  which  is  a  steam  chest  having  small  vertical 
tubes.  Fresh  lye  is  introduced,  as  the  evaporation  progresses,  to 
maintain  the  level  of  the  liquid.  A  salt-catch  is  placed  below  the 
steam  chest  in  the  evaporator,  and  in  this  the  salt  and  sodium  sul- 
phate which  separate,  collect,  and  at  the  end  of  the  operation  are 
removed  through  a  door  in  the  front.  The  salt  thus  recovered  is 
sent  to  the  soap  maker,  to  be  used  again  in  salting  out  soap. 

The  vapors  from  the  evaporator  pass  through  a  series  of  "  catch- 
alls  "  to  retain  any  lye,  and  then  go  to  a  wet  vacuum  pump,  which  is 
provided  with  a  jet  condenser.  The  evaporation  is  usually  carried 
on  in  two  or  more  stages  ;  sometimes  it  is  continued  to  a  point  at 
which  sodium  sulphate  will  crystallize,  which  is  thus  removed;  by 
further  evaporation  in  vacuum,  the  common  salt  is  crystallized. 

*  Saponification  with  acid  destroys  much  of  the  glycerine. 
384 


GLYCERINE  385 

When  the  lye  attains  a  density  of  32°  Be.  (1.295  sp.  gr.),  it  con- 
tains about  80  per  cent  of  glycerine,  and  is  called  crude  glycerine. 
This  is  then  distilled  under  a  very  high  vacuum  (28  to  29  inches)  in 
a  still  consisting  of  a  cylindrical  iron  shell  containing  a  closed  steam 
coil  and  a  perforated  pipe,  through  which  superheated  steam  is  intro- 
duced. The  glycerine  in  the  crude  liquid  passes  over  with  the  steam 
into  coolers,  which  are  simply  cast-iron  drums,  cooled  by  the  out- 
side air.  Most  of  the  glycerine  condenses  here,  while  the  uncon- 
densed  steam  and  some  glycerine  passes  on  to  a  surface  condenser. 
The  vacuum  is  maintained  by  a  dry  vacuum  pump.  The  glycerine 
collected  in  the  cooling  drums  is  concentrated  in  vacuum  pans  until 
its  specific  gravity  reaches  1.262.  It  is  then  passed  through  a  filter 
press,  which  removes  any  suspended  dirt,  and  gives  a  clear,  bright 
product.  As  a  rule,  the  glycerine  recovered  from  soap  lye  is  not 
bleached,  and  is  generally  sold  as  dynamite  glycerine. 

Chemically  pure  glycerine  is  made  from  candle  crude  glycerine  by 
a  modification  of  the  Van  Ruymbeke  process.  The  crude  liquid,  hav- 
ing a  density  of  28°  Be.,  is  diluted,  and  treated  with  milk  of  lime  to 
neutralize  any  acid.  It  is  then  treated  with  a  bleaching  material  known 
as  "  black,"  the  composition  of  which  is  kept  secret.  After  filter-press- 
ing, the  glycerine  is  concentrated  to  a  density  of  about  31°  Be.,  in  an 
apparatus  similar  to  that  used  for  dynamite  glycerine.  It  is  then  dis- 
tilled, as  in  the  case  of  the  latter,  and  the  product  condensing  in  the 
coolers  is  thoroughly  bleached  by  treatment  with  more  "  black,"  and 
is  then  filter-pressed.  The  density  of  chemically  pure  glycerine  is  not 
required  to  be  so  high  as  that  of  dynamite  glycerine,  hence  no  final 
concentration  is  necessary.  A  very  fine  grade  of  chemically  pure 
glycerine  is  sometimes  prepared  from  dynamite  glycerine  by  subject- 
ing it  to  the  same  process  employed  for  candle  crude  glycerine. 

Of  the  other  methods  for  recovering  glycerine,  only  the  Glatz 
process  needs  consideration  here.  In  this  the  lye  is  treated  with  a 
small  amount  of  milk  of  lime,  and  then  all  alkali  neutralized  with 
hydrochloric  acid,  and  the  liquid  filter-pressed  to  remove  the  precipi- 
tated matter.  By  evaporating  the  filtrate  under  a  vacuum,  crude 
glycerine  is  obtained,  which  is  distilled  under  low  vacuum  with 
superheated  steam,  the  still  being  heated  by  direct  fire.  The  prod- 
uct is  then  concentrated  in  a  Yaryan  or  similar  evaporator,  until 
heavy  enough  for  market. 

The  yield  of  glycerine  is  always  calculated  on  the  amount  of  fat 
saDonified.     By  careful  work,  6.75  per  cent  of  marketable  glycerine 
can  be  obtained  by  the  Van  Ruymbeke  process. 
2c 


386  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

Glycerine  is  a  thick,  viscid  liquid,  having  a  sweet  taste  and  unc- 
tuous properties.  It  is  soluble  in  water  and  in  alcohol.  High-grade 
dynamite  glycerine  is  of  a  very  pale,  yellow  color,  odorless,  and  free 
from  acids.  It  contains  no  iron,  lead,  or  calcium  salts,  and  only  a 
trace  (0.006  per  cent,  at  most)  of  chlorides.  The  ash  is  not  over 
0.01  per  cent.  The  specific  gravity  should  not  be  less  than  1.262  at 
15°  C.  It  is  chiefly  used  in  making  nitroglycerine;  also  to  some 
extent  as  a  solvent;  in  the  preparation  of  printers'  ink-rolls,  and 
for  increasing  the  body  or  viscosity  of  other  liquids.  Chemically 
pure  glycerine  is  colorless,  containing  less  than  0.009  per  cent  car- 
bonaceous residue,  no  chlorides,  and  leaves  no  ash.  Its  density  is 
about  1.260  sp.  gr.  It  is  largely  used  as  a  preservative  for  tobacco; 
for  confectionery ;  in  pharmacy ;  in  the  preparation  of  cosmetics  ;  as 
a  sweetening  agent  in  fermented  drinks,  and  in  preserves ;  and  owing 
to  its  non-volatile  and  non-drying  character,  as  an  addition  to  inks 
intended  for  rubber  stamps. 

REFERENCES 

Technology  of  Soap  and  Candles.     R.  S.  Christiani,  Philadelphia,  1881. 

Das  Glycerine.     S.  W.  Koppe,  Wien,  1883.     (Hartleben.) 

The  Art  of  Soap  Making.     A.  Watt,  London,  1887. 

Handbuch  der  Seifenfabrikation.     C.  Diete,  Berlin,  1887. 

Guide  pratique  du  Fabricant  de  Savons.     G.  Calmels  and  E.  Saulnier, 

Paris,  1887. 

Traite  pratique  de  Savonnerie.     E.  Morride,  Paris,  1888. 
Manufacture  of  Soaps  and  Candles.     W.  T.  Brannt,  Philadelphia,  1888. 
Seifenfabrikation.     (2  Bander.)     A.  Englehardt,  Wien,  1888. 
Der  praktische  Seifensieder.     H.  Fischer,  Weimar,  1889.     (Voigt.) 
Die  Seifen-Fabrikation.     F.  Wiltner,  Wien,  1891.     (Hartleben.) 
A  Handbook  of  Modern  Explosives.     (Glycerine.)     M.  Eissler,  New  York, 

1890. 

Savons  et  Bougies.     J.  Lefevre,  Paris,  1894. 
Soaps,  Candles,  Lubricators,  and    Glycerine.     W.  L.  Carpenter,  2d  ed., 

London,  1895. 

Soaps  and  Candles.     J.  Cameron,  2d  ed.,  London,  1896.     (Churchill.) 
Manufacture  of  Explosives.     (Glycerine.)     O.  Guttmann,  London,  1896. 
Manufacture  of  Soaps.     G.  H.  Hurst,  1898. 

Soap  Manufacture.     W.  L.  Gadd,  London,  1899.     (Bell  &  Sons.) 
American  Soaps.     H.  Gathman,  2d  ed.,  1899. 
Manufacture  of  Hard  and  Soft  Soaps.     A.  Watts,  1901. 
Textile  Soaps  and  Oils.     G.  H.  Hurst.     1904. 

American  Soaps,  Candles,  and  Glycerine.    L.  L.  Lamborn,  New  York,  1904. 
Die  Gewinnung  und  Verarbeitung  des  Glyzerins.    B.  Lach,  Halle,  a.  S., 

Die  Stearinfabrikation.     Bela  Lach,  Halle,  a.  S.,  1908. 
Journal  of  the  Society  of  Chemical  Industry,  1889,  4.     O.  Hehner. 
American  Chemical  Journal :  17,  59.     Evans  and  Beach. 
Journal  of  Analytical  and  Applied  Chemistry :  — 

IV,  147.    J.  F.  Schnaible.    V,  379.    E.  Twitchell.    VI,  423.    W.  H.  Low. 
Railroad  and  Engineering  Journal :  — 

65,  495  and  551.     C.  B.  Dudley.     67,  199  and  215.     C.  B.  Dudley. 


ESSENTIAL-  OILS 

The  essential  or  volatile  oils  are  liquids  which  give  the  peculiar 
odors  to  plants.  They  occur  already  formed  in  the  plants,  or  are 
produced  by  the  combination  of  substances  in  the  plant,  which  react 
in  the  presence  of  water.  They  have  strong  and  characteristic  odors 
and  pungent  taste,  and  are  generally  volatile  without  decomposition. 
They  are  liquid  at  ordinary  temperatures  and  are  usually  nearly  color- 
less when  fresh,  but  become  darker  and  thick  on  exposure.  Many 
are  optically  active.  They  are  nearly  insoluble  in  water,  but  impart 
their  peculiar  odor  or  taste  to  it.  They  dissolve  in  alcohol,  carbon 
disulphide,  petroleum  ether,  and  fatty  oils.  Excepting  those  con- 
taining organic  ethers,  they  are  not  saponifiable. 

An  essential  oil  is  usually  composed  of  several  chemical  sub- 
stances, all  of  which  are  volatile  with  steam,  and  may  possess  either 
open-  or  closed-chain  molecules.  A  few  oils  consist  almost  wholly  of 
one  constituent.  The  more  important  classes  of  bodies  found  in 
essential  oils  are :  terpenes  of  the  general  formula  CioHi6 ;  camphors, 
oxygenated  substances  of  alcoholic  or  ketone  structure;  geraniol, 
CioHnOH,  and  citronellol,  CioHi9OH,  and  derivatives  of  these,  for 
the  most  part  of  open-chain  structure;  benzene  derivatives,  or  ring- 
form  hydrocarbons,  phenols,  alcohols,  aldehydes,  ketones,  and  acids ; 
aliphatic  bodies,  consisting  of  open-chain  alcohols,  aldehydes,  and 
acids,  or  of  esters  of  these;  sulphides,  thiocyanates,  and  nitrogenous 
bodies  in  a  few  oils.  The  oils  sometimes  contain  resins,  in  solution, 
and  are  then  called  oleo-resins,  or  balsams. 

Some  of  the  essential  oils  can  be  prepared  synthetically ;  some 
are  extracted  from  the  plant  with  solvents,  by  maceration  in  fat,  or 
by  enfleurage,  or  absorption  in  fat.  But  most  commercially  impor- 
tant essential  oils  are  obtained  by  distillation  with  water  or  steam 
or  by  pressing. 

In  the  distillation  process,  the  oil-bearing  material  is  put  into  a 
still  with  a  considerable  quantity  of  water,  which  is  then  brought  to. 
boiling.  The  steam  carries  the  oil  into  the  condenser  mechanically, 
where  a  mixture  of  oil  and  water  is  obtained,  which  is  usually  milky 
at  first.  On  standing,  it  separates  into  two  distinct  layers,  the  oil 
usually,  but  not  always,  on  top.  The  water  is  drawn  off,  and  re- 
turned to  the  still  with  the  new  charge ;  or  the  receiver  is  so  arranged 
that  the  water  returns  continuously  to  the  still  through  a  siphon. 

387 


388  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

When  extraction  is  employed,  alcohol,  carbon  disulphide,  ether, 
or  petroleum  naphtha  may  be  used.  The  solvent  is  evaporated  from 
the  oil,  and  recovered. 

Some  oils,  especially  those  of  lemon  and  orange,  are  obtained  by 
the  use  of  hydraulic  or  screw  presses.  The  product  is  fragrant,  but 
rather  deeply  colored. 

Maceration  in  fat  is  employed  for  some  essences  which  are  in- 
jured by  high  temperatures.  The  fat  used  is  a  perfectly  pure  and 
sweet  lard,  tallow,  or  heavy  paraffine  oil  which  is  melted  in  a  water 
bath.  The  flowers  or  leaves  are  stirred  in  and  digested  until  ex- 
hausted. The  fat  takes  up  the  essential  oil  and  is  treated  with  alco- 
hol, which  extracts  part  of  the  essence.  These  alcoholic  solutions 
are  much  used  in  perfumery;  the  fat,  still  containing  some  of  the 
essential  oil,  is  used  for  pomades  and  similar  purposes. 

Enfleurage  is  employed  for  those  very  delicate  oils  whose  odors 
are  destroyed  by  even  moderate  heat.  The  flowers  to  be  extracted 
are  Jaid  in  a  wooden  frame  on  the  glass  bottom  of  which  a  thin  layer 
of  perfectly  neutral  fat  is  spread.  A  number  of  frames  are  placed 
in  a  pile  and  allowed  to  stand  for  some  hours,  when  the  flowers  are 
replaced  by  fresh  ones.  This  is  repeated  until  the  fat  has  become 
strongly  charged  with  the  perfume. 

Oil  of  turpentine  or  spirits  of  turpentine  is  derived  from  conifer- 
ous trees,  especially  from  the  pine,  Pinus  palustris,  Mill.,  and  P. 
tceda,  L.,  and  from  the  Scotch  fir,  P.  sylvestris,  L.  The  trees  are 
"  boxed/'  i.e.  a  cavity  is  cut  near  the  root,  and  the  bark  channelled 
with  shallow  cuts  which  lead  down  to  the  box.  The  crude  turpen- 
tine (an  oleo-resin)  flows  from  the  cuts  and  collects  in  the  box,  from 
which  it  is  dipped  out  at  intervals.  It  forms  an  exceedingly  sticky, 
viscid  liquid  balsam  which  is  distilled  with  steam.  The  volatile  oil 
of  turpentine  (about  17  per  cent)  passes  over  with  the  steam,  while 
a  residue  of  resin  (rosin  or  colophony)  remains  in  the  still. 

The  oils  obtained  from  different  varieties  of  coniferce  differ  some- 
what in  their  properties.  Three  commercial  grades  are  important: 
(a)  French  turpentine  consisting  chiefly  of  a  terpene,  CioHie,  and 
called  terebenthene  or  laewpinene,  which  has  a  Isevo-rotary  action  on 
polarized  light  rays ;  (b)  American  or  English  turpentine  consisting 
of  a  terpene,  CioHie,  called  australene,  which  has  the  same  specific 
gravity,  boiling  point,  and  chemical  properties  as  terebenthene,  but 
is  dextro-rotary ;  (c)  Russian  turpentine  which  contains  the  terpene, 
sylvestrine,  and  some  of  a  pinene  resembling  australene.  The  oil  first 
distilled  is  usually  washed  with  caustic  soda  solution  to  saponify 


ESSENTIAL   OILS  389 

rosin  acids,  and  is  then  redistilled  for  "  rectified  spirits  of  turpen- 
tine." Commercial  oil  of  turpentine  or  "  turps  "  is  a  water-white, 
mobile,  refractive  liquid  of  0.640  to  0.872  sp.  gr.,  distilling  between 
156°  and  170°  C.  It  is  insoluble  in  water  and  in  glycerol,  but  solu- 
ble in  ether,  absolute  alcohol,  carbon  disulphide,  chloroform,  benzene, 
fatty  and  essential  oils.  It  dissolves  sulphur,  phosphorus,  wax,  caout- 
chouc, and  resins,  and  is  used  as  a  solvent  in  varnishes  and  paints. 
It  burns  with  a  smoky  flame.  It  absorbs  oxygen  from  the  air,  be- 
coming resinous.  According  to  Kingzett,  oxidation  of  turpentine 
forms  camphoric  peroxide,  CioHi4O4,  which  with  water  yields  cam- 
phoric acid  and  hydrogen  peroxide.  By  passing  air  into  Russian 
turpentine  in  the  presence  of  warm  water,  the  disinfectant  "  sanitas  " 
is  made. 

Turpentine  is  now  largely  produced  by  the  destructive  distilla- 
tion of  resinous  pine  wood,  often  with  the  aid  of  steam  injected  into 
the  retort ;  acetic  acid  and  wood  alcohol  are  by-products. 

Camphor,*  doHi6O,  is  an  oxygenated  essential  body  (probably  a 
ketone)  occurring  in  some  crude  volatile  oils.  Commercially  it  is 
obtained  from  the  wood  of  the  camphor  laurel,  Cinnamomum  Cam- 
phor a,  Nees  &  Eberm.,  native  in  Japan  and  Borneo.  The  trunk  and 
branches  of  the  tree  are  roughly  distilled  with  water,  and  the  crude 
camphor  purified  by  sublimation. 

Artificial  camphor  may  be  made  in  several  ways,f  by  oxidizing 
borneol  or  isoborneol  with  permanganate,  ozone,  oxygen,  air,  chlorine, 
or  nitrous  gases.  Catalytic  reagents  may  be  used  to  accelerate  the 
reaction,  as  when  the  vapors  of  isoborneol  and  air  or  oxygen  are 
passed  over  platinized  asbestos,  metallic  copper,  or  bits  of  earthen- 
ware at  175°  to  180°  C.,  thus  producing  a  mixture  of  camphor,  cam- 
phene,  and  isoborneol,  from  which  the  camphor  is  separated.  Or 
isoborneol  dissolved  in  benzene  is  treated  with  chlorine ;  camphor  is 
produced  and  remains  dissolved  in  the  benzene  from  which  it  is 
crystallized.  The  reaction  is  CioHisO  +  2  Cl  =  2  HC1  +  Ci0Hi6O. 

Isoborneol  Camphor 

Camphor  is  a  white,  translucent  body  having  a  penetrating  odor 
and  pungent  taste ;  it  melts  at  175°  C.,  boils  at  204°  C.,  is  volatile  at 
ordinary  temperatures,  and  burns  with  a  luminous  smoky  flame.  Its 
specific  gravity  is  0.986  to  0.996.  It  is  slightly  soluble  in  water, 
easily  so  in  alcohol,  ether,  chloroform,  carbon  disulphide,  acetone,  and 
essential  oils.  It  is  largely  used  in  the  manufacture  of  celluloid 

*  J.  Soc.  Chem.  Ind.,  1884  (3),  353. 

t  Ibid.,  1904,  75,  881 ;  1905,  249,  857,  902,  1188.  U.  S.  Pats.,  770940,  790601, 
801483,  801485,  802792,  802793. 


390  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

(p.  584),  in  explosives,  in  medicine,  and  pharmacy,  and  as  a  protec- 
tive against  the  ravages  of  insects. 

Thymol,  CioHi3  •  OH,  is  a  phenol  occurring  in  the  oil  of  thyme 
and  in  some  other  volatile  oils.  It  is  similar  to  carbolic  acid  in  its 
character,  and  it  is  obtained  by  washing  the  crude  oil  with  caustic 
soda,  the  alkaline  solution  of  thymol  being  separated  and  decom- 
posed with  mineral  acid ;  or  the  oil  is  chilled  and  the  thymol  crys- 
tallizes and  may  be  filtered  out. 

It  is  a  colorless  crystalline  body,  having  a  specific  gravity  of 
1.028,  and  melting  at  44°  C.  It  is  very  slightly  soluble  in  water, 
but  readily  so  in  alcohol,  glacial  acetic  acid,  ether,  etc.  It  is  a  pow- 
erful antiseptic,  and  is  much  used  in  medicine  and  in  pharmacy. 

Menthol,  CioHig  •  OH,  is  an  alcohol  occurring  in  oil  of  pepper- 
mint, and  which  crystallizes  when  the  oil  is  chilled.  It  is  a  white 
solid,  very  sparingly  soluble  in  water,  but  readily  so  in  ether,  alco- 
hol, and  fixed  and  volatile  oils.  It  does  not  combine  with  caustic 
alkalies.  It  melts  at  41°  to  43°  C.  It  is  much  used  as  a  remedy  for 
neuralgic  pains  and  headache. 

The  essential  oil  of  almonds  is  produced  by  the  action  of  emulsin, 
a  nitrogenous  ferment  upon  amygdalin,  a  glucoside.  To  obtain  it, 
the  marc  of  almond  kernels  left  after  pressing  for  the  fixed  oil  is 
distilled  with  water.  It  contains  benzaldehyde,  with  some  hydrocyanic 
acid  and  other  nitrils.  It  is  purified  by  redistillation  over  a  mixture 
of  lime  and  ferrous  sulphate.  It  is  readily  oxidized  on  exposure  to 
the  air,  forming  benzoic  acid.  Artificial  almond  essence  is  made  by 
boiling  benzal  chloride  with  lead  nitrate  or  calcium  carbonate  and 
water.  This  oil  is  used  in  making  dyes  and  as  a  flavoring  extract. 

Nitrobenzene  is  used  under  the  name  "  mirbane"  as  a  substitute 
for  almond  essence  for  scenting  soaps. 

Oil  of  bergamot  is  prepared  from  the  fruit  of  a  species  of  orange, 
Citrus  Bergamia,  Risso,  by  hand  pressing  or  distillation  with  water. 
It  is  a  light  green,  pleasant-smelling  oil,  containing  a  large  amount 
of  a  terpene,  citrene,  CioHie,  boiling  at  175°  to  177°  C.  It  is  chiefly 
used  in  perfumery. 

Oil  of  Cajaput,  prepared  from  the  leaves  of  Melaleuca  Leucaden- 
dron,  L.,  is  a  green  liquid  of  peculiar  odor,  distilling  at  170°  to  180°  C. 

Cedar  oil  is  obtained  by  distilling  the  wood  of  red  cedar,  Juni- 
perus  Virginiana,  L.,  with  water.  It  contains  a  mixture  of  cedrene, 
CisHjn,  and  a  camphor-like  body,  Ci5H26O. 

Chamomile  oil,  distilled  from  Anthemis  nobilis,  L.,  consists  of 
isobutyl  and  amyl  esters  of  angelica  and  tiglic  acids. 


ESSENTIAL   OILS  391 

Cinnamon  oil  or  oil  of  cassia  is  distilled  from  the  inner  bark  of 
Cinnamomum  Zeylanicum,  Nees.  It  is  a  yellow  oil,  consisting  mainly 
of  cinnamic  aldehyde,  with  a  little  cinnamic  acid.  It  is  slightly 
heavier  than  water. 

Oil  of  cloves  is  obtained  by  distilling  cloves  (the  flower  buds  of 
Eugenia  caryophyllata,  Thunb.)  with  water.  It  is  a  mixture  of  a  ter- 
pene,  Ci5H24  (boiling  at  251°  C.),  and  eugenol,  CioHi2O2.  It  is  yellow, 
of  a  penetrating  odor,  and  heavier  than  water. 

Eucalyptus  oil,  distilled  from  the  leaves  of  several  Australian 
trees,  Eucalyptus  Globulus,  Labill.,  and  others,  is  used  in  perfumery, 
in  medicine,  and  in  scenting  soaps.  It  contains  terpenes  (especially 
pinene,  doHi6),  cymene,  and  eucalyptol  or  cineol,  CioHi8O. 

Geranium  oil  is  distilled  from  the  leaves  of  Pelargonium  Radula, 
L'Herit.  Its  odor  resembles  that  of  rose  oil,  which  it  is  chiefly  used 
to  adulterate. 

Lavender  oil  is  distilled  from  the  flowers  of  Lavandula  vera,  D.  C. 
It  has  little  odor  when  first  prepared,  the  perfume  being  developed 
by  exposure  to  the  air.  Oil  of  spike  is  obtained  from  L.  Spica,  Cav. 
It  is  similar  to  lavender  oil  and  is  used  in  porcelain  painting. 

Oil  of  lemon  is  expressed  from  the  rind  of  the  fruit  of  Citrus  Li- 
monum,  Risso.  Poor  grades  are  made  by  distilling  the  rind.  The 
oil  contains  a  terpene  (limonene),  CioHie,  boiling  at  176°  C.  It  is 
chiefly  used  in  perfumery,  and  as  a  flavoring  essence  in  confectionery. 

Mustard  oil  is  distilled  from  the  seeds  of  Brassica  nigra,  Koch., 
after  the  fixed  oil  has  been  removed  by  pressing.  It  contains  nitro- 
gen and  sulphur,  and  its  essential  principle  is  allyl  thiocarbamide, 
CsH5N :  CS.  It  is  a  pale  yellow  oil  of  1.015  to  1.025  sp.  gr.,  boiling 
at  148°  C.,  and  having  a  pungent,  disagreeable  odor.  It  is  a  power- 
ful irritant  and  produces  blisters  on  the  skin.  It  is  not  present  in 
dry  seeds,  but  is  formed  by  the  action  of  a  ferment,  myrosin,  upon  a 
glucoside,  potassium  myronate,  in  the  presence  of  water.  Artificial 
mustard  oil  is  prepared  by  distilling  allyl  iodide  with  potassium  thio- 
anate :  — 

C3H5I  +  KSNC  =  KI  +  C3H5  •  N :  CS. 

il  of  peppermint,  obtained  by  distilling  the  herb  Mentha  piperita, 
L.,  is  a  colorless  or  greenish  yellow  liquid,  of  strong  pungent  taste 
and  odor,  having  a  specific  gravity  of  0.900  to  0.920.  It  is  a  mix- 
ture of  menthol,  Ci0Hi9  •  OH,  with  several  terpenes.  It  is  much 
used  in  medicine  and  as  a  flavoring  essence. 

Attar  of  roses  is  obtained  by  distilling  the  flowers  of  various  species 
of  rose.  It  is  a  pale  yellowish  liquid,  somewhat  lighter  than  water,  hav- 


392  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

ing  a  very  delicate,  rich  odor.  It  crystallizes  at  ordinary  temperatures 
and  deposits  an  inodorous  body  resembling  paraffine.  The  constitu- 
tion of  the  oil  is  not  known.  Owing  to  its  high  price,  it  is  frequently 
adulterated  with  geranium  oil,  which  resembles  it  somewhat  in  odor. 

Oil  of  rue  is  distilled  from  the  herb  Ruta  graveolens,  L.  It  con- 
sists mainly  of  methyl  nonylketone,  CgHi9  •  CO  •  CHs. 

Oil  of  sassafras  is  distilled  from  the  root  of  Sassafras  officinale, 
Nees  &  Ebern.  It  contains  safrol,  Ci0Hi0O2,  and  some  pinene,  Ci0Hi6. 
Safrol  melts  at  8°  C.  and  boils  at  228°  to  235°  C.  Sassafras  oil  is 
much  used  for  flavoring. 

Oil  of  thyme  or  origanum  is  derived  from  the  leaves  and  flowers 
of  Thymus  vulgaris,  L.  It  is  yellowish  red,  has  a  pungent  taste, 
and  a  specific  gravity  of  0.900  to  0.930.  It  contains  a  Isevo-pinene, 
CioHie,  boiling  at  160°  C. ;  thymol,  CioH]4O,  and  cymene,  Ci0Hi5, 
boiling  at  175°  C. 

Oil  of  wormwood  is  distilled  from  the  herb  Artemisia  Absinthium,  L. 

Oil  of  wintergreen  is  distilled  from  the  leaves  of  Gaultheria  pro- 
cumbens,  L.  It  contains  methyl  salicylate,  C6H4  •  (OH)  •  COO  •  CH3, 
with  a  little  terpene.  It  is  a  liquid  of  pleasant  smell  and  taste, 
boiling  at  218°  C.,  and  of  1.175  to  1.185  sp.  gr.  at  15°  C.  It  rotates 
the  plane  of  polarization  to  the  left.  It  is  used  as  a  flavoring  essence. 

An  artificial  oil  is  made  by  heating  salicylic  acid  with  oil  of  vitriol 
and  methyl  alcohol. 

REFERENCES 

Treatise  on  the  Manufacture  of  Perfumes.     J.  H.  Snively,  New  York,  1890. 
Die  fliichtigen  Oele  des  Pflanzenreiches.     G.  Bornemann,  Weimar,  1891. 
Handbuch  der  Parfumerie-  und  Toilettenseifen-fabrikation.     C.   Deite, 

Berlin,  1891.     (J.  Springer.) 

The  Art  of  Perfumery.     C.  H.  Piesse,  London,  1891.     5th  ed. 
Treatise  on  the  Manufacture  of  Perfumery.     W.  T.  Brannt,  Phila.,  1902. 
Odorographia ;  a  Natural  History  of  Raw  Materials  and  Drugs  used  in  the 

Perfume  Industry.    J.  C.  Sawer,  London,  1892,  Part  I.     1894,  Part  II. 
Perfumes  and  their  Preparation.     Askinson-Furst,  London,  1892. 
Fabrication  des  Essences  et  des  Parfums.     P.  Durvelle,  Paris,  1893. 
Descriptive  Catalogue  of  Essential  Oils  and  Organic  Chemical  Prepara- 
tions.    F.  B.  Power,  New  York,  1894.     (Fritsche  Bros.) 
Die  Riechstoffe  u.  Ihre  Verwendung.     St.  Mierzinski,  Weimar,  1894. 
Aether  und  Grundessenzen.     Theodor  Horatius,  Leipzig,  1895. 
Semi-Annual   Reports.     1892+.     Schimmel   and   Co.    (Fritsche   Bi 

Leipzig  and  New  York. 
Huiles  essentielles  et  leurs  principaux  constituants.     Charabot,  Dupont 

et  Fillet,  Paris,  1899. 
Chemistry  of  Essential  Oils  and  Artificial  Perfumes.     E.  J.  Parry,  New 

York,  1900. 

Die  Aetherischen  Oele.     F.  W.  Semmler,  Leipzig,  1906. 
Die  Aetherischen  Oele.     Gildemeister  und  Hoffmann,  Berlin,  1910. 
The  Volatile  Oils.     E.  Gildemeister  and  F.  Hoffmann.     Translated  by 

Edward  Kremers.     New  York,  1914. 


jj-f  CtJ.  Ct~ 


RESINS  AND  GUMS 

Resins  are  oxygenated  bodies,  generally  produced  by  the  oxida- 
tion of  terpenes  or  related  hydrocarbons  in  plants  or  in  essential 
oils.  They  are  found  as  natural  or  induced  exudations  from  plants, 
often  mixed  with  the  essential  oil,  forming  oleo-resin  or  balsam,  or 
with  mucilaginous  matter,  forming  gum-resin.  True  resins  are  com- 
pact masses,  insoluble  in  water,  devoid  of  marked  taste  or  odor,  and 
usually  composed  of  substances  of  an  anhydric  or  acid  nature.  They 
are  nearly  all  soluble  in  alcohol,  ether,  benzene,  and  in  most  vola- 
tile oils,  and  may  usually  be  saponified  with  caustic  alkali.  When 
heated,  they  soften  below  their  melting  points,  but  cannot  be  dis- 
tilled undecomposed.  The  chief  uses  of  resins  are :  in  making  var- 
nish ;  for  soap ;  as  a  constituent  of  sealing  wax ;  in  medicine,  and  in 
sizing  paper  and  cloth. 

Common  rosin,  or  colophony,  is  a  resin  obtained  by  the  distilla- 
tion of  turpentine  oil  from  crude  turpentine  (p.  388).  Three  grades 
of  rosin  are  in  the  market,  —  "  virgin,"  yellow  dip,  and  hard.  Virgin 
rosin  is  made  from  the  first  turpentine  that  exudes  after  the  tree  is 
"  boxed."  It  is  of  a  very  light  yellow  or  amber  color.  The  greater 
part  of  the  crude  turpentine  furnishes  yellow  dip.  The  hard  is  made 
from  the  scrapings  from  the  tree  after  the  turpentine  has  become 
too  thick  to  run  into  the  box ;  it  is  very  dark,  being  nearly  black. 

Rosin  is  brittle,  melts  at  100°  to  140°  G.,  and  has  a  specific 
gravity  of  about  1.08.  It  contains  a  large  amount  of  abietic  anhy- 
dride, C44He2O4,  which  is  readily  converted  into  abietic  acid,  C^H^Os. 
Rosin  is  converted  by  alkalies  into  "  rosin  soap  "  (p.  373),  which  is 
deliquescent  and  very  soluble  in  water.  Rosin  is  used  as  a  constitu- 
ent of  laundry  soaps ;  as  an  addition  to  cheap  varnishes ;  as  a  flux 
in  soldering  and  brazing  metals ;  in  pharmacy ;  in  ship  calking ;  and 
as  an  adulterant  of  fats,  waxes,  and  mineral  oils. 

Rosin  must  not  be  confounded  with  wood-tar,  or  pitch,  obtained 
by  the  destructive  distillation  of  wood. 

Rosin  may  be  distilled  in  vacua,  or  by  the  aid  of  superheated 
steam,  with  very  little  decomposition ;  but  when  heated  in  a  retort, 
it  yields  decomposition  products  consisting  of  gases,  liquids,  and 
pitch.  The  liquid  distillate  is  composed  mainly  of  "  rosin  spirit,"  *  a 
very  complex  body,  boiling  below  360°  C.  (resembling  oil  of  turpen- 

*  Renard.     J.  Chem.  Soc.,  46,  843. 
393 


394  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

tine,  for  which  it  is  sometimes  substituted),  and  "  rosin  oil,"  *  a  heav- 
ier liquid,  boiling  above  360°  C. 

The  rosin  oil  is  purified  by  treatment  with  a  little  sulphuric  acid, 
followed  by  lime  water,  and  then  redistilled,  sometimes  with  caustic 
soda  in  the  still.  It  has  a  specific  gravity  of  0.980  to  1.110  ;  is  water 
white  to  brown  in  color,  and  is  only  slightly  soluble  in  alcohol,  but 
easily  dissolved  in  fatty  oils,  ether,  chloroform,  etc.  It  is  nearly 
odorless,  and  has  a  strong,  peculiar  taste.  It  is  not  subject  to  true 
saponification,  although  when  treated  with  milk  of  lime,  a  combina- 
tion between  the  terpenes  of  the  oil  and  the  calcium  hydroxide  takes 
place,  forming  a  solid  mass.  This  is  stirred  up  with  more  rosin  oil, 
to  form  a  soft  mixture  of  about  the  proportions,  13  CioHi6  •  Ca(OH)2, 
which  is  the  commercial  "  rosin  grease/'  used  as  a  lubricant  on  iron 
bearings.  Rosin  oil  is  largely  used  in  making  such  lubricants,  and 
as  an  adulterant  for  olive  and  boiled  linseed  oils. 

Burgundy  pitch  is  a  resin  resembling  common  rosin,  but  obtained 
from  the  Norway  spruce,  Picea  excelsa,  Link.  The  trees  are  scari- 
fied, and  the  resin  allowed  to  harden,  when  it  is  collected  and  treated 
with  boiling  water,  to  remove  the  volatile  oils.  Its  chief  constituent 
is  abietic  anhydride.  When  stirred  up  with  fats  and  water,  melted 
rosin  forms  a  mass  resembling  Burgundy  pitch  in  its  opacity  and 
other  properties. 

Mastic  and  Sandarac  are  somewhat  similar  resins,  obtained  from 
evergreen  shrubs  which  grow  along  the  shores  of  the  Mediterranean 
Sea,  especially  on  the  island  of  Chios,  and  in  northern  Africa.  The 
former,  derived  from  Pistacia  Lentiscus,  L.,  occurs  in  commerce  as 
small  translucent  grains,  or  "  tears,"  which  soften  when  masticated, 
and  have  a  slightly  bitter,  aromatic  taste.  It  is  soluble  in  acetone, 
alcohol,  and  turpentine  oil,  and  is  used  in  varnish  making  and  in 
pharmacy. 

Sandarac,  also  called  "  gum  jumper,"  is  obtained  from  Callitris 
quadrivalvis,  Vent.,  an  evergreen  growing  in  northern  Africa.  It  is 
used  in  varnishes. 

Amber  is  a  fossil  resin  found  along  the  coast  of  the  Baltic  Sea,  in 
Germany.  It  is  the  hardest  and  heaviest  of  all  resins,  is  capable  of 
taking  a  high  polish,  and  is  insoluble  in  most  of  the  ordinary  sol- 
vents. Its  color  varies  from  very  light  yellow  to  deep  brownish  red. 
It  often  contains  perfect  specimens  of  fossil  insects.  When  heated 
above  its  melting  point,  it  is  partly  decomposed,  and  then  becomes 
soluble  in  alcohol  and  in  oil  of  turpentine. 

*  Renard.     J.  Chem.  Soc.,  24,  304,  1175. 


RESINS   AND    GUMS  395 

Transparent  pieces  of  amber  are  much  prized  for  jewelry,  fancy 
articles,  mouth-pieces  for  pipes  and  cigar  holders,  and  for  other  orna- 
mental purposes.  It  is  also  used  in  preparing  a  fine  transparent 
varnish  for  use  on  negatives  in  photography. 

When  subjected  to  destructive  distillation,  amber  yields  a  gas,  an 
organic  acid  (succinic  acid),  and  an  oil  called  "  oil  of  amber."  This 
oil  and  the  acid  are  used  somewhat  in  pharmacy.  By  treating  oil  of 
amber  with  fuming  nitric  acid,  a  substance  resembling  musk  in  odor 
and  other  properties  is  obtained.* 

Copal  is  a  valuable  resin.  Soft  copal,  soluble  in  ether,  is  obtained 
from  living  trees  in  Java,  Sumatra,  the  Philippine  Islands,  Australia, 
and  New  Zealand.  The  better  quality,  hard  copal,  is  a  fossil  gum, 
found  in  irregular  lumps,  buried  in  the  earth,  in  the  East  Indies, 
Madagascar,  West  Africa,  and  South  America,  the  last  variety  being 
called  gum  animi.  Hard  copal  varies  in  color  from  pale  yellow  to 
brown.  Its  specific  gravity  is  usually  1.059  to  1.072.  It  has  a  higher 
melting  point  than  soft  copal,  and  is  insoluble  in  ether  or  volatile 
oils.  But  by  heating  above  its  melting  point,  a  partial  decomposition 
takes  place,  and  the  resin  is  rendered  more  soluble  in  these  solvents. 

Hard  copal  is  the  hardest  of  all  resins,  except  amber,  and  is  most 
valuable  for  varnish  making.  For  this  it  must  first  be  melted,  or 
"run,"  and  while  in  the  liquid  state,  hot  oil  of  turpentine  is  slowly 
added  and  mixed  with  it. 

Dammar  is  obtained  from  a  coniferous  tree,  Agathis  loranthifolia, 
Salisb.,  in  the  Moluccas.  The  resin  exudes  from  the  tree  in  drops, 
and  is  collected  after  it  dries.  It  is  soluble  in  essential  and  in  fixed 
oils,  in  crude  benzene,  and  partially  so  in  alcohol  and  ether.  It  is 
very  light  colored,  and  makes  a  transparent  varnish. 

Kauri,  or  Australian  dammar,  is  obtained  from  a  New  Zealand 
tree,  Agathis  australis,  Stend.  Much  of  the  kauri  of  trade  is  a  fossil 
resin,  and  is  somewhat  darker  colored  than  the  true  dammar  and 
copal.  It  is  extensively  used  for  varnish  making,  being-  cheaper 
than  copal. 

Dragon's  blood  is  a  deep  crimson  red  resin,  which  exudes  from 
the  fruit  of  a  palm  tree,  Dcemonorops  Draco,  Blume.,  indigenous  in 
the  East  Indies.  It  is  collected  by  the  natives  and  made  into  irregu- 
lar lumps,  or  cast  into  long  sticks  in  moulds  made  by  rolling  palm 
leaves  into  cylinders  and  closing  one  end.  It  is  freely  soluble  in 

*  The  artificial  musk  of  commerce  is  now  made  from  butyl  toluene,  by  the  action 
of  nitric  and  sulphuric  acids.  Bauer.  Berichte  der  deutschen  chemischen  Gesell- 
schaft,  24,  2832. 


396  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

nearly  all  of  the  ordinary  solvents,  except  petroleum  ether,  oil  of 
turpentine,  and  ether.  It  is  slightly  soluble  in  the  two  latter.  It  is 
used  in  pharmacy,  and  in  certain  colored  varnishes. 

Guaiacum  is  a  resin  derived  from  certain  West  Indian  trees, 
especially  Guaiacum  sanctum,  L.,  and  G.  officinale,  L.  It  exudes  from 
the  trees  through  incisions,  and  forms  "  tears  "  or  lumps  which  are 
sent  to  market.  It  is  soluble  in  ether,  alcohol,  chloroform,  acetone, 
and  caustic  soda.  Its  alcoholic  solution  is  employed  as  a  reagent 
for  oxidizing  substances,  with  which  it  shows  a  blue  color,  which  is 
destroyed  by  reducing  agents,  but  reappears  when  again  oxidized. 
Hydrogen  peroxide,  however,  does  not  change  the  color  to  blue  unless 
in  the  presence  of  blood.  Hence  guaiacum  in  alcohol,  with  hydrogen 
peroxide,  is  used  as  a  reagent  for  detecting  blood  stains.  Guaiacum 
is  also  used  in  medicine  in  treating  rheumatism  and  gout. 

Lac  is  a  resin  produced  by  the  bite  or  sting  of  certain  insects, 
Coccus  lacca,  Kerr,  on  the  small  twigs  of  several  species  of  East  In- 
dian trees,  of  which  Ficus  Indica,  L.,  and  F.  religiosa,  L.,  are  the 
chief.  The  resin  appears  to  be  formed  from  the  plant  sap  by  the 
female  insect,  from  whose  body  it  exudes,  ultimately  burying  .the 
insect  and  her  eggs,  and  forming  a  thick  excrescence  on  the  twigs. 
It  is  collected,  together  with  the  twigs  which  it  envelops,  and  is 
brought  into  commerce  as  "  stick  lac."  The  insect  also  secretes  a 
brilliant  red  dye  which  is  extracted  by  macerating  the  crude  lac  in 
warm  water.  The  aqueous  solution  is  evaporated  to  dryness,  and  the 
residue  sold  as  lac-dye.  After  the  dye  is  extracted,  the  resin  is 
known  as  "  seed  lac."  This  is  refined  by  carefully  melting  and  strain- 
ing through  muslin  bags  to  remove  foreign  matter.  The  melted 
lac  is  then  poured  in  thin  films  over  cold  porcelain,  copper,  or  wood 
cylinders,  or  plates,  and  allowed  to  cool,  when  it  hardens  and  scales 
off  in  thin  flakes,  and  is  called  "  shellac."  Or  it  is  poured  into  moulds 
to  form  "  button,"  or  "  garnet  lac."  The  shellac  is  the  better  quality, 
and  is  of  a  pale  orange,  or  red  color,  and  is  nearly  transparent.  It  is 
used  for  spirit  varnish. 

Lac  is  partially  soluble  in  strong  alcohol,  forming  a  turbid,  gummy 
liquid  much  used  as  a  varnish  and  wood  filler.  It  is  partly  soluble 
in  ether,  chloroform,  and  turpentine,  but  is  completely  dissolved  by 
caustic  alkalies  and  borax  solutions.  Such  solutions  are  used  as 
water  varnishes.  Lac  is  also  used  as  the  basis  of  the  better  grades 
of  sealing  wax. 

Bleached  shellac  is  made  by  the  action  of  sodium  hypochlorite  on 
an  alkaline  solution  of  lac ;  the  lac,  precipitated  with  acid,  is  melted 


RESINS   AND   GUMS  397 

under  water  and  "  pulled  "  to  make  it  white  and  fibrous.  It  is  used 
for  white  varnishes,  but  becomes  insoluble  in  alcohol  after  some  time. 
Elemi  is  a  resin  obtained  from  certain  trees,  Canarium  commune, 
L.,  in  the  Philippine  Islands,  Canarium  Mauritianum,  Blume.,  in 
Mauritius,  Amyris  elemifera  in  Mexico,  and  from  several  varieties  of 
Idea  in  Brazil.  The  resin  varies  from  white  to  gray  in  color,  and  is 
soft  and  tough.  It  softens  at  75°  C.,  and  melts  completely  at  120°  C. 
It  is  soluble  in  alcohol  and  other  solvents,  and  is  used  chiefly  to  give 
toughness  to  varnishes  made  from  harder  resins. 

VARNISHES 

The  resins  are  chiefly  important  as  furnishing  the  material  for 
varnish  making.  A  varnish  is  a  solution  of  a  resin,  or  of  a  drying 
oil,  which,  when  "exposed  to  the  air,  becomes  hard  and  impervious  to 
air  and  moisture,  through  evaporation  of  the  solvent  or  oxidation  of 
the  oil.  Three  classes  of  varnishes  are  important :  (1)  Spirit  var- 
nishes, consisting  of  resin  dissolved  in  alcohol,  petroleum  spirit, 
acetone,  or  in  any  other  volatile  solvent;  (2)  turpentine  varnishes, 
in  which  the  resin  is  dissolved  in  oil  of  turpentine ;  and  (3)  linseed 
oil  varnishes,  which  may  consist  of  linseed  oil  alone,  or  with  the 
addition  of  resin  and  turpentine  oil. 

Spirit  varnish  dries  rapidly,  leaving  the  resin  as  a  thin  and  bril- 
liant film  on  the  surface  to  which  it  is  applied.  This  film  is  brittle, 
and  liable  to  crack  and  scale  off.  The  addition  of  turpentine  overcomes 
this  difficulty  to  some  extent.  Spirit  varnishes  are  often  colored  with 
dyes  soluble  in  alcohol,  or  with  dragon's  blood,  gamboge,  or  cochineal. 
The  most  important  spirit  varnishes  are  made  with  shellac,  though 
mastic,  sandarac,  and  dammar  are  used. 

Turpentine  varnish  is  tough  and  flexible,  but  much  slower  in  drying 
than  the  spirit  varnishes.  The  resin  is  simply  dissolved  in  the  hot 
oil,  and  after  cooling  is  ready  for  use. 

Linseed  oil  varnishes  are  the  most  important.  If  well-boiled  oil 
(p.  357)  is  applied  to  a  surface,  it  dries  to  a  hard  film,  but  without 
much  brilliancy  of  surface.  By  dissolving  a  resin  in  the  boiled  oil 
and  thinning  to  the  proper  consistency  with  turpentine,  a  varnish 
is  obtained  which  dries  with  a  hard,  glossy  surface,  impervious  to 
air  and  moisture.  The  resins  used  are  mainly  amber,  copal,  anime, 
kauri,  and  dammar,  for  transparent  varnish.  The  hard  resins  are 
not  directly  soluble  in  the  oil,  but  must  first  be  partly  decomposed 
or  "  run,"  by  heating  above  their  melting  points.  There  is  consider- 
able evolution  of  irritating  gases  during  this  fusion,  and  an  oily 


398  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

distillate  is  often  collected.  The  residue  in  the  pot  is  then  soluble" 
in  the  hot  boiled  oil,  which  is  run  direct  from  the  boiling  kettle  into 
the  resin  melting  kettle.  After  thorough  stirring  the  mixture  is 
usually  heated  some  time  longer  to  secure  homogeneous  solution.  It 
is  then  cooled  to  about  130°  or  140°  C.,  and  thinned  to  the  desired 
consistency  with  oil  of  turpentine.  The  varnish  is  allowed  to  stand 
in  storage  tanks  for  several  months,  or  even  for  a  year  or  two,  until 
thoroughly  clarified. 

The  boiling  of  the  oil  and  of  the  varnish  involves  considerable  risk 
from  fire.  The  oil  froths  very  much,  and  the  vapors  given  off  are 
inflammable,  hence  it  is  usually  the  custom  to  build  the  furnace  with 
the  fire-door  opening  through  a  partition  into  another  room.  The 
vapors  should  be  led  into  a  flue  having  a  good  draught. 

OLEO-RESINS 

Oleo-resins  are  mixtures  of  the  resin  and  the  essential  oil  of  the 
plant  from  which  they  exude.  Among  them  is  a  group  of  substances 
which  have  peculiar  odor  and  pungent  taste,  and  which  are  called 
balsams.  They  are  the  exudations  from  tropical  trees  belonging  to 
the  genera  Myroxylon  and  Styrax.  The  most  important  are  Benzoin, 
Peru,  Tolu,  and  Storax  balsams.  They  contain  free  benzoic  or  cin- 
namic  acids,  or  compounds  of  them,  to  which  their  peculiar  properties 
are  due.  The  balsams  are  chiefly  used  in  medicine  and  pharmacy, 
and  for  incense  and  perfumes. 

The  so-called  Canada  balsam  is  an  oleo-resin  containing  turpen- 
tine, and  is  not  a  true  balsam. 

GUM  RESINS 

Gum  resins  are  exudations  from  plants ;  they  are  the  inspissated 
juice,  and  contain  both  gum  and  resin.  They  form  emulsions  with 
water,  a  portion  of  the  gum  dissolving. 

Ammoniacum  is  derived  from  a  Persian  plant,  Dorema  Ammonia- 
cum,  Don.  It  forms  drops,  yellow  on  the  surface  and  milky  within. 
It  is  partly  soluble  in  water,  and  has  a  peculiar  odor  and  bitter  taste. 
It  is  employed  in  medicine. 

Asafoetida  is  obtained  from  the  roots  of  two  plants,  Ferula  Nar- 
thex,  Boiss.,  and  F.  fatida,  Regel,  native  in  Thibet  and  Turkistan. 
It  forms  tears'  and  nodules,  frequently  contaminated  with  earthy 
impurities.  It  has  a  powerful  garlic  odor  and  bitter  taste.  It  is 
mainly  used  in  medicine  as  a  stimulant. 


RESINS  AND   GUMS  399 

Euphorbium  is  derived  from  a  species  of  cactus,  Euphorbia  resini- 
fera,  Berg.,  native  in  Morocco.  It  has  a  very  pungent  taste,  an  aro- 
matic odor,  and  the  powdered  gum  irritates  the  throat  and  nose. 
It  is  a  violent  emetic  and  purgative,  and  is  chiefly  used  in  veteri- 
nary medicine. 

Galbanum  is  obtained  from  Persian  plants,  probably  Ferula  gal- 
baniflua,  Boiss.  &  Buhse.  It  forms  tears,  or  irregular  lumps,  of 
brownish  yellow  color,  aromatic  odor,  and  bitter  taste.  The  several 
varieties  found  in  commerce  are  used  in  medicine,  and  as  constit- 
uents of  incense. 

Gamboge  (p.  241)  is  an  orange-red  substance,  derived  from  a  tree, 
Garcinia  Hanburyi,  Hook.,  or  G.  Morella,  Desr.,  native  in  Cochin 
China  and  Siam.  It  is  soluble  in  alcohol,  has  an  acrid  taste,  and  is 
a  powerful  purgative.  Its  chief  uses  are  in  medicine,  and  as  a 
pigment. 

Myrrh  is  obtained  from  a  shrub,  Commiphora  Myrrha,  Engl., 
growing  on  the  coast  of  Arabia.  It  comes  in  commerce  as  red- 
brown,  dusty  lumps,  breaking  with  an  oily-appearing  fracture.  It 
has  a  fragrant  odor  and  bitter  taste,  and  emulsifies  with  water. 
It  is  used  as  a  tonic  in  medicine,  and  in  preparing  incense. 

Olibanum  or  frankincense  is  derived  from  several  species  of  Bos- 
wellia,  the  trees  being  native  in  Africa  and  Arabia.  It  forms  tears 
of  a  yellow-brown  color  and  milky  appearance.  It  has  a  slight 
turpentine-like  taste,  and  an  aromatic  odor.  It  forms  an  emulsion 
with  water,  and  was  formerly  much  used  in  medicine.  It  is  now 
chiefly  employed  in  preparing  incense. 

GUMS 

Gums  are  amorphous  bodies  of  complex  constitution,  nearly  all  of 
vegetable  origin,  and  soluble  in,  or,  at  least,  gelatinizing  with  water, 
but  insoluble  in  alcohol.  When  boiled  with  dilute  acid,  they  yield 
sugars,  and  when  oxidized  are  converted  into  oxalic  or  mucic  acids. 

Acacia,  Gum  Arabic,  or  Gum  Senegal,  is  derived  from  numer- 
ous plants  of  the  Acacia  family,  mostly  native  in  Africa.  It  forms 
lumps  of  various  sizes,  ranging  in  color  from  transparent  white  to 
red-brown.  Its  chief  constituent  is  arabic  acid,  or  arabin,  C^H^On, 
as  calcium  salt.  It  dissolves  in  cold  or  hot  water  with  equal  readi- 
ness, and  is  much  used  in  pharmacy  in  preparing  emulsions.  Low 
grades  are  used  for  mucilage,  in  calico  printing,  in  thickening  ink 
and  water  colors,  and  as  stiffening  in  cloth. 


400  OUTLINES  OF   INDUSTRIAL  CHEMISTRY 

Tragacanth  is  an  exudation  from  Astragalus  gummifer,  Labill., 
growing  in  the  Levant.  It  forms  dull  white,  translucent  plates, 
which  swell  in  water  and  partly  dissolve,  forming  a  thick  mucilage. 
Its  uses  are  similar  to  those  of  gum  arabic. 

Agar-agar  or  Bengal  isinglass  is  a  dried  seaweed,  Gracilaria  liche- 
noides  and  Eucheuma  spinosum,  collected  in  China.  It  forms  a  jelly 
with  water. 

Iceland  moss,  Cetraria  islandica,  yields  a  jelly  containing  two 
gums,  lichenine,  CeHioOs,  and  wolichenine.  The  former  is  not  colored 
blue  by  iodine,  while  the  latter  is. 

Irish  moss,  Chondrus  crispm,  yields  a  soluble  gum,  which  is  not 
colored  blue  by  iodine. 

REFERENCES 

Report  on  the  Gums,  Resins,  Oleo-resins,  and  Resinous  Products  of  India. 

M.  C.  Cooke,  London,  1874. 

Varnishes,  Lacquers,  Siccatives,  and  Sealing  Waxes.     E.  Andres.     Trans- 
lated by  Wm.  T.  Brannt,  Philadelphia,  1882.     (H.  C.  Baird  &  Son.) 
Oils  and  Varnishes.     James  Cameron,  Philadelphia,   1886.     (Blakiston, 

Son  &  Co.) 

Der  Fabrikation  der  Lacke  und  Firnisse.     Paul  Lohmann,  Berlin,  1890. 
Fossil  Resins.     C.  Lawn  and  H.  Booth,  New  York,  1891. 
Die  Fabrikation  der  Lacke  Firnisse,  u.  s.  w.  E.  Andres.      4te  Auf.     Wien, 

1891. 

Notes  on  Varnish  and  Fossil  Resins.     R.  I.  Clark,  London,  1892  (?). 
Painters'   Colours,   Oils,   and  Varnishes.     G.   H.   Hurst,   London,   1892. 
The  Chemistry  of  Paints  and  Painting.     A.  H.  Church.     2d  ed.     London, 

1892. 

Pigments,  Paints,  and  Painting.     G.  Terry,  London,  1893.     (Spon  &  Co.) 
Fabrication  des  Vernis.     L.  Naudin,  Paris,  1893. 
Die  Fabrikation  der  Copal-,   Turpentinol-  und  Spiritus-Lacke.     L.   E. 

Andes.     2te  Auf.     Wien,  1895.     (Hartleben.) 
Couleurs  et  Vernis.     G.  Halphen,  Paris,  1895. 

Die  Harze  und  ihre  Producte.     G.  Thenius,  Wien,  1895.     (Hartleben.) 
Gummi  arabicum  u.  dessen  Surrogate  in  festem  u.  niissigem  Zustande. 

L.  E,  Andes,  Wien,  1896.     (Hartleben.) 

Die  Aetherischen  Oele.     Gildemeister  und  Hoffmann,  Berlin,  1899. 
The  Chemistry  of  Essential  Oils  and  Artificial  Perfumes.     E.  J.  Parry,  New 

York,  1900. 


STARCH,   DEXTRIN,  AND  GLUCOSE 

Starch  is  widely  and  abundantly  distributed  in  the  vegetable 
kingdom,  occurring  in  nearly  all  plants  in  a  greater  or  less  quantity. 
It  forms  rounded  grains  of  characteristic  appearance  in  the  several 
varieties,  and  is  most  abundant  in  the  fruit,  tubers,  seeds,  and  stems 
of  the  plants  from  which  it  is  industrially  obtained.  It  is  a  typical 
carbohydrate,  and  on  analysis  corresponds  to  the  formula  CeHioOs; 
but  it  is  probable  that  the  true  symbol  is  some  multiple  of  this,  and 
that  the  formula  should  be  written  (CeHioOs)^  where  n  is  4  or  more. 
Starch  has  not  yet  been  prepared  synthetically,  and  even  its  for- 
mation in  plants  is  not  fully  understood ;  but  it  appears  that  the 
chlorophyl  (the  green  coloring  matter  in  plants)  enters  into  the 
reaction  in  some  way,  perhaps  as  a  "  contact "  substance.  The 
carbon  dioxide  of  the  air  is  reduced  by  the  joint  action  of  the  chloro- 
phyl and  sunlight,  the  carbon  being  assimilated,  and  part  of  the 
oxygen,  at  least,  being  set  free.  The  formation  of  starch  might  be 
represented  thus :  — 

6  CO2  +  5  H2O  =  C6H10O5  +  6  O2. 

It  is,  however,  probably  not  formed  directly,  but  may  be  an  altera- 
tion product  of  the  sugar  which  is  so  formed.  As  hypothetical 
reactions,  the  following  will  serve  to  show  the  outline  of  the  process, 
but  it  is  by  no  means  certain  that  these  truly  represent  the  exact 
changes  which  occur :  — 

6  CO2  +  6  H2O  =  C6Hi2O6  +  6  O2. 
CeH^Oe  =  C6Hi0O5  +  H2O. 

It  appears  somewhat  improbable  that  substances  of  such  high  molec- 
ular weight  as  glucose,  C6Hi2O6,  or  starch,  should  be  formed  directly 
from  the  reduction  of  carbon  dioxide.  According  to  Baeyer,*  it  is 
more  probable  that  formaldehyde,  CH2O,  is  first  produced,  and 
then  by  a  polymerization  process,  the  glucose  is  formed,  from  which 
starch  is  derived :  — 

6  CO2  -f  6  H2O  =  6  CH2O  +  6  O2. 
6  CH2O  =  C6Hi2O6. 

The  starch  is  formed  in  the  leaves  and  green  parts  of  the  plant, 
being  then  transported  in  soluble  form  to  the  other  parts,  where  it  is 

*  Berichte  der  deutschen  chemischen  Gesellschaft,  3,  67. 
2o  401 


402  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

at  once  applied  to  the  building  up  of  the  tissues,  or  is  deposited  as 
reserve  material  for  the  future  nourishment  of  the  plant,  or  of  a  new 
individual;  the  greatest  deposits  are  generally  found  in  the  roots, 
tubers,  or  seeds. 

As  seen  under  the  microscope,  a  starch  granule  is  made  up  of 
different  layers,  arranged  around  a  nucleus,  a  dark  interior  portion, 
generally  at  one  side  of  the  granule.  Each  granule  consists  of  an 
interior  substance  called  "  granulose,"  and  an  exterior  transparent 
covering,  inert  and  insoluble,  and  resembling  cellulose  in  structure. 
But  recent  investigations  tend  to  prove  that  the  "  starch  cellulose  " 
is  not  present  as  such  in  the  granule,  but  is  formed  from  the  starch 
substance  by  the  action  of  acids  or  by  fermentation. 

Starch  is  entirely  insoluble  in  cold-  water,  but  when  heated  to  70° 
or  80°  C.,  the  granules  swell  and  finally  burst,  and  the  starch  sub- 
stance, "granulose,"  combines  with  the  water  to  form  paste.  When 
this  is  boiled  in  an  excess  of  water,  it  goes  into  solution  and  may  be 
filtered.  The  solution  yields  an  intense  blue  color  with  iodine,  hence 
its  use  as  an  "  indicator  "  ;  it  is  optically  active  and  rotates  the  plane 
of  polarization  tr  the  left. 

By  exposing  starch  to  the  action  of  cold  dilute  mineral  acid  for 
several  days,  it  is  converted  into  a  soluble  modification  called  amylo- 
dextrin,  which  dissolves  in  warm  water  without  forming  a  paste. 
When  heated  dry  to  200°  C.,  starch  is  converted  into  dextrine  or 
British  gum. 

The  chief  industrial  sources  of  starch  are  potatoes,  wheat,  corn, 
rice,  arrowroot,  and  certain  varieties  of  palm  trees  (sago).  In  Europe, 
potatoes,  rice,  and  wheat  are  used,  while  in  this  country  corn  and 
wheat  are  mainly  employed.  The  separation  of  the  starch,  which  is 
mixed  with  various  nitrogenous  and  fatty  matters  and  some  mineral 
impurities,  is  essentially  a  mechanical  process ;  but  much  care  is 
needed  to  prevent  changes  which  would  spoil  the  product. 

Corn  starch  *  is  usually  made  by  the  alkaline  or  "  sweet  "  process  ; 
sometimes  by  an  acid  or  fermentation  method  similar  to  that  em- 
ployed for  wheat  starch.  In  the  alkaline  process  the  grain  is  run 
through  a  fanning  mill  to  blow  away  dust,  husks,  etc.,  and  is  then 
steeped  in  water  at  from  70°  to  140°  F.  for  from  three  to  ten  days, 
when  the  softened  grains  are  crushed  between  rolls.  This  steeping 
removes  much  of  the  oil  and  swells  the  gluten  and  albuminous  matter 
so  that  it  is  readily  attacked  by  the  alkali.  After  a  time  putrefactive 
fermentation  sets  in  and  hydrogen  sulphide  is  evolved.  Since  this 
*  J.  Soc.  Chem.  Ind.,  1887,  80.  1902,  4.  Geo.  Archbold. 


STARCH,    DEXTRIN,   AND   GLUCOSE  403 

causes  a  nuisance,  tfie  method  has  been  replaced  in  some  factories 
by  the  Durgen  system,  in  which  a  continuous  stream  of  water  at 
130°  to  140°  F.  flows  slowly  through  the  steeping  tanks.  After 
three  days  the  grain  is  soft,  while  a  large  quantity  of  extractive 
matter  has  been  washed  away.  The  grain  is  then  ground  in  buhr- 
stone  and  roller  mills  through  which  water  is  flowing;  the  starchy 
magma  goes  to  revolving  sieves  of  brass  wire  for  the  coarser  strain- 
ing, and  then  to  cylindrical  reels  covered  with  bolting  cloth.  The 
mass  which  passes  over  the  sieves  is  reground  and  again  sifted. 
The  waste  glutinous  matter  is  pressed  and  dried  for  cattle  feeding, 
or  is  sold  wet  as  "  swill  "  for  hogs. 

The  milky  liquor  from  the  sieves  is  settled  and  drawn  off  from 
the  crude  starch,  which  is  washed  twice  with  fresh  water  and  then 
pumped  into  vats  having  good  stirring  apparatus,  and  provided  with 
holes  in  the  sides,  closed  by  plugs  and  used  for  decanting  the  liquor. 
A  dilute  caustic  soda  solution  of  7°  or  8°  Be.  is  stirred  into  the  starch 
until  the  liquid  becomes  greenish  yellow ;  then  the  whole  is  stirred 
for  several  hours.  When  a  test  shows  that  the  suspended  matter 
settles  in  two  layers,  the  starch  on  top,  sedimentation  is  allowed  to 
take  place  and  the  supernatant  liquor,  containing  much  oil  and 
nitrogenous  matter  in  solution,  is  drawn  off.  The  sediment  is  stirred 
up  with  water,  allowed  to  stand  until  the  gluten  has  deposited, 
and  then,  by  pulling  the  plugs  in  succession,  the  starch  in  suspen- 
sion is  "  siphoned  off  "  into  tanks.  By  several  repetitions  of  this 
process  the  starch  is  nearly  all  removed  from  the  gluten  and  at  the 
same  time  is  separated  into  several  grades.  The  residue  then  flows 
on  to  a  long,  slightly  inclined  table,  or  "  run,"  from  60  to  120  feet 
long  and  having  a  fall  of  3  or  4  inches.  A  stream  of  water  flows 
slowly  over  it  and  washes  away  the  gluten  and  fibrous  matter,  while 
the  starch  deposits  on  the  table. 

The  starch  collected  in  the  several  tanks  is  washed  with  water 
and  sometimes  again  siphoned,  and  is  then  run  through  bolting 
cloth  to  the  settling  tanks,  where  it  deposits  in  a  dense  compact 
layer  from  which  the  water  can  be  drawn  off.  The  wet  starch  is  then 
shovelled  into  frames  lined  with  cloth  .and  having  perforated  bottoms, 
through  which  the  water  drains.  The  cake  of  damp  starch  is  cut 
into  smaller  blocks  and  placed  on  porous  floors  of  plaster  of  Paris 
or  brick,  which  absorb  the  adhering  water.*  The  starch  is  removed 
to  the  dry  room  and  kept  at  a  temperature  of  125°  F.  for  several 

*  These  floors  may  be  subsequently  dried  by  passing  hot  air  through  flues  ar- 
ranged in  them. 


404  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

days.  While  it  is  drying,  the  impurities  still  remaining  in  it  find 
their  way  to  the  surface,  where  they  form  a  yellowish  deposit  which 
is  cut  away  when  the  starch  is  nearly  dry.  The  block  is  then  wrapped 
in  paper  and  further  dried  at  150°  to  170°  F.  for  several  days.  Dur- 
ing this  time  the  mass  contracts  and  cracks  into  a  number  of  irreg- 
ularly shaped  prismatic  rods,  called  "  crystals,"  though  they  are  not 
true  crystals.  The  entire  drying  process  requires  several  weeks,  and 
the  product  as  sent  to  market  contains  about  10  to  12  per  cent  of  water. 

An  improved  process  is  now  used  as  follows :  The  shelled  corn  is 
screened  to  remove  dirt,  husks,  etc. ;  it  then  passes  magnets  to  re- 
move nails  or  bits  of  iron,  and  then  goes  into  wooden  "  steep-tanks  " 
of  1000  to  1500  bushels  capacity.  Each  tank  has  a  false  bottom,  and 
a  circulation  pipe  on  the  outside,  passing  from  the  false  bottom  to  near 
the  top  of  the  tank.  Steam  can  be  injected  into  the  pipe  to  maintain 
the  circulation  and  keep  the  steep  water  at  about  60°  C.  Steeping 
continues  24  hours  or  more,  and  the  steep  liquor  contains  about  0.3 
per  cent  sulphurous  acid  to  prevent  fermentation.  The  liquor  is  drawn 
off  and  the  softened  grain  crushed  in  "  cracker  "  mills  to  loosen  the 
germs.  These  mills  are  large  disks,  set  face  to  face,  having  projecting 
teeth  and  rotating  in  opposite  directions. 

The  coarse  meal  passes  to  "  separators,"  long,  narrow  tanks,  con- 
taining a  starch  milk  of  10°  to  12°  Be.,  calcium  chloride  being  some- 
times dissolved  in  the  liquor  to  increase  its  density.  The  germs,  being 
light,  float  over  the  dam  at  the  end  of  the  tank,  while  the  hulls  and 
starchy  portions  sink,  and  pass  out  by  an  opening  at  the  bottom  of 
the  tank.  The  germs  pass  over  copper  screens  or  "  shakers,"  where 
they  are  sprinkled  with  water  to  free  them  from  adhering  starch ;  the 
starch  milk  thus  obtained  is  returned  to  the  separator. 

The  germs  are  pressed  to  remove  water,  dried,  and  ground  fine; 
the  meal  is  heated  and  heavily  pressed  in  a  hydraulic  press  (p.  353) 
to  obtain  the  corn  oil ;  the  oil  cake  is  sold  for  cattle  food. 

The  hulls  and  starchy  matter  from  the  separators  are  ground  fine 
in  buhrstone  mills  and  passed  over  copper  "shakers,"  some  of  the  starch 
milk  going  back  to  the  separators,  and  the  rest  passing  to  shakers 
covered  with  silk  bolting  cloth ;  the  chaff  and  husks  are  reground  and 
passed  through  a  slop  machine  to  remove  the  last  portion  of  starch. 

The  starch  liquors,  containing  gluten  and  other  substances,  are 
agitated  in  a  mixing  tank  with  dilute  caustic  soda  solution ;  this  dis- 
solves some  of  the  gluten,  swells  the  remainder,  neutralizes  the  acid, 
and  coagulates  the  fine  suspended  impurities.  The  magma  then 
goes  to  the  "  runs,"  or  "  table,"  where  the  starch  deposits,  the  lighter 


STARCH,    DEXTRIN,   AND   GLUCOSE  405 

gluten  being  washec|  into  a  settling  tank,  from  which  it  is  pumped 
into  a  filter-press  to  remove  the  water.  The  gluten  is  then  dried 
and  sold  as  sucli,  or  is  pulverized  and  mixed  with  the  bran  and  husks 
from  the  slop  machine.  The  steep  water  from  the  softening  of  the 
grain  carries  considerable  soluble  matter  and  is  evaporated  to  about 
30°  Be.,  and  mixed  with  the  bran  and  husks  before  drying. 

The  "  green  starch  "  from  the  tables  is  usually  mixed  with  water 
and  again  passed  over  the  tables,  when  dry  starch  is  to  be  made. 

Centrifugal  machines  are  sometimes  used  for  separating  the 
starch  from  the  wash  water.  These  machines  are  of  two  kinds, 
those  having  a  perforated  basket,  and  those  in  which  the  basket 
is  of  unperf orated  sheet  metal.  In  the  latter,  the  starch  is  thrown 
against  the  cylinder  wall  and  packed  so  firmly  that  it  remains  as 
a  thick  layer,  while  the  water  collects  in  the  middle  of  the  drum 
and  can  be  drawn  off  very  completely,  carrying  with  it  much  of  the 
glutinous  and  fibrous  matter.  In  a  perforated  drum  the  water 
passes  through,  leaving  the  solid  matter  behind.  The  starch,  being 
heavier  than  the  cellulose,  forms  a  layer  directly  on  the  basket  walls, 
while  inside  of  this  is  a  layer  of  gray  starch  containing  the  impuri- 
ties ;  this  latter  is  scraped  off  and  washed  again.  The  starchy 
liquid  running  into  the  basket  must  not  be  too  thick,  otherwise  the 
load  does  not  distribute  itself  evenly  in  the  basket. 

Corn  contains  about  54  per  cent  of  starch,  and  the  actual  yield 
obtained  in  technical  work  is  about  50  per  cent,  or  28  pounds  of 
starch  from  a  bushel  (56  pounds)  of  corn.  About  13  pounds  of  glu- 
ten suitable  for  cattle  food  is  also  recovered  per  bushel  of  corn. 

The  best  grade  of  corn  starch  is  largely  consumed  for  food,  but  its 
principal  use  is  in  laundry  work.  Lower  grades  are  chiefly  employed 
in  manufacturing  and  in  textile  industries.  In  some  technical  opera- 
tions the  so-called  "  green  starch  "  is  used.  This  is  the  product 
obtained  directly  from  the  inclined  table,  settling  tanks,  or  centrifu- 
gal machine  after  a  partial  drying.  It  contains  some  impurities 
and  is  generally  damp,  often  containing  40  per  cent  of  water.  It  is 
mainly  employed  for  glucose  making,  for  stiffening  and  size,  in  color 
mixing  for  calico  printing,  and  in  the  manufacture  of  paper  boxes. 

The  old  fermentation  processes  of  starch  extraction  destroy  the 
gluten  and  cause  incipient  hydrolysis  of  the  product ;  the  paste  made 
from  such  starch  is  more  limpid  than  that  of  starch  made  by  newer 
methods  in  which  these  changes  do  not  occur.  In  modern  work, 
to  obtain  this  quality  of  "  thin  boiling  "  paste,  the  starch,  after 
separation  from  the  gluten,  is  given  a  mild  treatment  with  mineral 


406 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


acid  at  temperatures  of  26°  to  40°  C.  Thin  boiling  starch  is  preferred 
for  textile  work  because  oi  the  greater  fluidity  and  better  penetra- 
tion of  the  paste  into  the  fabric. 

OUTLINE    OF   THE   PROCESS  FOR   CORN   STARCH 

Corn 

I 
(A)  Steeped 

(£)  Crushed 

I 
(C)   Germ  separators 


Germ 

i 

Ground 

I 
Pressed 

i 


I 

Corn  meal 

I 

Ground  fine  (buhrstones) 

I 

Passed  twice  over  shakers  which 
are  sprinkled  with  water 


Oil  cake 


Corn  oil 


(E)  Starch  water 

I 
Carries  starch  and  gluten 


Agitated  in  tank 

Fed  to  "runs"  or  tables 
(120  ft.  by  2  ft.,  with 
gentle  incline) 


I 
(D)  Husks 

I 
Reground  (steel  rolls) 

I 

"Slop"  passed  through 
slop  machine,  a  wringer 
to  remove  residual  starch 
water 


Starch  water       Wet  feed 


Gluten 

I 
Settled 


returned 
Starch      to  (E) 


Liquor 

I 
Rejected 


Gluten 

I 
Filter-pressed 

Cake  ground  and  passed 
through  driers 


Consists  of 

husk  and  bits 

of  germ 

I 
Passed  to  dry 

room 

I 

Dry  feed 


Process  generally  repeated 

i 
Cooled 

I 
Bagged 


STARCH,    DEXTRIN,   AND   GLUCOSE  407 

Wheat  starch  is  made  by  the  fermentation  or  "sour  "  process,  or 
by  Martin's  process  without  fermentation. 

By  the  sour  process,  all  the  gluten,  of  which  wheat  contains  a 
large  amount,  is  destroyed,  consequently  there  is  considerable  loss. 
The  grain  is  soaked  in  water  until  soft,  and  then  crushed  between 
rolls  or  pressed  in  bags.  The  starch  is  washed  out  of  the  crushed 
pulp  with  water,  and  the  milky  liquid  is  run  into  tanks  and  allowed 
to  ferment.  In  order  to  hasten  this,  some  of  the  sour  liquor  from  a 
previous  fermentation  is  added.  The  temperature  is  kept  at  about 
20°  C.,  and  the  contents  of  the  cistern  well  stirred  frequently.  The 
fermentation  lasts  from  10  to  14  days;  the  sugar,  albumin,  and 
gummy  matters  of  the  wheat  undergo  an  alcoholic  fermentation, 
followed  by  the  development  of  acetic,  lactic,  and  butyric  acids. 
These  acids  then  attack  the  gluten,  dissolving  it  in  part,  and  de- 
stroy its  tough  and  sticky  properties,  so  that  it  is  easily  washed 
free  from  the  starch.  The  washing  is  done  in  revolving  sieves,  in 
which  the  swollen  gluten,  cellulose,  etc.,  remain.  The  starch  is  re- 
peatedly washed  and  sieved,  or  levigated,  until  sufficiently  pure  and 
white,  when  it  is  dried  as  already  described  under  corn  starch;  but 
more  care  is  necessary,  because  of  the  tendency  of  the  mass  to  cake 
together,  owing  to  the  presence  of  a  trace  of  gluten.  The  process 
must  be  carefully  watched  lest  the  fermentation  go  too  far  and  putre- 
faction set  in,  thus  causing  a  loss  of  starch.  The  acid  waste  liquors 
are  difficult  to  dispose  of,  and  cause  considerable  nuisance  in  the 
neighborhood.  Usually  about  59  pounds  of  starch  and  11  pounds 
of  bran  are  obtained  from  100  pounds  of  wheat.  But  only  a  small 
quantity  of  sour  gluten  is  recovered. 

By  Martin's  process  part  of  the  nitrogenous  matter  (gluten)  is 
recovered.  Ordinary  wheat  flour  from  which  the  bran  has  been 
removed  is  used  instead  of  the  whole  grain.  The  flour  is  kneaded 
with  40  per  cent  of  water  to  form  a  stiff  dough,  which  is  then  washed 
in  small  portions  at  a  time  in  a  fine  sieve,  while  small  jets  of  water 
continually  play  upon  the  mass,  carrying  away  the  starch.  By 
treating  the  partly  washed  starch  with  a  solution  of  caustic  soda 
(sp.  gr.  1.013)  and  allowing  it  to  stand  a  few  hours,  the  remaining 
gluten  is  swollen  and  may  be  removed  by  sieving  on  bolting  cloth. 
The  pasty  mass  of  gluten  left  in  the  sieves  is  utilized  in  the  manu- 
facture of  macaroni,  noodles,  and  gluten  bread,  but  more  especially 
for  paste  and  for  cement  for  leather,  and  as  a  thickening  material 
instead  of  casein  or  albumin  in  textile  working. 

Fesca's  modification  of  Martin's  process  consists  in  stirring  wheat 


408  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

flour  into  water  to  form  a  thin  "  milk,"  which  is  then  run  into  cen- 
trifugal machines.  The  starch,  being  heavier  than  the  gluten,  col- 
lects next  the  revolving  sieve.  The  interior  layer,  consisting  of  a 
mixture  of  starch  and  gluten,  is  removed,  washed  with  water,  and 
again  "  centriffed."  But  much  starch  remains  in  the  gluten. 

The  yield  by  Martin's  method  is  about  55  pounds  of  starch  and 
12  pounds  of  gluten  from  100  pounds  of  wheat.  By  Fesca's  process, 
only  40  to  45  pounds  of  starch  are  obtained  from  100  pounds  of  wheat. 

Potato  starch  is  most  important  in  Europe.  The  tubers  contain 
an  average  of  about  20  per  cent  of  starch  and  75  per  cent  water. 
The  skin  contains  some  fats  and  coloring  matter,  but  no  starch. 
The  adhering  dirt  and  sand  are  carefully  removed  by  washing  in 
a  revolving  drum  made  of  wood  or  iron  slats  with  narrow  openings 
between  them  for  the  escape  of  the  dirt,  etc.  Inside  the  drum  are 
revolving  arms  which  rub  the  potatoes  together,  or  revolving  wire 
or  bristle  brushes  which  scrub  them  as  the  drum  turns.  The  wash- 
ing must  be  thorough  or  the  quality  of  the  starch  suffers.  The  tubers 
are  next  rasped  or  ground  in  a  machine  consisting  of  a  revolving 
cylinder  or  roll,  around  whose  outer  surface  are  set  a  large  number 
of  narrow  knife-edges  or  saw-blades,  which  project  about  one-fifth 
of  an  inch.  These  knife-edges  rotate  very  close  to  fixed  wooden  bars 
which  catch  and  hold  the  potato  while  it  is  scraped  into  soft  pulp. 

The  starch  in  the  potato  is  enclosed  in  little  cells  or  bags  of  cellu- 
lose, a  number  of  granules  being  in  each  cell.  Since  the  starch  can 
only  be  washed  away  from  the  ruptured  cells,  the  finer  the  pulp  the 
larger  the  yield  of  starch.  But  even  with  the  best  raspers  many 
cells  escape  unbroken,  and  usually  about  15  per  cent  of  the  starch  is 
lost.  Sometimes  the  pulp  is  reground  after  it  has  been  washed, 
which  increases  the  yield  of  starch  slightly. 

The  pulp,  consisting  of  starch  and  cellulose  fibre  and  tissue, 
passes  into  a  series  of  shaking  sieves,  where  the  starch  is  washed 
away  with  a  limited  amount  of  water.  A  better  apparatus  consists 
of  a  series  of  revolving  wire  gauze  cylinders  (30  to  35  meshes  to  the 
inch),  containing  brushes  which  revolve  in  a  direction  opposite  to 
the  motion  of  the  cylinder.  Fine  jets  of  water  play  upon  the  pulp 
and  wash  out  the  starch.  The  milky  liquor  passes  to  a  revolving 
sieve  with  50  meshes  per  inch,  which  retains  any  fibre  that  passes 
through  the  coarser  screens.  Long  semicylindrical  sieves  contain- 
ing brushes  set  in  the  form  of  an  Archimedian  screw  around  a  revolving 
shaft  are  sometimes  used.  The  brushes  push  the  pulp  along  from  one 


STARCH,   DEXTRIN,   AND   GLUCOSE  409 

end  to  the  other,  at  -the  same  time  thoroughly  working  it  over,  while 
the  starch  is  washed  out  by  jets  of  water.  The  waste  pulp  passing 
over  the  sieves  is  treated  by  Biittner  and  Meyer's  process;  it  is 
pressed  and  dried  rapidly  until  the  moisture  is  about  12  per  cent. 
It  is  sold  as  a  low-grade  cattle  food. 

The  starch  suspended  in  the  wash  water  is  run  over  inclined  tables 
similar  to  those  already  described.  The  crude  product  is  stirred  up 
with  water  in  a  tank,  and  after  the  sand  and  heavy  dirt  have  settled, 
the  starch  in  suspension  is  rapidly  "  siphoned  "  off  through  holes  in 
the  side  of  the  tank.  By  levigation,  the  starch  is  obtained  in  several 
grades  of  purity.  Centrifugal  machines  are  also  employed  to  separate 
the  starch  and  wash  water,  but  with  less  success  than  in  the  case  of 
corn,  wheat,  or  rice  starch. 

The  crude  starch  obtained  by  any  of  'these  methods  is  purified 
by  repeated  washings  and  levigation,  with  an  occasional  passing 
through  sieves  or  bolting  cloth  to  remove  fibre.  The  purified  starch 
is  dried  in  much  the  same  way  as  is  corn  starch. 

Potato  starch  is  also  made  by  the  "  rotting  "  process,  in  which 
the  moist,  sliced  material  is  heaped  in  a  warm  room.  Fermentation 
and  ultimate  decomposition  of  the  cell  walls  takes  place,  so  that  the 
starch  can  be  washed  out  of  the  pulp.  Much  care  is  necessary  that 
the  fermentation  does  not  attack  the  starch  itself.  The  mass  must 
be  turned  over  frequently  during  decomposition. 

The  wash  waters  from  potato  starch  contain  much  potash,  phos- 
phoric acid,  albumin,  and  nitrogenous  matter,  which  soon  ferment 
and  become  very  offensive.  If  possible,  they  should  be  used  at  once 
to  irrigate  land.  Much  ingenuity  has  been  expended  to  devise  means 
of  making  them  less  offensive,  but  without  much  success. 

The  yield  from  100  pounds  of  potatoes  is  about  15  or  16  pounds 
of  dry  starch.  The  product  is  chiefly  used  in  the  textile  industries, 
for  laundry  purposes,  and  in  glucose  and  dextrine  making ;  for  the 
two  last  mentioned  it  is  customary  to  use  the  "  green  starch,"  con- 
taining from  30  to  40  per  cent  water. 

Rice  starch  *  is  chiefly  produced  in  Europe,  only  the  broken 
grains  separated  with  the  husks  in  the  cleansing  mills  being  used. 
Rice  contains  nearly  80  per  cent  of  starch,  but  its  separation  is  diffi- 
cult, since  the  cells  of  the  grain  are  composed  of  dense  glutinous 
material  and  the  starch  granules  are  cemented  together  solidly  by 
albuminous  and  gummy  matter.  In  order  to  soften  the  gluten,  the 
rice  is  macerated  in  dilute  caustic  soda  (sp.  gr.  1.007)  containing 
*  J.  Berger,  Chem.  Zeitung,  14,  1440  and  1571 ;  15,  843. 


410  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

about  0.5  per  cent  caustic.  After  soaking  about  18  hours  with  fre- 
quent stirring,  the  liquor  is  drawn  off  and  a  fresh  caustic  solu- 
tion is  added.  When  the  grain  is  soft,  it  is  crushed  in  mills  while 
a  stream  of  dilute  caustic  plays  over  the  mass,  dissolving  a  part  of 
the  glutinous  matter,  and  swelling  the  remainder  so  that  it,  together 
with  the  fibrous  matter,  may  be  removed  by  sieving.  The  starch 
is  then  separated  from  the  liquor  by  centrifugal  machines,  and  further 
purified  by  washing  it  with  water,  running  it  through  centrifugal  ma- 
chines or  settling  tanks,  and  finally  filter-pressing  and  drying  in  much 
the  same  way  as  for  corn  starch.  The  yield  is  about  85  per  cent  of 
the  total  starch  in  the  rice.  The  fibrous  matter  and  gluten  passing 
over  the  sieves  are  used  as  cattle  food,  or  if  carefully  dried  and  pul- 
verized, are  sometimes  sold  as  "  rice  meal."  The  caustic  solutions 
contain  gluten  which  is  precipitated  by  acidifying  them.  Much  care 
is  necessary  to  prevent  any  fermentation  of  the  liquors  or  of  the  wet 
starch,  if  the  drying  be  too  slow.  In  order  to  correct  the  slight  yellow 
tinge,  due  to  traces  of  impurity  in  the  starch,  a  little  ultramarine  is 
generally  added  in  the  settling  tanks  or  centrifugals.  Prussian  blue  or 
alkali  blues  which  are  not  fast  against  alkali  should  not  be  used. 

Sago  is  a  starch  prepared  from  the  pith  of  several  varieties  of 
palm  trees  (genera  Metroxylon,  Arenga,  and  Borassm),  indigenous  in 
the  East  Indies.  The  trees  are  cut  down  and  the  pith,  sometimes 
amounting  to  700  pounds  from  one  tree,  is  removed  from  the  trunks. 
It  is  a  mixture  of  starch  and  woody  fibre  and  is  pounded  fine  in  wooden 
mortars ;  the  starch  is  washed  out  with  water  and  purified  by  sieving 
and  washing  as  in  other  cases.  This  furnishes  the  sago  flour  of  com- 
merce. Pearl  sago  is  made  by  kneading  the  sago  flour  to  a  dough  with 
water,  and  then  working  the  dough  through  a  sieve  into  a  hot  pan, 
greased  with  oil,  and  kept  shaking  constantly ;  a  portion  of  the  starch 
is  converted  into  paste  by  the  heat,  and  coats  the  outside  of  the 
granules,  which  then  stick  together  and  form  little  translucent  globules. 
Imitation  sago  is  now  made  from  potato  or  other  starch.  Sago  is 
chiefly  used  as  food  and  swells  in  hot  water  without  destroying  the 
globular  form. 

Arrowroot  *  starch  is  obtained  from  the  roots  of  several  varieties 
of  plants  belonging  to  the  genus  Maranta.  The  long,  slender  roots 
are  soaked  in  water  until  the  coarse  outer  skin  softens,  when  it  is 
stripped  off.  After  washing,  the  roots  are  rasped  to  a  pulp,  from 
which  the  starch  is  washed  with  water,  sieved,  and  settled  to  remove 
fibrous  matter  and  soluble  impurities.  Owing  to  the  large  amount 
*  J.  Soc.  Chem.  Ind.,  1887,  334. 


STARCH,    DEXTRIN,   AND   GLUCOSE  411 

of  fibre  present,  fine  grinding  is  difficult,  and  considerable  starch  is 
lost  in  the  waste  pulp.  Also,  there  is  much  trouble  in  sieving ;  hand 
sieves  are  used,  since  mechanical  ones  soon  become  choked  by  the 
fibres.  The  starch  is  dried  in  the  open  air  on  wire  screens  until  no 
more  than  14  to  17  per  cent  of  water  remains.  The  drying  house 
is  a  light  shed,  open  on  all  sides  for  the  free  circulation  of  air.  In 
damp  weather  much  care  is  necessary  to  keep  the  wet  starch  from 
souring,  especially  if  any  impurity  is  present.  Arrowroot  starch  is 
much  used  for  food,  but  is  also  desirable  for  laundry  and  sizing  pur- 
poses. It  forms  a  stiffer  jelly  than  do  most  other  starches. 

Cassava  starch  is  similar  to  arrowroot  and  is  obtained  from  the 
roots  of  several  species  of  Manihot,  which  are  indigenous  in  Brazil, 
but  which  are  now  cultivated  in  other  tropical  countries.  The 
starch  is  also  called  Brazilian  arrowroot  and  is  prepared  similarly 
to  the  true  arrowroot.  By  heating  the  damp  starch  in  shallow  pans 
while  stirring  actively,  the  granules  burst  and  adhere  together,  form- 
ing the  mass  into  small,  irregularly  shaped  translucent  kernels,  known 
as  tapioca.  This  is  somewhat  soluble  in  cold  water,  and  is  very 
easily  swelled  by  boiling  water  to  form  a  transparent  jelly. 

There  are  several  other  starches  similar  to  sago  and  cassava  which 
are  used  as  food,  the  most  important  of  these  being  curcuma,  tous- 
les-mois,  and  arum.  Some  starch  is  prepared  from  the  nuts  of  the 
horse-chestnut  tree,  JEsculus  Hippocastanum,  L.,  which  contains  about 
25  per  cent  of  starch.  But  since  it  is  nearly  impossible  to  remove 
the  bitter  principles,  the  starch  is  only  used  for  stiffening  and  sizing 
purposes. 

The  chief  uses  of  starch  are :  for  stiffening  purposes  in  laundry 
work  and  finishing  cotton  cloth  —  rice  starch  is  best  for  this  and  the 
addition  of  a  little  paraffine  or  stearin  increases  the  gloss ;  for  thick- 
ening material  in  calico  printing ;  as  paste  for  adhesive  purposes  — 
for  which  wheat  starch  is  best ;  in  sizing  paper ;  for  glucose  making, 
in  which  corn  or  potato  starch  is  generally  used ;  as  a  food ;  and  as  a 
toilet  powder,  for  which  rice  starch  is  generally  preferred. 

Starch  is  readily  detected  by  the  microscope  or  by  use  of  a  solu- 
tion of  iodine.  There  are  several  methods  for  determining  the 
amount  of  starch  in  a  given  substance,  but  nearly  all  of  them  de- 
pend upon  the  direct  isolation  of  the  starch,  or  its  conversion  into 
sugar,  which  is  then  determined  by  means  of  Fehling's  solution. 


412  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

DEXTRIN 

Dextrin  corresponds  to  the  formula  (Ci2H2oOio)w  •  H2O  and  is  some- 
times considered  an  intermediate  product  between  starch  and  dex- 
trose. The  commercial  product,  called  dextrine,  or  British  gum,  is 
made  by  heating  dry  starch  to  a  temperature  of  200°  to  250°  C.  in  a 
revolving  iron  cylinder  over  free  flame,  or  in  an  oil  bath,  or  by  a  steam 
jacket;  or  the  starch  may  be  moistened  with  nitric  or  hydrochloric 
acid,  dried  at  50°  C.  and  then  heated  to  140°  to  170°  C. ;  this  gives 
a  lighter  colored  product,  but  since  it  contains  some  sugar,  its  ad- 
hesive power  is  less  than  if  made  without  acid.  After  roasting,  the 
dextrine  is  cooled  quickly  to  stop  the  conversion,  and  is  powdered 
in  a  mill  and  sieved  on  bolting  cloth.  The  product  is  an  indefinite 
mixture  of  several  dextrins  with  unchanged  starch.  The  dextrins 
are  soluble  in  cold  water  and  form  a  thick,  viscous  syrup  which  has 
strong  adhesive  properties  and  is  therefore  much  used  as  a  substitute 
for  gum  arabic  in  preparing  mucilage  and  for  thickening  colors  in  calico 
printing. 

By  acting  upon  starch  paste  with  diastase,  a  syrupy  liquid  con- 
taining dextrin  and  sugar  (maltose)  is  obtained;  starch  is  mixed 
with  water  at  50°  C.,  and  then  heated  to  65°  C.,  when  the  necessary 
amount  of  malt  (carrying  the  diastase)  is  added,  and  the  temperature 
raised  to  73°  C.,  until  iodine  gives  a  reddish  violet,  instead  of  a  blue 
color.  The  solution  is  then  boiled  to  destroy  any  remaining  diastase, 
cooled,  filtered,  and  concentrated  in  vacuo  to  the  desired  density. 
It  is  established  that  there  are  several  dextrins  produced  simul- 
taneously with  the  formation  of  the  sugar  by  this  action.  Dextrin 
syrups  are  used  in  brewing,  for  thickening  tanning  extracts,  and  in 
confectionery. 

The  products  obtained  by  these  various  methods  vary  somewhat 
in  their  properties,  and  have  been  assigned  distinguishing  names,  — 
erythrodextrin,  achrodextrin,  and  inaltodextrin.  They  are  all  soluble 
in  water,  insoluble  in  alcohol,  strongly  dextro-rotary,  and  yield  dex- 
trose by  hydrolysis.  Erythrodextrin  yields  a  red  color  with  iodine, 
while  the  others  yield  no  color. 

GLUCOSE 

Under  the  name  "  glucose  "  are  grouped  not  only  substances  de- 
rived from  starch  by  hydrolysis,  such  as  'dextrose,  maltose,  dextrins, 
etc.,  but  also  those  resulting  from  the  inversion  of  sugar,  such  as 
levulose. 


STARCH,    DEXTRIN,   AND    GLUCOSE  413 

Dextrose,  CeH^Oe,  and  the  isomeric  levulose  occur  in  the  juice 
of  many  fruits,  such  as  grapes,  cherries,  bananas,  pears,  etc.,  but  in 
quantities  varying  in  the  same  fruit,  according  to  the  season  and  the 
degree  of  ripeness.  But  these  sugars  are  seldom  made  from  fruit 
juice ;  dextrose  being  more  easily  obtained  from  starch.  Dextrose  is 
sometimes  sold  as  "  fruit  sugar,"  "  grape  sugar,"  or  starch  sugar. 
Levulose.  is  prepared  by  artificial  inversion  of  cane  sugar  with  mineral 
acids  or  invertase. 

Common  honey  is  a  mixture  of  dextrose,  levulose,  sucrose,  water, 
and  small  quantities  of  non-saccharine  matter;  the  levulose  is 
probably  formed  within  the  body  of  the  bee,  by  the  action  of  some 
enzyme,  which  inverts  the  sucrose  in  the  nectar  gathered  from  flowers 
by  the  insect. 

Dextrose  is  less  soluble  in  water  than  is  cane  sugar,  but  does  not 
crystallize  readily  from  solution.  When  crystallized  at  moderate 
temperatures,  it  contains  one  molecule  of  crystal  water;  but  from 
hot  water  or  from  alcohol  it  separates  in  the  anhydrous  state.  It  is 
a  little  more  than  half  as  sweet  as  sugar,  and  yields  an  anhydride, 
CeHioOs  (glycosan),  which  is  tasteless.  Dextrose  rotates  the  plane  of 
polarization  to  the  right  52.5°.  It  is  readily  fermentable,  and  reduces 
alkaline  copper  solutions  (Fehling's  solution).  It  occurs  in  nature  in 
combination  with  other  organic  substances,  forming  the  "  glucosides." 

Levulose  is  very  soluble  in  water,  but  crystallizes  from  alcohol 
without  crystal  water.  It  rotates  the  plane  of  polarization  of  the 
light  ray  very  strongly  to  the  left  (about  —  92°),  but  the  rotation  is 
variable  with  the  concentration  and  temperature.  It  also  reduces 
alkaline  copper  solution.  It  has  a  very  sweet  taste,  and  is  easily 
fermented  by  yeast. 

Maltose,  see  p.  449. 

Commercial  glucose  is  always  prepared  from  starch  as  the  cheap- 
est and  most  convenient  raw  material.  By  boiling  starch  paste  with 
mineral  acids,  it  is  converted  into  dextrin,  maltose,  and  dextrose,  the 
amount  of  the  last  depending  upon  the  time  of  the  boiling.  The 
acid  does  not  appear  to  enter  into  the  reaction,  but  merely  assists 
the  combination  between  the  starch  and  water,  by  which  the  glucose 
is  formed.  This-  is  a  process  of  "  hydrolysis."  It  might  be  repre- 
sented by  an  equation  :  — 

(C6H1005)n  +  nH20  =  n(C6H1206), 

but  this  does  not  represent  the  changes  which  actually  occur,  for  a 
number  of   intermediate   products  are  formed;    of  these,  the  dex- 


414 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


trin  is  never  entirely  converted  into  sugar,  some  remaining  unchanged 
in  the  commercial  glucose.  The  yield  of  dextrose  is  seldom  more  than 
85  or  90  per  cent  of  the  theoretical,  as  calculated  from  the  above 
equation.  The  best  conversion  is  obtained  with  hydrochloric  acid, 
which  is  generally  used  in  this  country,  but  in  Germany  sulphuric 
acid  is  used,  as  it  is  more  readily  separated  from  the  product.  In 
Europe  potato,  rice,  and  sago  starch  are  chiefly  used  for  glucose 
making,  but  in  this  country  corn  starch  is  exclusively  employed.  It  is 
used  "  green,"  and  is  prepared  on  the  premises.  The  corn  is  steeped 
from  3  to  5  days  in  water  at  150°  F.,  with  the  addition  of  250  gallons 
of  sodium  bisulphite  liquor  of  8°  Be.  to  each  2000  bushels  of  corn ;  the 
starch  is  then  prepared  as  described  on  p.  404. 

The  process  of  making  glucose  varies  slightly,  according  as 
syrup  or  solid  grape  sugar  is  to  be  the  final  product.  For  syrup, 
less  acid  is  used,  and  the  boiling  is  stopped  as  soon  as  a  test  with 
iodine  gives  a  port-wine  color.  This  may  leave  a  large  amount  of 
dextrin  in  the  product.  For  solid  dextrose,  the  boiling  is  continued 
for  a  short  time  after  alcohol  *  causes  no  precipitate  to  form  in  a  test 
portion  of  the  liquid. 

For  the  conversion,  the  starch  is  stirred  with  water  in  a  tub,  to 
form  a  "  milk  "  of  about  20°  Be.  Sometimes  a  part  of  the  acid  is 
added  to  this  milk,  and  the  mixture  warmed  to  about  38°  C.  It  is 
then  pumped  in  a  small  stream  into  the  boiling  dilute  acid  (1  to  3 
per  cent  acid)  contained  in  the  converter,  the  rate  of  inflow  being  so 
regulated  that  the  boiling  of  the  acid  liquid  is  not  interrupted. 

The  converter  may  be  an  open  vat  of  wood,  lined  with  lead,  and 
provided  with  stirring  apparatus  and  steam  coils.  But  open  con- 
verters are  now  abandoned  nearly  everywhere  in  favor  of  closed  con- 
verters (Fig.  114).  These 
v^  are  usually  made  of  cop- 

per or  gun  metal,  strong 
enough  to  withstand  a 
pressure  of  5  or  6  atmos- 
pheres. Steam  at  25  to 
30  pounds  pressure  is 
admitted  through  the 
perforated  copper  pipe 
(A).  The  starch  milk  is 
pumped  in  through  the 

FIG.  ii4.  copper  pipe  (B)  [the  di- 

*  Starch  and  dextrin  are  precipitated  by  alcohol,  but  dextrose  is  not, 


STARCH,   DEXTRIN,   AND   GLUCOSE 


415 


lute  acid  having  been  previously  introduced  through  (D)],  the  air 
vent  (V)  being  opened  at  this  time,  while  the  pressure  is  kept  at 
25  pounds.  As  soon  as  the  converter  is  full,  the  air  vent  is  closed, 
and  the  pressure  is  raised  to  30  pounds  for  about  50  minutes,  or  until 
the  iodine  test  shows  that  the  conversion  is  complete.  For  syrup, 
the  average  time  elapsing  from  the  beginning  of  the  starch  introduc- 
tion to  the  discharge  of  the  converter  is  about  1  hour  and  10  minutes, 
and  the  density  of  the  liquid  about  16°  Be. ;  for  grape  sugar,  about  an 
hour  and  a  half  is  necessary,  with  the  above  pressure  and  amount  of 
acid.  Conversion  is  also  carried  on  at  pressures  up  to  50  pounds  per 
square  inch,  with  corresponding  shortening  of  the  time  of  heating  to 
10  to  15  minutes. 

The  liquid  is  now  cloudy,  and  cannot  be  clarified  by  filtration. 
The  valve  (0)  is  opened,  and  the  liquid  is  blown  through  the  pipe  (C) 
into  the  neutralizer.  The  converter  is  provided  with  a  waste  pipe 
(F)  for  cleaning  purposes.  The  neutralizer  is  a  tank  (Fig.  115)  pro- 
vided with  an  effective  stirring  apparatus  (A,  A).  Immediately  after 
the  converter  liquid  has  been  received  into  the  neutralizer  it  is  treated 
with  sodium  carbonate 
solution,  *  introduced 
through  the  sprinkler 
(B),  to  remove  the  ex- 
cess of  acid.  It  is  left 
very  slightly  acid  to 
litmus,  a  pinkish  lilac 
color  being  about  right. 
If  made  alkaline,  the 
syrup  becomes  colored 
in  the  char  filtration, 
and  if  too  acid,  it  has  a 
turbid  appearance.  Much  of  the  dissolved  gluten  is  precipitated 
during  the  neutralizing,  and  forms  a  greenish  drab  scum. 

The  liquid,  called  "  light  liquor  "  is  run  through  bag  filters  to 
remove  suspended  impurities,  and  the  clear,  amber-colored  liquid  is 
then  run  through  bone-char  filters,  displacing  the  "  heavy  liquor  " 
for  which  the  filters  have  previously  been  used.  About  8000  gallons 
of  "  light  liquor  "  are  run  through  16  tons  of  bone-char,  which  has 
been  used  to  clarify  about  3500  gallons  of  "  heavy  liquor."  The 
filtrate  is  colorless,  or  faintly  amber-colored,  and  has  a  slightly  acid 

*  In  Europe  powdered  chalk  is  often  used  to  neutralize  the  sulphuric  acid,  the 
precipitate  of  calcium  sulphate  being  separated  from  the  liquor  by  filter-pressing. 


FIG.  115. 


416  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

reaction.  It  is  now  concentrated  in  a  triple-effect  evaporator  to  a 
density  of  27°  to  28°  Be.,  when  it  forms  the  "  heavy  liquor  "  above 
mentioned.  The  bone-char  in  the  filter  is  freshly  calcined,  dusted 
and  "  tempered  "  with  acid,  and  washed  with  water.  The  wash 
water  is  removed  by  compressed  air,  and  the  filter  is  filled  with 
the  heavy  liquor.  After  standing  about  an  hour,  the  outlet  pipe  is 
opened,  and  the  filtrate  runs  out  in  a  slow  stream,  while  more  unfil- 
tered  liquid  enters.  The  flow  is  secured  by  the  hydrostatic  pressure 
of  the  liquid  entering  the  filter  from  a  tank  elevated  above  it.  The 
filtrate  is  practically  colorless,  and  has  a  very  faint  odor.  It  is  con- 
centrated in  a  vacuum  pan  to  a  gravity  of  40°  to  44°  Be.  (1.375  to  1.43 
sp.  gr.).  During  this  evaporation  a  small  amount  of  a  solution  of 
sodium  bisulphite  (8°  Be.)  is  added  to  the  syrup  to  bleach  it,  and  to 
prevent  any  tendency  to  fermentation,  or  to  become  brown  when 
heated.  The  syrup,  composed  of  maltose,  dextrose,  and  dextrin,  is 
known  in  commerce  as  "  glucose  "  ;  the  name  "  grape  sugar  "  is  applied 
to  the  solid  product  obtained  by  carrying  the  conversion  further. 
Grape  sugar  forms  a  compact  mass  of  waxy  texture,  but  containing 
no  separate  crystals  of  dextrose. 

A  method  for  the  production  of  crystallized  glucose  (dextrose)  has 
been  devised  by  Behr,  in  which  a  concentrated  glucose  solution  is 
allowed  to  stand  at  about  35°  C.  in  contact  with  some  crystals  of  pure 
anhydrous  dextrose,  until  a  large  part  of  the  dextrose  separates  as  a 
mass  of  crystals.  By  running  through  a  centrifugal  machine,  the 
uncrystallized  syrup  is  thrown  off,  leaving  the  pure  crystals.  If 
glucose  is  dissolved  in  hot  concentrated  methyl  alcohol,  on  standing 
the  solution  deposits  crystals  of  pure  anhydrous  dextrose. 

The  bone-char  filters  *  used  for  glucose  are  cast-iron  cylinders, 
built  up  in  segments.  As  commonly  constructed  (Fig.  116)  one  holds 
about  16  tons  of  bone-black.  In  the  bottom  is  a  perforated  grating 
(A),  covered  with  burlap,  on  which  the  char  rests.  Beneath  this 
grating  is  the  outlet  pipe  (B),  which  is  carried  up  outside  the  filter 
to  the  level  of  the  top  of  the  char  when  the  filter  is  full.  By  this 
arrangement  no  liquor  flows  from  the  filter  until  the  char  is  entirely 
covered,  the  liquor  filters  slowly  and  with  less  tendency  to  form 
channels,  and  the  char  does  not  pack  nor  become  clogged.  On  one 
side,  near  the  bottom,  is  a  manhole  through  which  the  exhausted 
char  is  removed.'  In  the  top  is  another  manhole  for  introducing  the 
char,  and  also  an  inlet  pipe  (C)  for  the  liquid  to  be  filtered,  another 

*  Similar  filters  are  used  for  filtering  sugar,  oils,  etc.  In  large  sugar  refineries 
they  hold  from  30  to  40  tons  of  bone-black. 


STARCH,   DEXTRIN,   AND   GLUCOSE 


417 


(D)  for  steam,  and  an  air  vent  (E).  A  pipe  (G)  serves  for  the  introduc- 
tion of  compressed  air,  to  assist  in  forcing  the  liquor  or  wash  waters 
through  the  char  when  emptying  the 
filter,  and  for  running  off  the  over- 
flow of  wash  waters  when  boiling 
out  the  char.  A  branch  (F),  placed 
in  the  outlet  pipe  directly  below  the 
filter,  permits  connection  with  steam 
through  (H),  or  with  a  hot-water 
pipe  (J),  to  be  used  in  washing  the 
char;  it  also  connects  with  a  waste 
pipe  (L),  through  which  the  waste 
liquors  can  be  run  off.  The  inlet 
pipe  (C)  is  so  arranged  that  it  may 
be  connected  by  means  -of  a  rubber 
hose  with  the  pipes  supplying  the 
"light  liquors"  (N),  "heavy  liquors" 
(P),  wash  waters  (S),  or  tempering 
acid  (T).  The  outlet  pipe  (V)  is 
also  connected  in  the  same  way  with 
pipes  leading  to  the  storage  tanks  for  the  filtered  syrups  and  "  sweet 
water."  Below  the  lower  manhole  runs  an  endless  belt  which  receives 
the  spent  char  and  conveys  it  to  the  revivifying  kilns. 

The  bone-black  is  made  by  charring  bones  in  retorts,  and  then 
crushing  to  grains  about  2  or  3  mm.  in  diameter.  When  new,  it  has 
a  velvety  black  or  brownish  color,  and  often  contains  traces  of  tar 
and  other  impurities.  After  it  has  been  used  a  few  times,  the  grains 
become  rounded,  and  many  of  the  impurities  are  washed  away.  The 
syrup  first  run  through  the  filter  is  completely  decolorized  by  the 
action  of  the  char;  but  after  a  time  its  decolorizing  power  is 
impaired,  and  the  filtrate  begins  to  show  a  faint  yellow  color. 
Finally  it  runs  so  deeply  colored  that  no  advantage  is  gained  by 
filtration.  Then  the  light  liquor  remaining  in  the  filter  is  displaced 
by  water  (usually  condensed  water) ;  when  the  gravity  of  this  wash 
water  falls  below  10°  Be.,  it  is  collected  in  a  special  tank  as  "  sweet 
water,"  *  until  the  gravity  falls  to  1°  or  2°  Be.  Then  boiling  water  is 
introduced  through  (F)  at  the  bottom  of  the  filter,  and  run  out  through 
(G)  at  the  top,  and  then  to  the  sewer,  as  long  as  any  matter  can  be 
washed  out  of  the  char. 

*  The  "  sweet  water  "  is  used  to  wash  the  bag  filters,  or  it  is  added  to  the  "  light 
liquors," 

2E 


418  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

The  washed  char  is  drained,  and  then  "  steamed  down "  by 
steam  from  (D)  to  displace  the  wash  waters.  It  is  then  shovelled 
out  through  the  lower  manhole  on  to  the  conveyer,  and  carried  to  the 
kilns  where  it  is  revivified,  i.e.  its  decolorizing  power  is  restored  by 
destroying  the  adsorbed  coloring  matter  and  organic  impurities  by 
ignition  to  carbon.  It  is  dried  by  passing  over  tubes  heated  by  waste 
gases  from  the  furnace.  The  dry  char  passes  automatically  into 
narrow  vertical  retorts  of  cast-iron  kept  at  a  full  red  heat.  The  lower 
ends  of  these  retorts  project  below  the  furnace,  and  end  in  sheet-iron 
tubes  into  which  the  hot  char  passes,  and  is  cooled  before  it  is  exposed 
to  the  air.  At  the  bottom  of  each  tube  is  a  valve  which  automatically 
discharges  a  certain  quantity  of  the  char  at  regular  intervals  on  to  a 
belt  conveyer  running  below  the  kiln,  and  which  carries  the  revivi- 
fied char  to  revolving  reels,  where  it  is  sieved  to  remove  the  fine 
particles  before  returning  it  to  the  filter.  The  fine  char  ("  spent 
black  ")  falling  through  the  sieve  is  of  no  further  use,  and  is  sold  to 
the  fertilizer  maker.  In  order  to  replace  this  constant  waste  as  fine 
dust,  about  200  pounds  of  new  char  are  run  into  the  filter  with  each 
charge.  Much  new  char  at  a  time  is  undesirable,  since  the  tarry 
matters  in  it  tend  to  color  the  syrup.  After  revivifying,  the  char  is 
boiled  one-half  an  hour  in  the  filter  with  hydrochloric  acid ;  then  it 
is  drained  through  (F),  and  the  acid  washed  away  with  condensed 
water.  The  char  is  now  ready  for  use.  The  life  of  the  char  in 
glucose  making  is  about  3  months  of  continuous  service,  and  during 
that  time  it  is  revivified  about  once  in  every  3  or  4  days. 

Glucose  is  not  so  freely  soluble  in  cold  water  as  is  cane  sugar, 
nor  is  it  so  sweet.  When  the  glucose  is  to  be  used  for  syrup,  some 
manufacturers  have  tried  to  increase  its  sweetening  power  by  add- 
ing a  small  quantity  of  saccharine,  an  intensely  sweet  organic  sub- 
stance. But  this  is  probably  not  practised  to  any  great  extent. 

Considerable  discussion  relative  to  the  healthfulness  of  glucose 
as  a  food  has  been  aroused  at  times ;  but  when  properly  made,  it  is 
improbable  that  it  is  in  any  way  injurious  to  health. 

Dextrose  belongs  to  that  class  of  sugars  which  are  capable  of 
fermentation,  with  the  formation  of  alcohol,  'water,  and  carbon 
dioxide.  Because  of  this,  glucose  is  often  added  to  wine  and  beer 
wort  before  fermenting,  in  order  to  increase  the  percentage  of  alcohol 
in  the  beverage.  In  alkaline  solution,  glucose  has  a  very  strong  re- 
ducing action,  and  finds  some  use  in  the  arts  for  this  purpose ;  i.e. 
for  the  reduction  of  indigo  to  the  soluble  form  known  as  "  indigo 
white,"  in  the  dye  vat.  It  is  also  extensively  used  in  the  manufac- 


STARCH,   DEXTRIN,  AND  GLUCOSE  419 

ture  of  confectionery,  jellies,  preserves,  medicines,  and  table  syrups. 
Being  a  thick,  heavy  liquid,  glucose  syrup  is  much  used  as  a  thickening 
agent  in  many  industries  and  to  give  body  to  many  extracts  and 
decoctions  in  pharmacy.  Since  it  is  a  neutral  substance,  odorless 
and  colorless,  it  is  a  favorite  adulterant  for  thick  liquids,  such  as  ex- 
tracts of  logwood,  tannins,  and  natural  dyewoods. 

Sugars  can  be  made  from  cellulose  (CeHioOs)^  the  conversion  being 
effected  in  about  the  same  way  as  when  starch  is  used ;  but  it  is  more 
difficult  and  less  complete  with  dilute  acid  (see  Classen's  process 
p.  461). 

REFERENCES 

Die  Chemie  der  Kohlenhydrate.     R.  Sachsse,  Leipzig,  1877. 

Die  Starkefabrikation.     F.  Stohmann,  Berlin,  1879. 

Starch,  Glucose,  and  Dextrin.     Frankel  and  Hutter,  Philadelphia,  1881. 

Report  on  Glucose  by  the  National  Academy  of  Sciences  to  Commissioner 

of   Internal   Revenue.     Washington,    1884.     (Government  Printing 

Office.) 
Die  Starkefabrikation,  Dextrin-  und  Traubenzucker-fabrikation.     L.  von 

Wagner.     2te  Auf.     Braunschweig,  1886.     (Viaweg.) 
Die  Fabrikation  der  Starke,  des  Dextrins.     K.  Birnbaum,  Braunschweig, 

1887. 

Handbuch  der  Kohlenhydrate.     B.  Tollens,  Breslau,  1888. 
Manual  of  Sugar  Chemistry.     J.  H.  Tucker.     3d  ed.     New  York,  1890. 
Fabrication  de  la  Fecule  et  de  L'Amidon.     J.  Fritsch,  Paris,  1892  (?). 
Die  Starke-Fabrikation.     B.  von  Posanner,  Wien,  1894.     (Hartleben.) 
Die    Starke-Fabrikation    u.    die    Fabrikation    des    Traubenzuckers.     F. 

Rehwald.     3te  Auf.     Wien,  1895.     (Hartleben.) 
Zucker-  und  Starke-fabrjkation.     Otto. 
Essai  des  Farines.     Cauvert. 

Die  Fabrikation  der  Kartoffelstarke.  O.  Saare,  Berlin,  1897.  (Springer.) 
J.  Soc.  Chem.  Ind.,1909  (28),  343.  T.  B.  Wagner/  , 


CANE  SUGAR 


Sucrose  or  cane  sugar,  C^H^On,  is  found  in  many  plants,  but 
usually  in  association  with  other  substances  which  render  its  ex- 
traction difficult  and  unprofitable.  The  presence  of  dextrin,  glu- 
cose, "  invert  sugars  "  (dextrose  and  levulose),  and  dissolved  mineral 
salts  in  any  considerable  quantity  prevents  the  crystallization  of 
much  of  the  sucrose.  The  commercially  important  sources  of  sugar 
are  sugar  cane,  Saccharum  officinarum,  L.,  sugar  beet,  Beta  vulgaris, 
L.,  sugar  maple,  Acer  saccharium,  Wang.,  and  the  date  palm,  Phoenix 
dactylifera.  The  sorghum  plant,  Sorghum  vulgar  e,  Pers.,  contains 
considerable  sugar,  and  although  much  experimenting  has  been  done, 
owing  to  its  varying  content  of  sugar  and  its  large  percentage  of 
gums  and  dextrin,  it  does  not  afford  a  satisfactorily  crystallized  prod- 
uct. Maple  sugar  is  only  of  special  value  for  its  peculiar  flavor  as  a 
crude  sugar.  If  refined,  it  loses  this  characteristic  taste  and  is  not 
distinguishable  from  ordinary  cane  sugar.  Date  palm  sugar  is  pro- 
duced in  India  as  a  low-grade  crude  sugar  ;  it  is  known  as  "  jaggary  " 
and  is  shipped  for  refining. 

The  popular  term  "  sugar  "  was  originally  used  to  include  all 
substances  having  a  sweet  taste  ;  hence  the  names,  cane  sugar,  fruit 
sugar,  sugar  of  lead,  etc.  But  now  the  name  is  restricted  to  sucrose 
as  obtained  from  cane  or  beets.  The  chemical  term  "  sugar  "  includes 
a  large  class  of  bodies  belonging  to  the  carbohydrates.  Sucrose  is 
a  crystallized  body,  soluble  in  one-half  its  weight  of  cold  water,  and 
in  much  less  hot  water.  Its  specific  gravity  is  1.593.  It  forms 
salts  called  sucrates,  with  certain  metallic  bases,  such  as  potassium, 
calcium,  barium,  and  strontium,  and  on  this  fact  depends  the  use  of 
lime,  baryta,  and  strontia  for  recovering  sugar  from  molasses.  The 
sucrose  derived  from  the  various  sources  is  identical  in  all  cases, 
though  the  raw  sugars  differ  somewhat  in  flavor  and  color,  owing  to 
the  nature  of  the  impurities  they  contain. 

The  sugar  cane  and  sugar  beet  supply  nearly  all  the  sucrose 
of  commerce.  The  former  grows  only  in  those  climates  which  are 
warm  and  moist,  with  intervals  of  hot,  dry  weather  ;  the  most  of  the 
supply  comes  from  the  West  Indies,  the  Philippines,  Java,  the  Sand- 
wich Islands,  Brazil,  and  Louisiana.  Sugar  beets  thrive  best  in 
a  temperate  climate  and  are  extensively  raised  in  Germany  and 
France.  Extensive  experiments  in  raising  them  have  been  made  in 

420 


CANE   SUGAR 


421 


this  country,  and  there  seems  to  be  no  obstacle  in  the  way  of  climate 
or  soil  to  their  cultivation ;  in  Colorado,  California,  Michigan,  and  other 
states  sugar  beets  are  raised,  but  the  growth  of  the  industry  is  slow. 

In  the  growing  plant,  the  only  sugar  present  is  glucose,  the  sucrose 
not  being  secreted  until  the  plant  reaches  maturity.  Analysis  of  the 
ripe  cane  gives  the  following  average  :  — 

Sugar 18.% 

Fibre 9.5 

Water -   --    •    •    •    71. 

Analysis  of  the  ripe  cane  juice  shows :  — 

Water 80.% 

Sucrose 18. 

Glucose 0.30 

Gums  (Albuminoids) 1.40 

Mineral  Salts 0.30 

But,  owing  to  the  imperfect  extraction  of  the  juice,  and  to  losses 
during  its  evaporation  and  clarification,  the  actual  yield  of  sugar 
is  much  less  than  the  analysis  would  indicate.  Usually  from  16  to  20 
per  cent  of  the  juice  is  left  in  the  "  bagasse"  i.e.  the  waste  cane  pulp. 

The  preparation  of  raw  sugar  from  sugar  cane  may  be  considered 
under  four  heads :  (a)  extraction  of  the  juice ;  (b)  clarification ; 
(c)  evaporation ;  and  (d)  separation  of  the  crystals. 

(a)  Extraction.  —  The  cane  is  stripped  of  its  leaves  in  the  field 
and  taken  to  the  mill,  where  it  is  crushed  and  as  much  as  pos- 
sible of  the  juice  is  expressed.  This  must  be  done  soon  after  cut- 
ting, or  fermentation  begins 
and  much  sugar  is  lost.  The 
mills  (Fig.  117)  consist  of 
two  or  three  horizontal  rolls 
from  30  to  60  inches  in  di- 
ameter, so  set  that  their 
axes  are  parallel,  and  either 
at  the  vertices  of  an  isosceles 
triangle  (as  in  the  figure),  or 
in  the  same  perpendicular. 
The  rolls  are  set  in  adjust- 
able bearings.  When  there 
are  three  rolls,  the  cane  passes  between  the  top  roll  (T)  and  first 
bottom  roll  (B),  and  then  between  the  top  and  the  second  bottom 
roll  (D),  which  are  set  closer  together,  so  that  it  is  crushed  twice. 
It  is  usually  passed  through  two  or  three  mills,  and  about  60  or  70 


FIG.  117. 


422  OUTLINES   OF    INDUSTRIAL   CHEMISTRY 

per  cent  of  the  juice  extracted.  It  is  customary  in  Louisiana  to  use 
shredder  machines.  These  consist  of  toothed  wheels,  revolving  at 
different  speeds,  which  cut  and  break  the  cane  into  a  soft,  pulpy 
mass  before  it  goes  to  the  mills.  This  increases  the  yield  of  juice 
to  a  little  over  75  per  cent  of  the  total  content  of  the  canes.  The 
crushed  cane,  coming  from  the  extraction  mills,  is  generally  macer- 
ated in  about  10  or  12  per  cent  of  cold  or  hot  water,  to  which  a 
little  milk  of  lime  has  been  added,  and  is  then  again  passed  through 
the  mill.  This  gives  an  additional  increase  of  2  or  3  per  cent  in  the 
yield  of  juice.  The  expressed  juice  is  caught  in  a  trough  under 
the  mill  and  is  run  off ;  the  bagasse  or  "  trash  "  is  burned  under  the 
boilers.  The  furnace  must  be  large  and  a  forced  draught  is  used  to 
keep  them  white  hot. 

Diffusion  methods  for  extracting  cane  juice,  similar  to  those  used 
for  sugar  beets  (p.  425),  but  at  a  temperature  of  90°  C.,  have  been 
tried,  but,  excepting  on  a  few  plantations  in  Louisiana,  with  no  great 
success,  since  the  refuse  needs  much  handling  and  drying  before  it 
can  be  burned,  and  an  abundant  supply  of  water  is  necessary. 

(6)  The  bits  of  cane  floating  in  the  juice  when  it  comes  from  the 
mills  are  removed  by  straining  through  wire  screens.  The  juice 
also  contains  organic  acids,  nitrogenous  bodies,  and  invert  sugar  in 
solution,  which  are  very  susceptible  to  fermentation.  To  remove 
these,  the  juice  is  defecated.  It  is  passed  through  a  heater,  placed 
in  the  vapor  pipe  of  the  vacuum  pan,  and  then  into  the  defecator 
tanks,  which  are  heated  by  a  steam  coil.  Here  milk  of  lime  is  added 
in  such  proportions  that  the  acids  are  almost  neutralized  and  the 
juice  left  very  slightly  acid  to  litmus.  The  lime,  aided  by  the  heat, 
coagulates  the  albumin  and  precipitates  lime  salts  of  organic  acids, 
which  serve  to  adsorb  the  gums,  but  very  little  of  the  color.  The 
liquid  is  rapidly  heated  to  boiling,  which  causes  the  coagulum  to 
rise  as  a  scum,  usually  about  2  inches  thick  and  holding  all 
the  suspended  impurities  mechanically  entangled  in  it.  After 
standing  one-half  an  hour  or  an  hour,  the  scum  begins  to  crack 
and  is  skimmed  off ;  or  the  juice  is  drawn  off  from  beneath  it.  The 
scum  is  run  into  scum  tanks,  where  it  is  mixed  with  more  lime  and  with 
sawdust  to  assist  in  the  subsequent  filter-pressing  by  making  the  cake 
more  porous.  The  filtrate  is  mixed  with  the  juice  from  which  the  scum 
is  decanted,  and  the  whole  is  then  ready  for  evaporation. 

Calcium  acid  phosphate  is  sometimes  used  instead  of  lime  for 
defecation,  but  not  generally.  The  juice  contains  gummy  matter 
and  other  impurities,  which  interfere  with  the  crystallization  of  the 


CANE   SUGAR  423 

sugar  somewhat,  but  they  cannot  be  removed  entirely,  since  no 
cheap,  non-poisonous  material  is  known  that  will  coagulate  all  the 
gums.  Defecation  is  probably  the  most  important  step  in  sugar 
making,  since  on  its  successful  working  depends  in  a  great  measure 
the  amount  and  quality  of  the  sugar  produced. 

(c)  The  process   of   evaporation  of  the  juice   has   been   greatly 
improved  in  recent  years  in  the  larger  sugar  houses.     By  the  old 
method  it  is  boiled  down  in  open  pans  until  the  mass  begins  to  "  grain," 
i.e.  to  crystallize,  and  then  it  is  emptied  into  shallow  tanks  where  it  is 
stirred  while  cooling.     The  mixture  of  crystallized  sugar  and  molasses 
is  then  filled  into  hogsheads ;   holes  are  bored  through  the  ends  of  the 
casks,  which  are  then  placed  on  end,  in  a  rack,  for  several  weeks,  and 
the  molasses  allowed  to  drain  out  into  a  receptacle  underneath.     The 
holes  are  then  plugged  and  the  hogshead  of  sugar  is  sent  to  market. 
The  best  grades  of  sugar  made  in  this  way  are  called  muscovado;  they 
are  light  brown  in  color  ancl  contain  from  87  to  91  per  cent  of  sucrose. 
This  process  is  now  but  little  used,  and  only  in  the  less  progressive 
countries.     Probably  no  planter  can  derive  any  profit  from  muscovado 
sugars  in  the  present  state  of  the  industry ;    there  is  too  much  invert 
sugar  produced,   together  with  coloring  matter  formed  during  the 
boiling.     Low-grade  sugars  are  produced  in  this  way,  especially  the 
jaggary  sugars.     The  molasses  from  muscovado  sugar  was  formerly 
used  as  table  syrup,  and  some  is  still  so  used.     Concrete  sugars  are 
made  by  evaporating  the  juice  directly  to  a  hard  mass  in  a  special  pan 
called  a  "  concretor,"  no  attempt  being  made  to  separate  the  crystals 
from  the  molasses.     In  all  the  more  modern*  sugar  houses,  the  juice  is 
evaporated  in  vacuum  pans.     It  is  generally  concentrated  in  a  triple- 
effect  apparatus,  until  the  solution  contains  about  50  per  cent  solids, 
and  the  separation  of  crystals  is  about  to  begin.     It  is  then  trans- 
ferred to  a  simple  vacuum  pan,  called  the  "  strike  pan,"  where  the 
evaporation  is  continued  slowly  under  high  vacuum ;    the  object  is  to 
build  up  the  crystals  on  the  crystal  points. 

(d)  When  the  grain  has  reached  the  desired  size,   the  mixture 
of  crystals  and  syrup,  which  is  called  "  masse-cuite,"  is  emptied  into 
storage  tanks,  where  it  cools  somewhat.     It  is  then  run  into  cen- 
trifugal machines  which  separate  the  molasses  from  the  sugar.     The 
latter  is  called  the  "  first  sugar  "  and  is  at  once  packed  for  market. 
When  of  good  quality,   these  centrifugal   sugars   are  light  colored 
and  contain  95  to  97  per  cent  pure  sugar.     Sometimes  the  juice  is 
treated  with  sulphur  dioxide  in  the  defecators,  and  the  sugar,  which 
is  then  nearly  white,  is  called  "  plantation  granulated." 


424 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


SYNOPSIS    OF    RAW    SUGAR    MAKING    FROM    SUGAR   CANE 

Cutting  and  Stripping  in  Cane  field 

I 
(Shredders)  MiUs 

1 


36  to  40  per  cent  Bagasse 

I 


Furnaces 


to  70  per  cent  Juice 

I 
Defecators 

I 


Bag  Filters  or 
Filter-presses 


Scum 

I 
Filter-press 

I 


I  I 

Press  Liquor       Press  Cake 


Multiple  Effect 

I 
Strike  "  Vacuum  Pan 

I 
Centrifugals 


First  Molasses 

I 
(Defecators) 

I 
Vacuum  Pans 


I 
First  Sugar 


If  "  boUed  blank  " 

I 

Wagons  to  "  Hot  Room  "  or  to 
crystallizers  (3  to  7  days) 


If  "  boiled  to  grain  " 


Centrifugals 


I 

Second  Molasses  Second  Sugar 

|  fRum 

Used  for  <  Feeding  Cattle 
[Fuel 

The  molasses  separated  from  the  first  sugar  is  called  first 
molasses  and  contains  45  to  50  per  cent  of  sucrose.  It  is  diluted 
and  defecated  with  lime  or  with  calcium  acid  phosphate,  and  the 
clarified  syrup  is  reboiled  in  the  vacuum  pans  to  obtain  a  "  second 


CANE   SUGAR  425 

sugar."  This  is  slow  to  crystallize,  and  the  concentrated  syrup  is 
allowed  to  stand  from  3  to  7  days  in  a  room  kept  at  a  tempera- 
ture of  60°  C.,  until  the  crystallization  is  complete.  The  mass  is 
then  "  centriffed,"  yielding  a  "  second  "  or  "  molasses  "  sugar,  and 
"  second  "  molasses.  This  sugar  is  of  variable  quality,  and  may 
be  sent  to  market  for  what  it  will  bring,  or  it  may  be  dissolved 
in  water  and  the  syrup  added  to  the  juice  going  to  the  vacuum  pan. 

The  second  molasses  contains  about  40  per  cent  sugar,  which  it 
does  not  pay  to  recover.  It  is  sometimes  fermented  for  making 
rum  or  alcohol ;  or,  since  it  contains  a  high  percentage  of  carbona- 
ceous matter,  it  is  often  injected  into  the  furnace  in  a  fine  stream, 
where  it  has  a  certain  fuel  value.  A  small  amount  is  used  for  feed- 
ing cattle.  It  is  not  suitable  for  use  as  a  table  syrup  or  for  culinary 
purposes;  but  a  small  amount  of  the  first  molasses  is  used  in  this 
way. 

The  preparation  of  raw  sugar  from  beets  is  an  extensive  indus- 
try in  Europe.  It  consists  in  the  following  operation :  (a)  wash- 
ing and  slicing  the  beets;  (6)  extracting  the  juice;-  (c)  clarifying 
it;  (dj  evaporating  it;  (e)  separating  the  crystals;  (/)  treating 
the  molasses. 

(a)  The  beets  are  washed  in  long  troughs,   each  containing  a 
revolving  shaft  which  carries  pins  set  in  the  form  of  a  screw.     These 
push  the  beets  along  against  a  stream  of  water  flowing  through  the 
trough,  and  by  rubbing  them  against  each  other,  loosens  the  sand 
and  loam,  which  are  carried  away  by  the  water.     The  beets  are  then 
cut  into  slices,  from  0.5  to  1  mm.  thick,  by  a  machine  containing 
revolving  knives. 

(b)  The  juice  is  now  usually  extracted  from  the  sliced  beets  by 
the  diffusion  process.     The  chips  are  put  into  vertical  iron  cylinders, 
and  systematically  digested  with  water  at  a  temperature  of  80°  C. 
The  digesters  are  arranged  in  batteries  of  ten,  and  between  each  two 
is  a  "  juice  warmer  "  or  "  calorisator,"  to  maintain  the  temperature 
of  the  apparatus.     These  are  similar  in  construction  to  the  econo- 
mizer of  a  Feldmann's  apparatus  (p.  152),  and  consist  of  narrow  brass 
pipes  surrounded  by  a  steam  jacket.     When  the  chips  are  exhausted, 
they  are  removed,  the  digester  refilled  and  made  the  last  of  the  series. 
Fresh  water  is  admitted  to  the  tank  containing  the  most  nearly  ex- 
hausted chips,  and  passes  into  the  others  in  succession,  finally  leaving 
that  most  recently  filled,  as  a  sugar  solution  containing  nearly  as  much 
sucrose  as  does  the  original  beet  sap ;   all  but  0.5  per  cent  of  the  sugar 
is  extracted.     About  150  parts  sugar  solution  are  obtained  for  every 


426  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

100  parts,  by  weight,  of  beets.  The  spent  chips  are  rich  in  nitrog- 
enous matter  and  are  often  pressed  and  dried  for  cattle  food ;  or  they 
are  returned  to  the  field  for  fertilizing. 

The  process  of  diffusion  depends  upon  osmosis.  When  the  vege- 
table cell  is  surrounded  by  water,  or  by  a  sugar  solution  of  less  density 
than  is  the  sap,  the  sugar  and  other  crystallizable  substances  are  dis- 
placed by  the  water  and  pass  through  the  cell  walls,  while  the  colloid 
bodies  (gums,  albuminoids,  etc.)  are,  for  the  most  part,  retained  by 
the  membrane.  Thus  the  juice  obtained  by  diffusion  is  much  purer 
than  that  obtained  by  other  means. 

Sometimes  the  beets  are  rasped  to  a  soft  pulp  in  machines  simi- 
lar to  those  used  in  making  starch  from  potatoes.  The  juice  is  then 
expressed  in  hydraulic  presses  or  between  rolls. 

In  the  maceration  process  the  rasped  pulp  is  systematically  lixiv- 
iated with  water,  while  in  other  methods  centrifugal  machines  are 
used  to  extract  the  juice. 

(c)  The  juice  is  clarified  in  the  same  way  as  that  from  sugar  cane. 
After  passing  through  a  sieve  to  remove  floating  dirt,  the  juice  is 
defecated  with  lime.  As  it  is  nearly  free  from  invert  sugar  and  glu- 
cose, an  excess  of  lime  may  be  used  without  injury  to  the  sugar.  If 
heated  with  glucose  present,  lime  colors  the  product  more  or  less  brown 
or  yellow.  In  defecating,  the  lime  neutralizes  the  organic  acids  and 
in  conjunction  with  heat  coagulates  albumin  and  mucus.  Excess  of 
lime  is  removed  by  the  "  carbonation  process,"  or  saturation,  in  which 
carbon  dioxide  in  excess  is  forced  into  the  neutralized  liquor;  this 
decomposes  any  insoluble  calcium  sucrate,  thus  preventing  loss  of  sugar. 
The  carbonation  is  carried  on  in  two  or  three  stages,  to  avoid  re-solu- 
tion of  the  lime  (as  bicarbonate) ;  the  first  treatment,  at  about  90°  C., 
continues  until  the  alkalinity  (as  calcium  oxide),  shown  by  titration, 
is  about  0.1  per  cent.  After  filter-pressing  the  liquor  is  again  saturated 
at  about  100°  C.,  with  the  carbon  dioxide,  until  the  alkalinity  is  re- 
duced to  from  0.01  to  0.02  per  cent. 

Sulphur  dioxide  gas  is  often  introduced  along  with  the  carbon  diox- 
ide, or  a  third  saturation  with  sulphur  dioxide  alone  may  be  used. 
This  is  always  used  when  making  white  sugars.  Sulphur  dioxide  has 
some  decolorizing  action  on  the  juice,  and  seems  to  precipitate  certain 
lime  salts  not  removed  -by  the  carbon  dioxide.  The  saturated  juice  is 
filtered  again  to  remove  precipitated  matter  carried  down  with  the 
calcium  carbonate. 

After  the  final  saturation,  the  clarified  juice  should  retain  very 
slight  alkalinity,  to  avoid  tendency  to  inversion  of  the  sucrose  by  the 


CANE   SUGAR  427 

heat ;   but  too  much  >lime  causes  slow  formation  of  crystals  during  the 
evaporation  in  the  vacuum  pan. 

(d)  The  evaporation  of  the  clarified  juice  is  carried  on  in  two 
stages,  by  the  use  of  triple  effects  and  a  strike  pan,  much  in  the 
same  way  as  is  that  from  sugar  cane.     The  syrup  may  be  "  boiled  to 
grain,"  in  which  case  sugar  crystals  are  formed  in  the  strike  pan ;    or 
it  is  "  boiled  blank,"  by  which  a  clear,  thick  liquid  is  obtained,  which 
deposits  sugar  crystals  on   cooling.     The  first  method  is  generally 
employed  and  gives  the  largest  yield  of  sugar ;   but  a  very  pure  syrup 
is  required. 

(e)  The  mixture  of  molasses  and  sugar  is  separated  in  centrifugal 
machines  as  described  on  p.  423.     The  raw  sugar  so  obtained  is  similar 
to  the  first  sugar  from  cane.     The  molasses  is  boiled  down  for  a  second 
sugar  and  second  molasses;    the  latter  contains  40  to  50  per  cent  of 
sucrose  and  large  amounts  of  colloidal  organic  substances  and  potas- 
sium salts,  which  prevent  crystallization  of  the  sugar.     The  organic 
matter  consists  in  part  of  nitrogenous  bodies  (amines?),  which  impart 
an  unpleasant  odor  and  taste,  rendering  the  molasses  unfit  for  table 
use. 

(/)  The  molasses  is  nearly  free  from  dextrose  and  levulose  and  the 
recovery  of  much  of  its  sucrose  by  chemical  treatment  thus  becomes 
feasible.  Three  methods  of  treatment  are  in  use  :  — 

The  Steffens'  process,  using  lime,  depends  on  the  formation  of  an 
insoluble  calcium  sucrate,  possibly  C^H^On  •  3  CaO,  which  precip- 
itates while  the  non-sugar  substances  remain  in  solution.  Pow- 
dered quicklime  is  slowly  stirred  into  the  cold  (below  15°  C.),  diluted 
molasses,  until  a  test  shows  an  excess  has  been  added  over  the  amount 
needed  to  precipitate  all  the  sugar.  The  magma  is  filter-pressed,  the 
press-cake  washed  with  cold  water,  and  then  used  instead  of  lime  for 
defecating  the  fresh  juice.  When  treated  with  carbon  dioxide,  calcium 
carbonate  is  precipitated  and  the  sugar  is  left  in  solution. 

Scheibler's  strontium  process,  much  used  in  Europe,  depends  on 
the  formation  of  insoluble  di-strontium  sucrate  (C^H^Ou  •  2  SrO), 
which  precipitates.  A  hot  (70°  C.)  concentrated  solution  of  strontium 
hydroxide,  amounting  to  about  2  J  times  the  weight  of  the  sugar  in  the 
molasses,  is  mixed  with  the  hot  molasses  and  stirred  vigorously,  while 
raising  the  temperature  to  boiling;  the  di-sucrate  separates  from  the 
hot  liquor  and  is  rapidly  filtered  in  bag-filters,  and 'washed  with  hot 
strontium  hydroxide  solution.  The  crystals  are  dissolved  in  cold 
strontium  hydroxide  liquor  and  the  solution  cooled  below  10°  C. ; 
after  several  days  a  large  part  of  the  strontium  sucrate  decomposes, 


428  OUTLINES   OF    INDUSTRIAL   CHEMISTRY 

separating  strontium  hydroxide  as  crystals  and  leaving  the  sugar  with 
some  strontium  hydroxide  in  solution.  The  liquor,  decanted  from  the 
crystals,  is  saturated  with  carbon  dioxide,  precipitating  all  the  stron- 
tium as  carbonate,  and  leaving  a  pure  sugar  solution.  The  strontium 
carbonate  is  calcined  to  the  oxide  and  returned  to  the  process.  Simi- 
lar processes  employing  barium  hydroxide  and  sulphide  have  also  been 
used  abroad. 

The  osmosis  process  depends  on  dialysis,  the  mineral  salts  passing 
through  parchment  paper  membranes  more  rapidly  than  the  sugar. 
The  apparatus  resembles  a  filter-press,  the  compartments  separated 
by  parchment  paper;  the  alternate  compartments  are  filled  with 
molasses  and  water,  heated  to  about  90°  to  100°  C.  The  salts  pass 
into  the  water  and  some  water  passes  into  the  molasses;  the  two 
liquids,  being  kept  in  circulation  through  the  several  cells,  finally  flow 
from  the  apparatus  as  diluted  and  purified  molasses  and  a  solution  of 
salts.  The  molasses  is  reboiled  to  crystallize  part  of  its  sugar.  The 
water  may  be  evaporated  to  recover  potash  salts,  but  often  goes  to 
waste. 

SUGAR  REFINING 

Raw  sugar  derived  from  any  source  is  more  or  less  deeply  colored 
and  impure,  and  must  be  refined  to  yield  the  pure  white  sugar  for 
consumption.  It  would  seem  that,  on  economical  grounds,  the  refin- 
ing should  be  done  at  or  near  the  place  where  the  sugar  is  produced. 
But  at  present  the  refineries  are  not  in  the  same  countries  that  pro- 
duce the  raw  sugar;  indeed,  they  exist  solely  to  remedy  the  errors 
and  careless  work  of  the  raw-sugar  maker,  or  to  circumvent  unfavor- 
able import  duties  levied  on  the  refined  sugar. 

Sugar  refining  is,  in  theory,  a  simpler  process  than  the  prepara- 
tion of  the  raw  sugar,  but  it  requires  great  care  and  attention  to  de- 
tail, as  well  as  much  expensive  machinery.  It  consists  in  dissolving 
the  crude  material,  separating  the  impurities,  and  recrystallizing  the 
sugar.  A  refinery  needs  a  frontage  on  navigable  water  and  ample 
dock  and  storage  sheds.  An  abundant  water  supply  for  condensers, 
or  washing  purposes, .  for  melting  the  sugar,  and  for  boiler  use  is 
absolutely  necessary.  A  large  refinery,  capable  of  treating  900  tons 
of  sugar  per  day,  will  use  about  1,700,000  gallons  of  water  daily ;  of 
this,  about  1,000,000  gallons  are  used  in  the  condensers  of  the  vacuum 
pans.  The  next  largest  consumption  is  in  washing  the  char  filters. 

On  the  ground  floor  of  the  refinery  are  the  melting  tanks,  in  each 
of  which  usually  16,000  pounds  of  sugar  can  be  dissolved,  to  form  a 


CANE   SUGAR  429 

syrup  of  1.25  sp.  gr.>  and  containing  55  per  cent  solids.  If  a  cen- 
trifugal *  or  superficially  colored  raw  sugar  is  to  be  used,  it  is  first 
dumped  into  elevators  which  carry  it  to  the  washing  plant.  There 
it  is  mixed  with  a  syrup  and  some  cold  water,  and  the  thick  magma 
passed  into  centrifugal  machines,  where  the  syrup,  carrying  most  of 
the  superficial  coloring  matter  and  some  of  the  glucose,  gums,  and 
dirt,  is  thrown  off.  This  leaves  the  raw  sugar  about  99  or  99J  per 
cent  pure;  it  is  then  sent  to  the  melter.  The  syrup  goes  to  the 
melter  later,  and  is  mixed  with  a  lower  grade  of  sugar. 

The  melter  is  heated  by  closed  steam  coils,  contains  an  efficient 
stirring  apparatus,  or  mixer,  and  has  a  false  bottom,  to  retain  coarse 
impurities,  such  as  straw,  bits  of  cane,  leaves,  sticks,  and  stones. 
In  starting  the  day's  work,  it  is  customary  to  begin  with  the  purest 
sugar,  e.g.  the  centrifugal,  and  after  a  certain  amount  of  this  has 
been  dissolved  and  pumped  away,  to  melt  a  less  pure  sugar,  e.g.  the 
muscovado ;  then  the  temperature  is  raised,  and  molasses  and  poor 
concrete  sugars  are  put  into  the  melter ;  next  come  the  syrups  from 
washing  the  raw  sugar,  together  with  various  syrups  from  the  refin- 
ing process ;  these  are  followed  by  the  various  scums  and  "  sweet 
waters  "  (wash  waters)  of  the  refining. 

The  melter  is  filled  about  one-third  full  of  water  at  170°  F.,  the 
stirrer  put  in  motion,  and  the  first  charge  of  sugar  dumped  in ;  after 
15  minutes  it  is  dissolved,  and  the  liquor,  varying  in  color  from  a  light 
straw  color  to  dark  brown,  is  pumped  directly  to  the  "  blow-ups." 

The  blow-URS  are  defecators,  capable  of  holding  one  melt  (16,000 
pounds  of  sugar).  They  are  heated  by  closed  steam  coils,  and  each 
has  a  perforated  coil,  through  which  air  is  forced  to  agitate  the 
liquor.  The  temperature  is  kept  at  160°  F.,  for  centrifugal  sugars, 
but  lower  grades  must  have  more  heat.  This  defecation  is  intended 
to  remove  the  gums,  organic  acids  and  impurities  (amines,  etc.),  artd 
any  fine  suspended  dirt.  The  materials  used  are  lime,  alum,  clay, 
blood,  or  other  form  of  albumin,  soluble  phosphates,  and  often  fine 
bone-char.  Sugars  which  contain  but  little  glucose  will  bear  a  large 
quantity  of  lime,  without  risk  of  darkening  the  color.  Liquid  blood 
is  often  used,  about  4  gallons  being  necessary  for  each  blow-up. 
The  coagulated  blood  rises  to  the  top  as  a  scum,  entangling  the 
impurities,  which  are  thus  separated  from  the  liquor.  Soluble  cal- 
cium phosphate  (acid  phosphate)  is  now  much  used  instead  of  blood, 
the  amount  being  about  one-half  of  one  per  cent  of  the  weight  of  the 

*  Centrifugal  sugars,  as  distinguished  from  concrete  or  muscovado  sugars,  are 
those  from  which  the  molasses  has  been  separated  by  the  use  of  centrifugal  machines. 


430  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

sugar.  The  mixture  is  agitated  for  about  20  minutes,  and  then  ex- 
actly neutralized  with  lime,  when  a  flocculent  precipitate  separates, 
carrying  with  it  the  gums  and  suspended  matter  by  adsorption. 

After  the  defecating  material  has  been  added,  the  temperature  is 
raised  to  212°  F.,  and  the  air  blast  turned  on  for  about  20  to  30  min- 
utes. When  a  numbef  of  deep  cracks  appear  in  the  scum,  the  reaction 
is  ended,  and  the  liquor  is  drawn  off. 

From  the  blow-ups  the  defecated  liquor  passes  into  bag  filters, 
from  which  the  filtrate  must  run  perfectly  clear,  or  the  sugar  will 
not  be  white.  The  bags  are  similar  to  those  described  on  page  15. 
They  are  suspended  in  a  closed  room,  about  12  by  6  by  8  feet,  fitted 
with  an  open  steam  coil,  by  which  the  bags  are  heated  to  180°  F.  be- 
fore the  liquor  is  allowed  to  run  into  them.  The  first  runnings  are 
muddy,  and  are  refiltered.  When  it  runs  clear,  the  liquor  is  col- 
lected in  tanks  placed  above  the  char  filters.  The  bags  finally 
become  clogged  with  mud,  which  is  very  slimy,  and  the  filtration  is 
very  slow,  but  is  usually  allowed  to  continue  for  about  twenty  hours. 
Then  the  bags  are  flushed  with  "  sweet  water,"  which  is  drawn  out 
by  a  suction  pipe,  and  returned  to  the  defecators.  The  bags  are 
then  flushed  with  hot  water,  until  the  liquor  draining  from  them 
contains  only  2  per  cent  of  solids.  They  are  then  turned  inside  out, 
in  a  tank  of  hot  water,  to  wash  off  the  soft  mud,  and  are  finally  thor- 
oughly washed  with  clean  water  and  dried. 

The  mud  washed  from  the  bags  contains  about  20  per  cent  sugar 
and  is  sent  to  special  tanks,  where,  after  further  dilution  with  water, 
lime  is  added  until  the  liquor  is  strongly  alkaline,  when  it  is  filter- 
pressed.  The  clear  liquor  from  the  filter-press  is  used  to  flush  the 
bag  filters  and  to  mix  with  the  melting  water  for  raw  sugar.  The 
mud  in  the  filter-press  is  washed  with  hot  water,  the  wash  waters, 
constituting  the  "  sweet  waters,"  being  used  for  diluting  and  flush- 
ing. The  mud,  still  containing  about  2  per  cent  of  sugar,  which  it 
does  not  pay  to  recover,  is  thrown  away. 

The  clear,  straw-colored  liquor  from  the  bag  filter  is  now  run  into 
the  char  filter.  These  are  similar  to  those  used  for  glucose  (Fig.  116, 
p.  417),  but  are  larger,  averaging  24  feet  deep  and  8  feet  in  diameter. 
The  bone-char  is  in  grains,  which  pass  a  No.  16  sieve,  but  remain  on 
a  No.  30  sieve.  Finer  grains  clog  the  filter,  and  coarser  ones  have 
less  action  on  the  coloring  matter  in  the  syrup.  The  char  is  washed 
with  hot  water  before  the  liquor  is  run  in,  but  it  is  not  "  tempered  " 
with  acid,  as  is  the  case  in  glucose  filtering.  About  1  pound  of  char 
is  used  for  each  pound  of  sugar  melted,  and  it  takes  6  hours  to  fill 


CANE   SUGAR  431 

the  filter  before  the  .filtrate  begins  to  run.  After  revivifying,  the 
char  enters  the  filter  at  about  150°  F.,  and  the  liquor  is  filtered  at  the 
same  temperature.  After  some  time  the  filter  becomes  clogged,  and 
it  is  often  necessary  to  use  compressed  air  to  force  the  liquor  through 
the  char.  At  first  the  liquor  is  water  white,  but  later  it  becomes  col- 
ored, and  finally  the  char  is  "  spent,"  and  must  be  revivified.  The 
char  is  washed  with  hot  water,  and  the  wash  waters  are  saved  until 
they  contain  only  2  per  cent  of  solids ;  below  this  they  are  thrown 
away.  This  cleansing  of  the  char  requires  about  20  hours.  It  is 
then  revivified,  as  described  on  page  418. 

The  revivifying  process  causes  the  pores  of  the  char  to  become 
slowly  clogged  with  vegetable  carbon,  which  seems  to  have  no  decolor- 
izing action.  By  passing  the  spent  char  through  a  rotary  kiln  to 
which  a  limited  amount  of  air  is  admitted,  the  vegetable  carbon  can 
be  more  or  less  destroyed  before  the  animal  carbon  is  attacked ;  thus 
the  usefulness  of  the  char  can  be  considerably  prolonged.  The  aver- 
age life  of  the  char  is  about  three  years  in  sugar  refining. 

In  Germany,  bone-char  is  but  little  used,  since  pure  beet  sugar  is 
produced  directly  from  the  juice  after  defecation. 

The  filtered  liquor  then  goes  to  the  vacuum  pans,  which  are  of 
copper,  about  12  feet  high  and  10  feet  in  diameter,  a  "  goose-neck  " 
connecting  each  pan  with  the  condenser.  A  pan  full  of  syrup  is 
called  a  "  skipping."  For  granulated  sugar,  the  syrup  is  run  in 
until  the  steam  coil  is  covered,  and  the  boiling  is  carried  on  at  160°  F., 
until  grains  appear;  then  more  syrup  is  added,  slowly,  and  the 
grains  grow  until  the  desired  size  is  reached.  Tests  are  taken  from 
time  to  time,  by  means  of  the  "  proof  stick,"  a  solid  brass  rod  pass- 
ing through  a  stuffing  box  and  projecting  into  the  interior  of  the 
pan.  In  one  side  of  the  rod,  near  the  inner  end  is  a  small  cavity, 
about  one-half  inch  deep.  When  the  rod  is  pulled  out  until  this 
cavity  is  outside  the  stuffing  box,  2  or  3  cubic  centimeters  of  syrup 
mixed  with  crystals  are  obtained.  Thus  small  samples  are  readily 
obtained  at  any  time,  without  interrupting  the  vacuum ;  and  from 
the  appearance  of  these  samples,  the  sugar-boiler  judges  of  the  prog- 
ress of  the  evaporation.  The  time  required  to  complete  the  process 
is  from  2  to  3  hours. 

When  the  grain  is  large  enough,  the  vacuum  pumps  are  stopped 
and  air  is  slowly  admitted  to  the  pan.  The  bottom  valve  is  then 
opened,  and  the  magma  of  sugar  and  syrup  drops  into  coolers,  or 
mixers,  directly  beneath,  and  is  stirred  while  cooling,  to  prevent  the 
grains  agglomerating.  The  sugar  and  syrup  are  separated  in  cen- 


432 


OUTLINES   OP   INDUSTRIAL   CHEMISTRY 


SUGAR   REFINING 

Raw  Sugar  Warehouse 

I 
Elevators 

.1 
Mixers 

Centrifugals 


1 

Sugar                          Centrif.  1 
I 
Bins                                     Me 

iVashings 
ter 

1 
Melters                                Blov 
I 

r-ups 

1 
Blow-ups                               Bag 
1 

liters 

Bag  filters 

I 

Scums  ("  Mud  ") 

I 

Washing  free  from 
sugar  liquor 

I 

Removing  mud 
from  bags 
I 


Liquor 


Heating  tanks 

I 
Bone-black  ("  Char  ")  Filters 


Mud  blow-ups  Washing     bags 

|  for  next  day's 

Filter-press  use 

I 


Dry  mud 


I 

Thin  liquor, 
put  to  various 
uses 


Washing  liquors     Vacuum  pans 
from  Char  | 

| Mixers 

r       ~~i 

Thin  liquor      Char  to 

|  Kilns 

Triple  effect  Centrifugals 


r     ~| 

Heavy  liquor     Syrup  Sugar 

I  I  J 

Returned  to     Reboiled         Bins 

Char  filter      for  sugar  j 

|          Granulator 
Centrifugals 
|  Bolter 

r  ~~i 

Barrel  syrup  Soft  sugar  | 

Barrels 

trifugal  machines.  The  former  is  washed  in  the  centrifugal,  to 
remove  adhering  syrup,  and  is  then  dropped  into  a  storage  bin,  from 
which  it  is  carried  by  a  belt  conveyer  to  the  granulator.  This  is  a 
long,  rotating  cylinder  of  iron,  set  at  a  slight  incline,  and  heated  by 


CANE   SUGAR 


433 


steam.  By  passing  through  this  hot  tube,  the  sugar  is  thoroughly 
dried,  while  the  rotation  prevents  the  grains  sticking  together.  It 
then  passes  through  a  series  of  sieve  reels,  which  usually  separate 
the  grains  into  three  or  four  sizes,  the  commercial  sizes  being  packed 
in  barrels  for  market. 

The  syrup  from  the  centrifugals  is  reboiled  with  more  fresh  syrup, 
or,  if  its  color  is  too  deep  for  this,  it  is  sent  back  to  the  char  filter, 
after  which  it  is  boiled  to  grain  for  soft  sugars,  the  temperature  in  the 
vacuum  pan  being  110°  to  125°  F.  These  soft  sugars  are  "  centriffed," 
but  not  put  through  the  granulator,  and  are  boiled  to  a  finer  grain 
than  is  the  granulated.  In  many  cases  they  are  redissolved  and  con- 
verted into  granulated  sugars.  The  syrup  from  them  is  amber 
colored  or  brown,  and  is  barrelled  for  table  syrup  or  for  manufacturing 
purposes. 

AVERAGE  ANALYSIS  OF  SUGARS 


RAW  SUGAR 

CANE 
SUGAR 

GLUCOSE  * 

WATER 

ORGANIC 
MATTER 

ASH 

Good  centrifugal   .     . 

96.0 

1.25 

1.00 

1.25 

0.50 

Poor  centrifugal    . 

92.0 

2.50 

3.00 

1.75 

0.75 

Good  muscovado  .     .     fc 

91.0 

2.25 

5.00 

1.10 

0.65 

Poor  muscovado    .     .     ., 

82.0 

7.00 

6.00 

3.50 

1.50 

Molasses  sugar      .    -.    --. 

88.0 

2.80 

3.00 

3.50 

2.70 

Jaggary  sugar  .      .     4  -  . 

75.0 

11.00 

8.00 

4.00 

2.00 

Manila  sugar   .... 

87.0 

5.50 

4.00 

2.25 

1.25 

Beet  sugar,  1st      ... 

95.0 

0.00 

2.00 

1.75 

1.25 

Beet  sugar,  2d       ... 

91.0 

0.25 

3.00 

3.25 

2.50 

REFINED  SUGAR 

Granulated  sugar       .     . 

99.8 

0.20 

0.00 

0.00 

0.00 

White  coffee  sugar-    .    •. 

91.0 

2.40 

5.50 

0.80 

0.30 

Yellow  XC  sugar      /    . 

87.0 

4.50 

6.00 

1.50 

1.00 

Yellow  sugar     .     . 

82.0 

7.50 

6.00 

2.50 

2.00 

Barrel  syrup                .    '. 

40.0 

25.00 

20.00 

10.00 

5.00 

The  loaf  sugar  of  commerce  is  made  by  running  the  magma  of 
syrup  and  fine  crystals  from  the  vacuum  pan  into  conical  moulds 
where  it  is  allowed  to  stand  for  some  time.  A  further  crystalliza- 
tion of  sugar  takes  place  which  cements  the  grains  together,  while 
the  uncrystallized  syrup  drains  off  through  a  small  hole  opened 
in  the  point  of  the  cone.  A  little  water  is  poured  on  the  surface  of 
the  sugar,  and,  percolating  down  through  the  mass,  displaces  any 

*  The  term  "  glucose  "  includes  sugars  which  reduce  Fehling's  solution,  but  are 
not  necessarily  optically  active. 
2F 


434  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

syrup  remaining.  This  draining  is  slow,  and  it  is  now  customary  to 
place  several  of  the  cones  in  a  centrifugal  machine,  with  their  points 
towards  the  outside  of  the  drum.  The  syrup  and  wash  waters  are 
forced  through  the  mass,  which  is  left  as  a  dry,  hard  conical  lump, 
the  "  sugar  loaf  "  of  trade. 

REFERENCES 

A  Treatise  on  the  Manufacture  of  Sugar  from  the  Sugar  Cane.     Peter 

Soames,  London,  1872.     (Spon  &  Co.) 

Guide  pratique  du  Fabricant  de  Sucre.     N.  Basset,  3  vols.,  Paris,  1875. 
Manuel  pratique  de  Diffusion.     Elie  Fleury  et  Ernst  Lemaire,  Paris,  1880. 
The  Sugar  Beet.     L.  S.  Ware,  Philadelphia,  1880.     (Baird  &  Co.) 
Manual  of  Sugar  Chemistry.     J.  H.  Tucker,  New  York,  1881. 
Die  Zuckerarten  und  ihre  Derivate.     E.  von  Lippmann,  Braunschweig, 

1882. 
Traite  theorique  et  pratique  de  la  Fabrication  du  Sucre.     Paul  Horsin- 

Deon,  Paris,  1882.     (Bernard  et  Cie.) 
Report  on  Sorghum  Sugar  by  a  Committee  of  the  National  Academy  of 

Science,  Washington,  1883. 
Lehrbuch  der  Zuckerf abrikation.     K.  Stammer.     2te  Auf .     Braunschweig, 

1887. 

Handbuch  der  Kohlenhydrate.     B.  Tollens,  Breslau,  1888. 
Sugar.     A  Handbook  for  Planters  and  Refiners.     C.  G.  W.    Lock  and 

B.  E.  R.  Newlands  and  J.  A.  R.  Newlands,  London,  1888.      (Spon.) 
Die  Zuckerriibe.     H.  Briem,  Wien,  1889. 

Manuel  Pratique  du  Fabricant  de  Sucre.     P.  Boulin,  Paris,  1889. 
A  Guide  to  the  Literature  of  Sugar.     H.  L.  Roth,  London,  1890. 
Handbuch  der  Zuckerfabrikation.     4te  Auf.     F.  Stohmann,  Berlin,  1899. 
Introductory  Manual  for  Sugar  Growers.     F.  Watts,  London,  1893. 
Die  Zuckerfabrikation.     B.  von  Posanner,  Wien,  1894. 
Le  Sucre  et  1' Industrie  sucriere.     Paul  Horsin-Deon,  Paris,  1894. 
Handbook  for  Sugar  Manufacturers  and  their  Chemists.     G.  L.  Spencer. 

3d  ed.     New  York,  1897.     (Wiley  &  Sons.) 
Handbook  for  Chemists  of  Beet-sugar  Houses  and  Seed-culture  Farms. 

G.  L.  Spencer,  New  York,  1897.     (Wiley  &  Sons.) 
The  Technology  of  Sugar.     J.  G.  Mclntosh,  1903. 
Cane  Sugar  and  the  Process  of  its  Manufacture.     Geerligs,  2d  ed.,  1909. 
Calculations  used  in  Cane-sugar  Factories.     I.  H.  Morse,  1904. 
Die  Zucker-Fabrikation.     H.  Classen,  Magdeburg,  1904.     (Schallehn  u. 

Wollbriick.) 

Manuel-Guide  de  la  Fabrication  du  Sucre.     R.  Teyssier,  Paris,  1904. 
Beet  Sugar  Manufacture.     H.  Claassen.    Trans,  by  W.  T.  Hall  and  G.  W. 

Rolfe,  New  York,  1906.     (Wiley.) 
Beet  Sugar  Manufacture  and  Refining.    2  vols.    L.  S.  Ware,  New  York, 

Cane  Sugar.    Noel  Deerr,  Manchester,  1911.     (Rodger.) 


FERMENTATION   INDUSTRIES 

Fermentation  is  a  general  term  applied  to  various  chemical  changes 
caused  by  the  action  of  bodies  called  ferments.  These  are :  (a)  Un- 
organized chemical  substances,  called  enzymes,  secreted  by  living 
cells  ;  and  (b)  certain  micro-organisms.  Enzymes  include  such  bodies 
as  diastase,  invertase,  pepsin,  ptyalin,  emulsin,  etc.  They  usually 
assist  in  the  nutritive  functions  of  the  animal  or  plant  in  which  they 
occur,  the  changes  which  they  cause  being  sometimes  of  the  nature  of 
hydrolysis.  Buchner  has  isolated  from  the  expressed  liquid  of  com- 
minuted yeast  cells,  an  enzyme  called  Zymase,  which  changes  sugar  into 
alcohol,  without  the  presence  of  the  yeast  plant  itself.  This  indicates 
that  the  change  of  the  sugar  is  not  directly  connected  with  the  life 
functions  of  the  plant,  and  the  enzyme  acts  as  a  catalyzer.  Micro- 
organisms cause  complex  changes  in  the  substance  on  which  they  act, 
due  in  part  to  the  enzymes  which  they  secrete.  The  product  formed 
varies  with  the  kind  of  organism  predominating  in  the  liquid,  and  the 
fermentation  is  designated  as  alcoholic,  acetic,  lactic,  butyric,  etc. 

Organized  vegetable  ferments  are  (1)  Mould  growths ;  (2)  Yeast 
plants  (Saccharomycetes) ;  (3)  Bacteria  (Schizomycetes). 

These  are  all  capable  of  growth  and  reproduction,  and  associated 
with  the  former  are  the  chemical  changes  called  fermentation  and 
putrefaction.  It  is  generally  true  that  alcoholic  fermentation  is 
caused  by  the  yeasts,  while  putrefactive  fermentation  is  due  to 
bacteria  ;  but  there  are  some  exceptions. 

Organized  ferments  may  be  reproduced  by  microscopic  spores, 
which  propagate  when  introduced  even  in  small  quantities  into  a 
fermentable  liquid,  and  cause  the  chemical  change  of  a  large  part  of 
it.  Consequently  these  spores,  floating  in  the  dust  in  the  air,  find 
their  way  into  fermenting  liquids  which,  when  freely  exposed  to  the 
air,  may,  therefore,  contain  many  kinds  of  ferments. 

The  moulds  are  threadlike  plants,  devoid  of  chlorophyl,  and 
forming  a  somewhat  felted  mass  called  the  mycelium.  They  grow 
readily  upon  fruit,  damp  wood,  wet  grain,  or  on  the  walls  of  damp 
cellars  and  similar  places,  forming  greenish,  bluish,  or  gray  vegeta- 
tions, which  emit  a  characteristic  musty  odor.  They  exert  an  oxidiz- 
ing action  upon  organic  matter  and  hydrolyze  starch.  Since  they 
develop  musty  or  sour  odors  and  taste  in  the  nutrient  medium,  destroy 
sugars,  and  often  form  coloring  matter,  they  are  injurious  in  ferment- 

435 


436  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

ing  processes.  But  their  presence  is  mainly  due  to  negligence  and  lack 
of  cleanliness  and  proper  ventilation. 

The  bacteria,  splitting  ferments,  Schizomycetes,  are  microscopic 
plants  of  the  lowest  order,  forming  rods,  or  spiral,  threadlike,  or 
rounded  cells.  These  propagate  by  fission  with  astounding  rapidity, 
if  the  conditions  are  favorable;  if  not,  some  forms  develop  spores, 
which  may  be  exposed  to  extreme  cold  or  to  moderately  high  tem- 
perature without  losing  their  power  of  germinating  when  brought 
into  a  proper  medium.  These  spores  are  scattered  everywhere,  in  the 
soil,  the  air,  and  water;  being  very  minute,  they  are  transported  by 
every  puff  of  wind,  and  thus  readily  find  access  to  liquids  and  moist 
substances  exposed  to  the  air.  For  their  nutriment  and  progagation 
they  need  about  the  same  substances  and  condition  of  temperature 
as  the  yeasts  (see  below).  They  cause  oxidation  and  decomposition, 
and  often  putrefaction,  in  many  bodies  containing  albuminous  and 
nitrogenous  material,  and  the  products  of  these  reactions  are  some- 
times extremely  poisonous.  Some  of  them  cause  acute  diseases  in 
man  and  in  animals.  Many  of  the  "  diseases  "  of  wine  and  beer,  as 
well  as  acetic,  lactic,  butyric,  and  other  fermentations,  are  caused  by 
them.  Also  the  production  of  nitrates  and  nitric  acid  in  the  soil 
(p.  146)  is  attributed  to  the  action  of  bacteria. 

Bacteria  are  much  more  susceptible  to  the  action  of  antiseptic 
substances  than  are  the  yeasts,  but  heat  and  cold  affecj  them  less. 
Thus  the  process  of  Pasteurization  (p.  442)  is  not  a  sure  protection 
against  their  action. 

The  yeasts,  Saccharomycetes,  have  great  technical  importance, 
owing  to  the  part  they  take  in  alcoholic  fermentations.  Several 
species  are  recognized,  each  playing  some  particular  role  in  the  fer- 
mentation. Thus  Saccharomyces  cerevisice  is  the  particular  ferment 
for  beer;  S.  ellipsoideus  is  the  chief  organism  present  in  fermenting 
wine,  and  in  any  spontaneous  fermentation  of  fruit  juices. 

Yeast  consists  of  an  aggregation  of  plant  cells,  forming  a  slimy, 
yellow  mass  of  peculiar  odor,  and  having  an  acid  reaction.  Under 
proper  conditions,  the  cells  propagate  with  great  rapidity.  The  tem- 
perature must  be  constant  at  from  6°  to  26°  C.,*  and  substances 
necessary  for  the  growing  plant  must  be  present;  these  are  a  fer- 
mentable sugar,  nitrogenous  matter,  and  certain  mineral  salts,  such 
as  phosphates  and  sulphates  of  calcium,  potassium,  or  magnesium. 
Air  (oxygen)  is  desirable,  especially  at  first ;  later  it  is  often  ex- 
cluded to  prevent  secondary  fermentations,  by  which  the  alcohol 

*  A  higher  temperature  is  conducive  to  the  formation  of  fusel  oil. 


FERMENTATION    INDUSTRIES  437 

formed  is  converted,  into  acetic  acid  or  other  products.  Through 
alcoholic  fermentation  the  fermentable  substance  in  the  liquor  is 
converted  into  alcohol  and  carbon  dioxide :  — 

C6H1206  =  2  C2H5OH  +  2  CO2. 

But  this  does  not  express  the  true  decomposition,  for  a  large  num- 
ber of  other  substances  are  formed  at  the  same  time,  the  more  im- 
portant being  glycerine,  succinic  acid,  butyl,  isobutyl,  and  amyl 
alcohols  (fusel  oil),  and  various  organic  ethers.  Owing  to  these  sec- 
ondary reactions,  the  yield  of  alcohol  is  somewhat  reduced. 

When  the  amount  of  alcohol  formed  in  the  liquid  equals  14  to  15 
per  cent,  the  yeast  can  no  longer  propagate  itself,  and  the  fermenta- 
tion ceases.  The  presence  of  certain  mineral  salts,  such  as  borax, 
mercuric  chloride,  sulphurous  acid,  and  free  caustic  alkalies,  often 
retards  or  prevents  fermentation. 

The  fermentable  substance  in  the  liquid  to  be  fermented  with 
yeast  is  generally  a  sugar,  dextrose  being  the  most  readily  converted ; 
and  it  is  quite  possible  that  other  sugars  are  first  changed  to  glucose 
before  the  real  fermentation  begins.  For  example,  cane  sugar  is  not 
in  itself  readily  fermented,  but  by  the  action  of  the  invertase  secreted 
by  the  yeast,  it  is  converted  (hydrolyzed)  into  dextrose  and  levulose, 
which  are  readily  fermented.  The  invertase  is  not  destroyed  in  this 
hydrolysis,  ^  and  hence  there  is  scarcely  any  limit  to  the  amount  of 
cane  sugar  which  may  be  hydrolyzed  by  a  small  quantity  of  inver- 
tase. Maltose,  C^H^On,  is  also  readily  converted,  by  yeast,  into 
fermentable  dextrose,  and  thence  into  alcohol  and  carbon  dioxide ; 
or,  perhaps  the  maltose  is  fermented  directly,  without  the  interme- 
diate formation  of  dextrose.  Starch  is  not  capable  of  direct  alcoholic 
fermentation,  but  must  first  be  converted  into  fermentable  sugar. 
This  conversion  is  easily  accomplished  by  the  action  of  diastase, 
which  changes  the  starch  into  maltose. 

Yeasts  are  also  grouped  in  two  general  classes,  viz. :  top  yeasts 
and  bottom  yeasts.  The  former  require  rather  high  temperature  (15° 
to  30°  C.)  for  the  fermentation,  which  is  very  active,  the  rapid  evo- 
lution of  carbon  dioxide  causing  the  liquid  to  bubble  violently,  and 
carrying  the  yeast  to  the  surface.  This  yeast  is  used  for  heavy  ales 
and  beer,  for  alcohol  and  high  wines,  and  for  some  wine.  Bottom 
yeast  acts  at  a  lower  temperature  (4°  to  10°  C.),  and  the  fermentation 
is  slow;  the  evolution  of  carbon  dioxide  is  gradual,  and  the  yeast 
remains  on  the  bottom  of  the  vat. 

The  researches  of  Pasteur,  Reess,  Hansen,  and  others  have  thrown 


438  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

much  light  on  the  nature  and  properties  of  the  yeasts.  Hansen 
divides  the  Saccharomyces  into  six  typical  species,  as  follows :  — 

Saccharomyces  cerevisioe,  —  the  beer  ferment  most  commonly  em- 
ployed in  breweries  and  distilleries.  It  may  be  a  top  yeast,  i.e.  float- 
ing on  the  surface  of  the  fermenting  liquid,  or  a  bottom  yeast,  according 
to  the  conditions  existing  during  the  fermentation. 

Saccharomyces  Pastorianus  I.,  —  a  beer  ferment  which  causes  an 
unpleasant  bitter  taste  in  beer.  It  is  a  bottom  yeast,  remaining  on 
the  bottom  of  the  vat  during  the  fermentation. 

Saccharomyces  Pastorianw  II.,  —  a  top  yeast  found  in  beer,  but 
which  appears  to  have  no  action  upon  it. 

Saccharomyces  Pastorianus  III.,  —  a  beer  ferment  causing  cloudi- 
ness and  disease  in  the  beer.  It  is  a  top  yeast,  resembling  the  last  two. 

Saccharomyces  ellipsoidew  I.,  —  a  bottom  yeast,  the  true  wine  fer- 
ment. It  occurs  on  the  grapes. 

Saccharomyces  ellipsoideus  II.,  —  a  yeast  causing  the  cloudiness  in 
turbid  beer.  It  is  a  bottom  yeast,  and  resembles  the  last  mentioned 
above. 

In  addition  to  the  above,  Hansen  also  isolated  from  a  brewer's 
yeast  two  varieties,  known  as  Carlsberg  Nos.  1  and  2,  and  closely 
resembling  S.  cerevisia?.  No.  1  yields  a  beer  with  less  carbon  diox- 
ide than  No.  2,  and  is  mainly  employed  for  bottle  beers ;  No.  2  is 
used  for  export  beers. 

All  these  yeasts  ferment  glucose,  sucrose  after  inversion,  and 
maltose,  but  not  lactose.  Other  yeasts  are  known  which  ferment 
sucrose,  but  not  maltose,  and  still  others  which  contain  no  invertase, 
and  will  not  ferment  sucrose* 

For  technical  purposes,  it  has  long  been  the  custom  to  use  culti- 
vated yeasts  for  alcoholic  fermentation ;  but  Pasteur  showed  that 
these  contain  many  "  wild  yeasts,"  i.e.  plants  whose  nature  and  ac- 
tions were  either  unknown,  or  are  detrimental  to  the  product.  Han- 
sen reasoned  from  his  observations  on  the  effect  produced  by  the 
eight  above-described  yeasts,  that  for  a  uniform  quality  of  product 
there  must  be  exactly  the  same  kind,  or  kinds,  of  yeast  employed  in 
each  brew.  Hence  he  devised  his  system  of  pure  yeast  cultures, 
obtained  in  sterilized  nutrient  material  by  propagation  from  a  single 
plant.  Thus  a  single  variety  of  yeast  is  obtained,  by  the  use  of 
which  the  fermentation  is  more  easily  controlled. 

In  fermentations  at  a  high  temperature,  where  the  amount  of 
alcohol  formed  is  near  the  maximum,  the  yeast  plant  generally  dies ; 
but  by  low  temperature  fermentation  the  propagation  of  the  plant 


FERMENTATION   INDUSTRIES  439 

may  be  controlled  and  the  variety  kept  unchanged  through  a  con- 
siderable period  of  time;  a  sufficient  amount  of  carefully  selected 
yeast  is  preserved  for  the  next  liquor  to  be  fermented.  But  in  some 
cases,  a  fresh  lot  of  yeast  is  especially  prepared  each  time. 

There  are  three  purposes  for  which  the  alcoholic  fermentation  is 
carried  on  technically  :  (a)  for  the  manufacture  of  the  yeast ;  (6)  for 
the  carbon  dioxide  formed ;  (c)  for  the  alcohol. 

The  first  of  these  is  usually  associated  with  the  third,  and  con- 
sists in  growing  a  pure  yeast  free  from  wild  yeast  and  other  fer- 
ments. The  process  of  growth  is  carefully  watched  by  the  aid  of 
the  microscope,  and  the  appearance  of  any  injurious  variety  con- 
demns the  whole  lot. 

Those  most  generally  cultivated  are  the  S.  ceremsioe  and  S.  ellip- 
soideus.  The  cells  are  filtered  out  of  the  liquid  in  which  they  are 
grown,  by  fine  sieves,  usually  of  bolting  cloth,  and  are  washed  with 
cold  water,  filter-pressed,  and  the  cake  heavily  pressed.  It  is  then 
mixed  with  from  25  to  50  per  cent  of  starch  or  flour  and  brought 
into  market  as  "  compressed  yeast."  By  drying  at  a  low  tempera- 
ture the  plant  retains  its  vitality  for  the  most  part,  and  will  grow 
when  put  into  a  fermentable  solution. 

The  liquid  from  which  the  yeast  cells  have  been  filtered  is  some- 
times allowed  to  ferment  further  until  the  action  ceases ;  it  is  then 
distilled  for  alcohol.  The  yeasts  are  grown  in  a  filtered  extract  of 
malt,  and  since  they  require  free  access  of  oxygen  for  their  greatest 
development,  it  is  now  customary  to  force  a  blast  of  sterilized  air 
through  the  fermenting  liquid.  This  hastens  the  process  and  in- 
creases the  yield  of  yeast,  but  decreases  the  formation  of  alcohol  so 
that  its  recovery  is  unprofitable. 

At  a  low  temperature,  compressed  yeast  will  keep  for  a  long  time ; 
but  in  warm,  moist  air  it  rapidly  decomposes  or  develops  mould 
growths.  Dried  yeast  is  less  active  than  the  compressed,  but  will 
bear  exposure  to  the  air  and  can  be  kept  for  a  longer  period.  The 
chief  use  of  commercial  yeast  is  for  bread  making. 

Fermentation  for  the  carbon  dioxide  is  practically  confined  to  the 
manufacture  of  bread.  In  this  a  mixture  of  flour  and  water  is  al- 
lowed to  ferment.  The  nitrogenous  matter  in  the  flour  furnishes 
nutriment,  and  the  starch  is  partly  converted  into  fermentable  sugar 
by  the  ferments  always  present  in  the  flour  and  yeast.  A  vigorous 
alcoholic  fermentation  begins,  liberating  a  considerable  volume  of 
carbon  dioxide,  which,  being  retained  by  the  pasty  dough,  causes  the 
whole  mass  to  swell  and  become  porous.  When  bread  dough  is 


440  OUTLINES    OF   INDUSTRIAL   CHEMISTRY 

baked,  the  heat  kills  the  yeast,  stopping  all  fermentation,  and  at  the 
same  time  evaporates  off  the  alcohol,  and  finally  it  hardens  the 
gluten,  dextrin,  and  starch  paste,  retaining  the  porous  structure  in 
the  mass. 

Fermentation  for  the  alcohol  may  take  place  without  the  addi- 
tion of  prepared  yeast,  as  in  the  case  of  most  wines ;  but  the  germs 
of  the  ferment  are  then  derived  from  the  air  or  are  present  upon  the 
skins  of  the  fruit,  and  so  when  the  latter  is  crushed  they  are  mixed 
with  the  juice.  In  all  cases,  however,  where  starch  is  to  be  con- 
verted into  alcohol,  malt  and  yeast  are  employed. 

WINE 

Wine  is  fruit  juice  which  has  undergone  an  alcoholic  fermenta- 
tion; it  is  most  commonly  made  from  grapes.  The  fermentation  is 
spontaneous  and  progresses  without  special  attention  until  the  sugar 
has  been  converted  to  alcohol.  The  fermentable  sugars  in  grape 
juice  are  dextrose,  levulose,  and  some  inosite ;  when  fully  ripe,  it 
contains  on  an  average  18  per  cent  of  fruit  sugar,  in  addition  to 
tartaric  acid  (as  potassium  bitartrate),  malic  acid,  a  little  butyric 
acid,  albuminoids,  non-nitrogenous  matter,  and  ash.  All  these  vary 
in  quantity  according  to  the  kind  of  grape  and  the  nature  of  the  soil 
and  climate.  The  grape  skins  contain  tannin  (CuHioOg),  oils,  and 
(except  in  white  grapes)  coloring  matter  (oenocyanin).  These  all 
pass  into  the  juice  when  the  grape  is  pressed. 

The  character  of  the  soil  in  which  the  vine  grows  influences  the 
fruit  materially.  It  must  be  light  and  porous,  and  contain  salts 
of  potas§ium,  lime,  magnesium,  iron,  and  sodium,  especially  sul- 
phates, phosphates,  chlorides,  and  silicates.  Decomposed  volcanic 
rock,  such  as  granite  and  lava,  appear  to  furnish  the  best  soil.  A 
warm  summer  with  only  a  moderate  amount  of  rain  is  essential  for 
a  high  percentage  of  sugar  in  the  juice,  and  the  highest  percentage 
is  usually  obtained  in  October  in  latitude  near  40°.  If  the  grapes 
are  allowed  to  hang  until  overripe,  the  amount  of  sugar  decreases 
somewhat,  but  the  wine  sometimes  has  a  peculiar  bouquet  which  is 
much  prized. 

When  ripe,  the  grapes  are  carefully  picked  and  sometimes  sorted 
into  several  grades.  For  the  finest  wines  they  are  removed  from  the 
stems,  since  these  contain  an  excess  of  tannin  and  tartaric  acid. 
They  are  crushed  between  wooden  rolls  or  by  pounding  in  mortars, 
or  by  treading  with  the  bare  feet.  The  juice  is  extracted  by  press- 
ing, or  better  in  centrifugal  machines.  It  is  called  "  must  "  and  con- 


FERMENTATION   INDUSTRIES  441 

tains  the  soluble  matter  of  the  grape.  The  quality  of  the  wine  de- 
pends in  a  great  measure  on  the  ratio  of  the  sugar  to  the  free  acids 
(tartaric  and  malic).  The  most  favorable  ratio  is  1  part  of  acid  to 
29  parts  of  sugar,  but  the  average  is  about  1  to  16. 

For  red  wines  it  is  customary  to  allow  a  partial  fermentation  of 
the  mash  before  pressing  out  the  juice.  The  alcohol  thus  formed 
extracts  the  coloring  matter  from  the  skins  more  thoroughly  than  it 
can  be  directly  expressed.  White  wine  is  made  from  white  grapes, 
or  from  juice  which  has  been  separated  from  the  marc  before  fer- 
mentation. 

Through  the  action  of  the  wine  ferment,  Saccharomyces  ellipsoideus, 
present  on  the  grape  and  in  the  air  of  grape-producing  regions,  fer- 
mentation begins  in  the  must  at  once.  It  takes  place  in  two  stages : 
the  active  fermentation,  which  lasts  from  one  to  three  weeks ;  and  the 
still  fermentation,  continuing  for  several  months.  The  former  takes 
place  in  open  vats  or  tubs  at  a  moderate  temperature  (10°  to  30°  C.). 
It  may  be  a  "  bottom  fermentation,"  where  the  temperature  is  from 
10°  to  15°  C.,  or  a  "  top  fermentation  "  at  20°  C.  or  above.  The  for- 
mer is  generally  practised  in  northern  Europe  and  produces  wines 
low  in  alcohol  but  having  a  fine  aroma  or  "  bouquet."  Top  fermen- 
tation, which  is  more  rapid,  seldom  lasting  more  than  a  week,  is  car- 
ried on  in  southern  Europe,  and  yields  wine  high  in  alcohol  but  lack- 
ing bouquet. 

In  a  few  hours  after  being  put  into  the  fermenting  vats  the  clear 
must  becomes  turbid  and  acquires  a  sour  taste  and  smell ;  soon  a 
rapid  evolution  of  carbon  dioxide  begins  and  a  froth  forms  on  the 
surface.  Some  manufacturers  expose  the  must  freely  to  the  air  and 
stir  it  frequently  to  aerate  it,  but  others  exclude  the  air  as  much  as 
possible.  A  moderate  amount  of  aeration,  especially  at  first,  is 
doubtless  beneficial ;  but  towards  the  end  of  the  active  fermentation 
too  much  air  admission  may  introduce  the  acetic  ferment,  Bacterium 
aceti.  During  this  fermentation  the  albuminoids  are  largely  con- 
sumed by  the  growing  yeast.  Finally  the  active  fermentation  be- 
comes slow  and  the  must  is  now  known  as  "  new  wine."  It  is  drawn 
into  closed  tubs  or  casks  which  are  filled  quite  full  and  the  opening 
loosely  closed  to  prevent  the  access  of  the  acetic  ferment.  Here  the 
still  fermentation  takes  place,  the  time  depending  largely  upon  the 
temperature  of  the  fermenting  cellar;  the  lower  the  temperature, 
the  less  rapid  the  fermentation.  The  yeast  settles,  and  as  the  alco- 
hol content  increases,  a  crystallization  of  acid  potassium  tartrate, 
together  with  some  calcium  salts  and  coloring  matter,  takes  place, 


442  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

forming  as  a  deposit  called  argol ;  this  is  the  source  of  the  "  cream 
of  tartar  "  of  commerce. 

When  it  has  become  clear,  and  nearly  the  whole  of  its  sugar  con- 
tent has  been  converted  into  alcohol,  the  wine  is  drawn  off  into  large 
casks.  The  bungs  -are  closed  and  the  wine  allowed  to  "  ripen  "  for 
perhaps  two  or  three  years.  During  this  process,  which  is  essentially 
an  oxidation,  the  albuminoids  and  tannins  are  largely  precipitated, 
together  with  some  of  the  coloring  matters  and  other  impurities. 
At  the  same  time  the  higher  alcohols  or  fusel  oil  formed  during  the 
fermentation  combine  with  the  free  acids  present  to  form  organic 
ethers  which  impart  the  peculiar  flavors  to  wines.  In  order  to  hasten 
the  ripening  process,  the  wine  is  frequently  drawn  off  from  the  casks 
and  a  little  gelatine,  isinglass,  milk,  blood,  or  albumin  added  each 
time.  This  forms  a  precipitate  which  drags  down  the  fine  suspended 
matter.  Gelatinous  silicic  acid,  kaolin,  gypsum,  or  plaster  of  Paris 
are  also  used  for  this  clarifying.  The  last  two,  however,  react  with 
the  tartrate  of  potassium  always  present  in  the  wine,  forming  potas- 
sium sulphate  and  precipitating  calcium  tartrate.  The  former  re- 
mains in  the  wine,  and  since  it  has  an  injurious  action  on  the  human 
system,  the  use  of  plaster  and  gypsum  is  prohibited  in  some  coun- 
tries. When  the  ripening  process  is  complete,  the  wine  is  bottled 
and  is  ready  for  consumption. 

The  use  of  pure  cultures  of  yeast  for  the  fermentation  of  wine 
has  recently  been  introduced  with  good  results,  yielding  products 
which  ripen  more  readily  and  have  good  keeping  qualities. 

Wine  is  subject  to  various  "  diseases  "  due  to  bacteria  and  other 
ferments.  Sourness  is  caused  by  an  acetic  fermentation  due  to  too 
much  exposure  to  the  air.  Ropiness  is  the  result  of  mucus  fermen- 
tation. Stale  or  flat  taste  and  bitterness  are  produced  by  a  peculiar 
fungus  or  plant  growth.  These  troubles  may  be  prevented  by  care 
in  handling  the  wine,  attention  to  cleanliness,  and  by  always  keep- 
ing the  casks  full  to  prevent  the  entrance  of  air.  Any  shrinkage 
through  evaporation  or  leakage  should  be  replaced  with  more  wine 
at  once.  Those  diseases  which  are  caused  by  ferments  can  usually 
be  remedied  in  the  early  stages  by  heating  the  wine  to  about  70°  C., 
which  kills  most  of  the  injurious  germs  and  renders  the  wine  capa- 
ble of  long  keeping  and  transportation.  This  process,  called  Pasteur- 
izing, does  not  injure  the  aroma  and  other  qualities.  It  is  carried 
out  by  immersing  the  bottled  wine  in  hot  water,  or  by  running  the 
wine  from  the  cask  through  long  pipes  placed  in  tanks  of  hot  water. 

Other  methods  of  improving  the  keeping  qualities  of  wine  are  the 


FERMENTATION   INDUSTRIES  443 

addition  of  salicylic  or  boric  acid,  but  these  are  considered  injurious 
to  health  and  are  prohibited  in  some  countries.  A  general  practice 
is  to  fume  the  casks  with  sulphur  dioxide  and  to  wash  them  with 
sodium  bisulphite  solution  before  filling  with  wine.  Sometimes  sul- 
phurous acid  is  added  to  the  wine  to  act  as  a  preservative. 

Wine  made  from  grape  juice  as  it  is  expressed  from  the  fruit  is 
rarely  found  in  market.  The  juice  varies  from  year  to  year  accord- 
ing to  the  amount  of  rain,  sunshine,  average  temperature,  fertiliza- 
tion, and  other  causes ;  thus  the  proportion  of  sugar,  tannin,  acid, 
etc.,  changes,  and  the  wines  vary  somewhat  on  fermentation.  For 
this  reason,  must  or  new  wine  is  "  improved."  A  common  method 
is  to  mix  in  the  juice  of  other  kinds  of  grapes  or  to  add  new  wine  of 
different  character.  If  the  must  is  too  high  in  sugar  and  low  in 
acid,  a  sour  wine  is  added  until  the  desired  ratio  is  obtained.  If 
already  too  sour,  it  is  "  Gallized  "  by  adding  water  and  sugar,  or 
"  Chaptalized  "  by  neutralizing  the  excess  of  acid  with  marble  dust 
or  precipitated  calcium  carbonate.  To  make  a  sweet  wine,  a  con- 
siderable amount  of  cane  sugar  is  added. 

These  modifications  are  restricted  by  legal  enactment  in  most 
countries,  and  the  addition  of  large  quantities  of  alcohol,  glucose, 
and  glycerine  (Scheeleizing)  is  generally  prohibited.  But  in  the  case 
of  certain  heavy  Spanish  and  Portuguese  wines,  such  as  Port  and 
Madeira,  the  addition  of  rectified  alcohol  is  recognized  as  legitimate. 
But  such  substances  as  logwood,  cochineal,  kermes,  or  other  natural 
or  coal-tar  coloring  matters,  are  considered  adulterants. 

Much  inferior  wine  is  made  by  leaching  the  pulp  ("  marc  ")  from 
the  wine-press '  with  water,  adding  sugar,  and  fermenting  the  ex- 
tract. This  gives  a  cheap  wine,  much  used  by  the  poorer  people  of 
European  countries.  But  it  must  not  be  sold  as  a  natural  wine. 

Considerable  artificial  wine  is  made  by  mixing  water,  alcohol, 
sugar,  glycerine,  tartaric  acid,  tannin,  fruit  essences,  etc.,  to  produce 
a  liquor  resembling  the  natural  product.  Within  a  few  years  an 
industry  has  been  established  in  France  for  the  manufacture  of 
wine  from  raisins  and  prunes.  These  are  macerated  in  a  mixture 
of  water,  brandy,  sugar,  tartaric  and  tannic  acids,  and  the  whole 
fermented  with  yeast.  The  product  is  colored  if  desired. 

Champagne  is  made  from  certain  sweet  white  wines.  The  must 
is  pressed  from  the  grape  as  soon  as  possible  after  picking,  and  then 
fermented.  The  new  wine  is  clarified  with  isinglass  and  "  improved  " 
very  carefully  by  mixing  with  other  wines.  A  certain  amount  of 
cane  sugar  mixed  with  Cognac  is'  then  added  and  the  wine  bottled 


444  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

(the  best  corks,  which  have  been  soaked  in  wine,  are  used)  and  placed 
in  a  room  warmed  to  24°  C.  A  fermentation  takes  place  in  the  bottle 
and  the  wine  becomes  highly  charged  with  carbon  dioxide.  The 
amount  of  sugar  added  is  calculated  to  liberate  enough  of  this  gas 
to  cause  a  pressure  of  about  five  atmospheres  in  the  bottle.*  The 
bottles  are  placed  on  the  side  and  left  for  some  months;  then  they 
are  turned  with  the  cork  down,  until  the  sediment  collects  just 
above  it.  The  cork  is  then  carefully  removed  for  an  instant,  until 
the  sediment  has  blown  out.  The  loss  is  replaced  with  liqueur  (a 
solution  of  cane  sugar  and  aromatic  essences  in  the  best  Cognac), 
the  cork  is  replaced  and  wired  in,  and  the  liquor  is  ready  for  market. 
An  imitation  champagne  is  largely  made  by  forcing  carbon  dioxide 
into  a  sweet,  white  wine,  to  which  some  liqueur  has  been  added. 

Beside  grape  wines,  other  fermented  fruit  juices  are  used  as 
beverages.  Of  these,  the  commonest  in  this  country  are  hard  cider 
and  currant  wine.  These  do  not  keep  well  unless  sugar  has  been 
added  before  fermenting. 

Palm  wine  is  made  in  tropical  countries  from  the  sap  of  the  palm. 

Pulke  is  a  drink  prepared  in  Mexico  from  the  juice  of  certain 
cactus  plants. 

Kumiss  is  a  winelike  drink  made  from  the  fermented  milk  of 
cows,  mares,  or  goats.  The  milk  sugar  is  converted  into  lactic  acid, 
alcohol,  and  carbon  dioxide.  It  is  chiefly  made  by  the  inhabitants 
of  the  Russian  steppes. 

BREWING 

Brewing  involves  alcoholic  fermentation,  but  it  differs  from  wine 
making  in  that  it  is  always  started  by  the  addition  of  yeast  to  the 
liquid  to  be  fermented.  Spontaneous  fermentation  is  not  desired, 
and  precautions  are  taken  to  prevent  it. 

Beer  is  a  fermented  alcoholic  drink  intended  for  consumption 
during  the  after-fermentation,  while  still  charged  with  carbon  diox- 
ide. It  is  made  from  sprouted  grain  (malt),  starchy  materials, 
and  hops.  The  malt  is  generally  barley,  as  this  yields  the  largest 
percentage  of  diastase  and  affords  the  richest,  best  flavored  beer.f 
The  starchy  material  is  derived  from  unmalted  corn,  rice,  or  other 
grain. 

*  From  5  to  8  per  cent  of  the  bottles  burst. 

t  Wheat,  corn,  and  other  grains  are  occasionally  malted  for  certain  kinds  of 
beer. 


FERMENTATION   INDUSTRIES  445 

The  quality  of  the  water  used  for  brewing  is  important  as  affect- 
ing the  product.  In  general,  the  water  should  be  moderately  hard 
and  the  salts  desired  in  it  are  calcium  and  magnesium  sulphates  and 
sodium  chloride.  If  much  iron  is  present,  the  water  should  be  puri- 
fied ;  very  soft  water  is  improved  by  the  addition  of  gypsum.  Water 
containing  much  organic  matter  in  solution,  or  an  unduly  large  num- 
ber of  bacteria,  should  not  be  used. 

The  process  of  brewing  may  be  divided  into  malting,  mashing 
(including  the  boiling  and  cooling  of  the  wort),  fermentation,  and 
bottling  or  barrelling. 

Malting  is  now  generally  done  by  separate  concerns,  except 
in  only  the  largest  breweries.  The  process  consists  in  cleaning 
softening,  sprouting,  and  drying  the  grain.  During  the  sprouting, 
two  ferments,  diastase  and  peptase,  are  formed,  while  the  cell  walls 
enclosing  the  starch  are  softened  and  disintegrated  so  that  the  inte- 
rior of  the  kernel  becomes  "  mealy,"  thus  facilitating  the  transforma-' 
tion  of  the  starch  into  sugar.  The  production  of  diastase  is  the 
chief  aim  of  the  maltster.  The  secretion  of  this  ferment  increases 
as  the  germination  proceeds,  until  it  reaches  a  maximum,  after 
which  it  decreases  if  the  germination  is  not  stopped.  The  amount 
of  diastase  is  estimated  by  the  length  of  the  sprout  or  acrospire,  and 
is  greatest  when  this  has  extended  about  three-fourths  of  the  length 
of  the  grain.  The  appearance  and  length  of  the  rootlets  also  serve 
as  a  guide  to  the  experienced  maltster. 

The  mode  of  the  formation  of  the  diastase  is  not  yet  known. 
It  is  a  nitrogenous  body,  easily  soluble  in  cold  water  and  possess- 
ing the  power  to  convert  large  quantities  of  starch  into  maltose 
(CtfH^On),  and  dextrin.  Since  good  malt  contains  a  great  excess  of 
diastase  over  the  amount  needed  to  convert  its  own  starch  into 
sugar,  mixtures  of  raw  grain  and  malt  are  allowed  to  react  until  the 
starch  of  the  former  is  converted  into  sugar,  and  then  the  whole  is 
fermented. 

The  dust,  dirt,  dead  and  broken  kernels,  and  foreign  seeds  are 
first  removed  by  careful  sieving  in  revolving  sieves,  the  dust  and 
chaff  being  blown  away  by  a  strong  blast  of  air. 

The  grain  is  then  "  steeped  "  by  soaking  it  for  two  or  three  days 
in  water  at  12°  C.,  in  wood-lined  tanks  or  cemented  cisterns.  It  is 
stirred  frequently,  and  the  dead  kernels  float  and  are  removed.  The 
water  extracts  much  soluble  matter,  oil,  etc.,  from  the  grain,  and  is 
changed  as  it  becomes  colored. 

The  grain  increases  about  20  or  25  per  cent  in  volume  and  about 


446  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

50  per  cent  in  weight,  and  when  a  test  of  a  few  kernels  shows  that 
they  are  so  soft  that  the  skin  may  be  readily  removed,  the  grain  is 
couched  by  piling  in  a  nicely  levelled  heap  about  20  to  24  inches 
deep,  on  the  malting  floor,  which  is  made  of  cement  and  is  kept  very 
clean.  The  room  is  usually  only  moderately  lighted,  and  the  air 
is  kept  moist  by  frequently  sprinkling  the  grain  and  floor  with  water ; 
a  good  circulation  of  air  in  the  room  to  supply  plenty  of  oxygen  to 
the  grain  is  a  prime  essential.  Great  care  is  taken  to  keep  the  tem- 
perature even,  at  about  15°  to  16°  C.  Higher  temperature  tends  to 
cause  mould  growth  and  excessive  root  development.  After  a  few 
hours  the  temperature  begins  to  rise  within  the  couch,  and,  as  the 
grain  heats,  it  becomes  moist  on  the  surface  ("  sweats  ")  and  evolves 
an  agreeable  odor.  The  germination  has  begun,  and  soon  the  root- 
lets appear.  The  time  of  couching  is  from  20  to  30  hours,  according 
to  the  temperature  and  time  of  steeping. 

The  grain  is  then  floored  by  spreading  it  with  wooden  shovels  on 
the  floor,  in  an  even  layer  about  10  inches  deep.  To  prevent  its 
heating  too  rapidly,  it  is  turned  over  every  5  or  6  hours,  thus  bring- 
ing new  grain  to  the  top ;  each  succeeding  day  the  layer  is  spread 
thinner,  until  it  is  finally  only  4  inches  deep ;  the  grain  is  sprinkled 
from  time  to  time  to  keep  it  moist.  The  germination  is  rapid  and 
must  be  carefully  watched ;  after  from  6  to  12  days,  when  the  aero- 
spire  has  reached  the  desired  length,  the  growth  is  stopped  by  spread- 
ing it  in  thinner  layers  ;  the  moisture  evaporates  and  the  germ  withers. 
The  "  green  malt  "  is  then  transferred  to  the  drying  room,  which 
usually  has  two  floors,  made  of  wire  gauze  or  perforated  iron  plates. 
The  malt  is  spread  on  the  upper  floor  and  dried  at  a  temperature  of 
38°  to  50°  C.  To  produce  kiln-dried  malt,  it  is  transferred  to  the 
lower  floor,  where  it  is  much  hotter,  and  is  dried  at  100°  C. ;  some- 
times it  is  even  partially  charred.  The  air  in  the  drying  room  may 
be  heated  by  fire  gases  passing  through  pipes  under  the  gratings,  or 
by  an  open  fire  in  the  lower  part  of  the  room ;  in  this  latter  case  the 
products  of  combustion  pass  through  the  malt,  imparting  a  darker 
color  and  a  peculiar  taste  to  it  and  to  the  beer  made  from  it.  The 
character  and  color  of  the  beer  are  much  influenced  by  the  mode  of 
drying  the  malt.  The  higher  the  temperature,  the  more  diastase 
is  destroyed  and  the  less  soluble  the  protein  is  rendered.  After 
drying,  the  rootlets  are  brittle  and  are  easily  removed  by  passing  the 
malt  through  cylindrical  sieves  containing  rotary  brushes. 

The  production  of  a  malt  uniform  in  its  properties  throughout  by 
the  above  method  is  difficult,  while  different  lots  are  sure  to  vary 


FERMENTATION    INDUSTRIES 


447 


a  good  deal,  according  to  the  temperature  and  humidity  of  the  air. 
Consequently,  at  certain  seasons  of  the  year,  it  was  customary  to 
suspend  operations.  Pneumatic  malting,  as  it  remedies  the  above 
difficulties,  prevents  mould  and  acidity,  is  easily  controlled,  and  re- 
quires less  labor  and  less  floor  space,  has  replaced  the  old  system  in 
all  large  malt  houses.  Two  forms  of  pneumatic  malting  have  been 
devised. 

The  Galland  process  consists  in  placing  the  softened  grain  in  a 
rotating  drum  (Fig.  118),  containing  along  its  inner  circumference 
several  channels  (A,  A),  covered  with  wire  gauze  and  opening  into 
the  chamber  (C)  at  the  end  of  the  drum.  A  tube  (B)  of  wire  gauze 


FIG.  118. 


extends  along  the  centre  of  the  drum  and  connects  with  an  outlet 
pipe  (E).  Into  the  chamber  (C)  a  pipe  (D)  opens,  which  contains  a 
valve  that  makes  connection  with  the  flue  (F),  or  with  the  pipe  (G), 
as  desired.  Air  is  drawn  through  coke  towers,  kept  at  a  constant 
temperature  of  about  14°  C.,  and  through  which  water  trickles.  The 
air  then  passes  down  the  flue  (H),  where  it  is  in  contact  with  a  fine 
spray  of  water  escaping  under  pressure  from  the  supply  pipe  (J).  It 
is  thus  cooled,  or  warmed,  as  necessary  to  the  constant  temperature 
of  14°  C.,  and,  laden  with  moisture,  passes  through  (F)  and  (D)  into 
the  chamber  (C),  and  thence  into  the  drum,  through  the  channels 
(A,  A).  The  drum  is  filled  about  two-thirds  full  with  the  swollen 
grain ;  and  as  it  rotates  about  once  in  40  to  50  minutes,  there  is  a 


448  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

slow  turning  over  of  the  whole  mass  of  the  grain.  The  air,  entering 
through  (A,  A),  passes  through  the  mass,  and  enters  the  inner  tube 
(B),  from  which  it  passes  to  (E),  and  thence  to  the  exhauster,  which 
drives  it  out  of  the  building.  Thus  the  grain  is  kept  at  a  constant 
temperature  in  a  moist  atmosphere,  with  effective  circulation  of  air, 
and  a  constant  change  of  surface  of  the  kernels,  which  prevents  un- 
due heating.  The  grain  sprouts  as  on  the  malting  floor,  but  there  is 
no  handling  and  consequent  breaking  and  crushing  of  the  kernel, 
and  no  opportunity  for  the  development  of  mould;  since  the  air 
is  filtered,  very  few  germs  are  introduced.  When  the  germination 
has  gone  as  far  as  is  desired,  the  valve  in  (D)  is  changed  to  cut  off 
the  moist  air,  and  connection  is  made  with  (G),  from  which  warm, 
dry  air  is  drawn  into  the  drum,  rapidly  drying  the  acrospire  and 
rootlets.  The  drums  hold  from  lj  to  5  tons  of  barley  at  a  charge, 
and  the  time  necessary  for  the  process  is  about  8  days. 

By  the  Saladin  system,  the  softened  barley  is  placed  in  a  long 
tank,  having  a  false  bottom  of  gauze,  and  provided  with  a  mechan- 
ical stirring  apparatus,  travelling  from  one  end  of  the  tank  to  the 
other  on  a  movable  carriage.  This  stirrer  hangs  down  into  the 
grain,  and  mixes  it  effectively  without  crushing  any  kernels.  Moist 
air  enters  under  the  false  bottom,  and  passing  through  the  wet  grain, 
escapes  into  the  room,  and  is  drawn  away  by  an  exhauster.  When 
the  sprouting  is  ended,  warm,  dry  air  is  drawn  through  the  malt,  as 
above  described. 

Mashing  consists  in  converting  the  starch  in  the  mixture  of  grain 
and  malt  into  maltose  and  dextrin,  through  the  action  of  the  dias- 
tase in  the  malt,  and  at  the  same  time  extracting  the  soluble  carbo- 
hydrates and  nitrogenous  bodies.  The  peptase,  going  into  solution, 
is  supposed  to  convert  part  of  the  albuminoids  into  peptones  and 
amides,  which  are  readily  soluble  in  water,  and  constitute  a  part  of 
the  "  extract  "  present  in  the  finished  beer.  Some  of  these  bodies, 
however,  if  present  in  a  large  amount,  may  cause  cloudiness  in  the 
product,  as  they  are  precipitated  from  cold  solution  by  alcohol.  It 
is  generally  supposed  that  by  drying  the  malt  at  a  high  temperature 
these  protein  substances  are  rendered  less  soluble  in  the  mash  liquor, 
and  being  thus  filtered  out,  the  beer  is  clear  and  bright.  The  use 
of  unmalted  grain,  especially  corn  or  rice,  in  mashing,  is  also  advo- 
cated,* on  the  ground  that  it  contains  no  protein  matter  to  cloud  the 

*  Robert  Wahl,  Indian  Corn  in  the  Manufacture  of  Beer,  U.  S.  Dep't  Agricul- 
ture, Washington,  1893. 


FERMENTATION   INDUSTRIES  449 

beer.  But  the  real  nature  and  value  of  peptones  in  the  mash  liquor 
is  not  yet  definitely  settled. 

The  most  favorable  temperature  for  the  action  of  the  diastase  is 
from  60°  to  65°  C.,  at  which  point  it  rapidly  hydrolyzes  the  starch, 
and  converts  it  into  maltose  and  numerous  dextrins,  —  amylodex- 
trin,  erythrodextrin,  and  archodextrin  probably  being  intermediate 
products.  About  one-fourth  of  the  starch  is  usually  left  in  the  form 
of  dextrin. 

According  to  Ost,  the  large  starch  molecule  decomposes  into  sev- 
eral smaller  dextrin  molecules  :  — 

mn(Ci2H2oOio)  =  n(mCi2H2oOio). 

Of  these  dextrins,  some  combine  with  water  to  form  maltodextrin, 
an  intermediate  product  between  dextrin  and  maltose,  which  fer- 
ments very  quickly  with  top  yeast.  These  dextrins  are  further 
converted  into  maltose  by  the  diastase  :  — 

mH2O  =  m(Ci2H22On). 


A  complete  conversion  of  the  starch  into  maltose  is  not  desired 
for  beer,  since  the  presence  of  the  unfermentable  dextrin  imparts 
fulness  of  body  and  nutritive  properties,  which  are  increased  by  the 
albuminoids,  peptones,  and  amides.  These  also  keep  up  a  slow  fer- 
mentation after  the  beer  has  been  drawn  into  casks  or  bottles.  It  is 
often  customary,  therefore,  to  limit  the  diastatic  action  by  kiln-dry- 
ing the  malt  at  a  high  temperature,  or  by  mashing  with  very  hot 
water  at  first,  or  by  rapidly  heating  a  part  of  the  mash  to  boiling. 

There  are  two  general  processes  of  mashing  :  the  infusion  method, 
generally  practised  in  the  United  States  and  in  England;  and  the 
decoction  method,  usually  employed  in  Europe.  By  the  former  pro- 
cess the  dry  malt  is  crushed  between  rolls  so  that  the  hull  bursts,  but 
it  is  not  ground.  It  then  passes  into  a  large  "  mash-tub,"  provided 
with  a  cover  and  an  effective  stirring  apparatus.  English  brewers 
mix  the  malt  directly  with  hot  water  at  75°  C.,  as  it  saves  time  and 
labor,  and  the  extraction  of  the  malt  seems  to  be  more  complete. 
But  this  hot  water  destroys  much  of  the  diastase,  and  prevents  the 
complete  action  of  the  peptase  on  the  albuminoids,  thus  leaving 
them  in  the  beer,  where  they  sometimes  cause  cloudiness. 

American  brewers  usually  mix  the  malt  with  a  little  water  at 
50°  to  60°  C.,  and  the  temperature  is  kept  there  for  some  time,  as 
this  is  the  most  favorable  temperature  for  the  diastase  and  peptones 
to  do  their  work.  Then  the  mash  is  slowly  heated  to  70°  C.,  by 


450  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

running  in  boiling  water  or  free  steam.  By  this  slow  heating  the 
starch  is  all  converted  by  the  diastase  before  it  is  hot  enough  to 
form  a  paste.  Some  brewers  prefer  to  start  with  cold  water  in  the 
mash-tub,  and  heat  slowly  to  70°. 

The  raw  cereal  used  in  the  mash  is  generally  ground  and  mixed 
with  a  small  quantity  of  the  malt  in  a  special  tub ;  then  water  at 
about  38°  C.  is  run  in,  and  after  about  30  minutes  the  temperature  is 
raised  to  60°  C.,  where  it  remains  another  half -hour,  the  stirrer 
being  in  constant  operation.  Then  the  mixture  is  heated  to  boiling 
for  an  hour,  and  finally  the  softened  raw  grain  is  run  into  the  mash- 
tub,  where  the  rest  of  the  malt  has  been  wet  with  water  at  38°  C., 
and  the  mashing  process  proceeds  as  above. 

Mashing  usually  takes  an  hour  or  more,  and  the  stirrer  is  kept  in 
constant  operation.  The  product  is  a  liquid  called  "  wort,"  contain- 
ing maltose,  isomaltose,  dextrins,  peptones,  and  amides. 

The  decoction  process  yields  a  more  concentrated  wort,  and  is 
generally  used  where  fuel  is  expensive,  and  when  a  full-bodied,  highly 
extractive  beer  is  desired.  The  crushed  malt  is  mixed  with  twice 
its  volume  of  cold  water  in  the  mash-tub,  and  then  the  full  amount  of 
water  desired  is  made  up  by  adding  boiling  water,  thus  raising  the 
temperature  of  the  mash  to  38°  C.  About  one-third  of  the 
whole  mash  is  then  pumped  into  the  decoction  pan  (a  boiler 
heated  either  by  free  fire  or  by  steam,  and  having  a  good  stirrer), 
where  it  is  rapidly  heated  to  boiling,  and  at  once  run  back  into  the 
mash-tub,  where  the  stirrer  is  working  actively.  This  raises  the 
temperature  of  the  mash  to  about  50°  C.  Again  one-third  of  the 
contents  of  the  mash-tub  is  heated  to  boiling  in  the  decoction  pan, 
and  run  back,  heating  the  mash  to  62°  C.  Another  repetition  of 
this  process  raises  the  temperature  to  70°  to  72°  C.,  when  the  mash 
is  allowed  to  stand  quietly  for  30  minutes. 

The  wort  obtained  by  either  process  is  filtered'  from  the  husks  of 
the  malt  and  other  solid  residue.  When  the  infusion  process  is 
used,  the  mash-tub  generally  has  a  false  bottom  of  perforated  copper 
plate,  the  holes  being  sufficiently  fine  to  retain  the  residue.  When 
the  stirrer  is  stopped,  this  insoluble  matter  settles  to  the  bottom, 
and  collecting  on  the  grating,  forms  a  filtering  layer  which  retains 
the  suspended  matter,  while  the  wort  is  drawn  off  below  the  false 
bottom.  The  first  runnings  are  turbid,  and  are  refiltered.  In  the 
.decoction  process,  it  is  customary  to  run  the  mash  into  a  special  tub 
for  this  filtration.  In  order  to  remove  all  the  wort  from  the  residue, 
a  washer  called  a  "  sparger  "  is  used.  This  is  merely  a  large  Bar- 


FERMENTATION    INDUSTRIES  451 

ker's  mill  with  arms  extending  to  within  half  an  inch  of  the  sides 
of  the  mash-tub,  and  with  a  row  of  holes  one-twentieth  of  an  inch 
in  diameter,  and  two  inches  apart,  extending  along  the  back  of  each 
arm.  The  flow  of  water  causes  the  arms  to  rotate  and  it  is  evenly 
distributed.  The  process  is  continued  with  hot  water  (75°  C.) 
until  the  washings  reach  a  density  of  1°  Tw. 

The  filtered  wort  is  next  run  into  the  brewing  kettle  or  copper, 
where  it  is  boiled  for  some  time.  This  has  several  objects :  — 

(a)  It  concentrates  the  wort,  which,  by  the  infusion  process  espe- 
cially, is  very  dilute,  and  about  one-fourth  of  the  water  must  be  evap- 
orated. 

(6)  It  destroys  the  diastase,  peptase,  and  any  other  'ferment 
which  may  be  present,  and  thoroughly  sterilizes  the  wort. 

(c)  It  coagulates  and  precipitates  most  of  the  albuminous  matter 
remaining  in  the  wort. 

(d)  It   affords   an   opportunity   of  adding   the   hops,   which  are 
boiled  with  the  wort  from  one-half  an  hour  to  an  hour. 

Hops  are  the  female  flowers  (catkins)  of  Humulus  Lupulus,  L. 
The  leaflets  contain  tannin,  while  the  yellow  powder  (lupulin,  hop 
meal,  or  hop  flour),  attached  to  the  surface  of  the  catkin,  contains 
hop  oil,  certain  alkaloids  or  bitter  principles,  and  resins.  The  oil  is 
volatile,  and  is  present  to  the  extent  of  0.25  to  0.30  per  cent.  It 
imparts  the  bitter  flavor  to  the  beer.  If  boiled  too  long,  part  of  this 
oil  is  lost.  The  alkaloids  are  supposed  to  give  the  narcotic  char- 
acter to  hops.  The  resins  contain  most  of  the  antiseptic  principles, 
which  are  protective  against  the  lactic  ferment,  and,  to  a  less  degree, 
against  the  acetic  ferment ;  hence  more  hops  are  added  to  lager  beer 
which  is  stored  several  months  before  going  to  market,  than  to  that 
intended  for  immediate  consumption.  About  one  pound  of  hops  to  100 
gallons  of  wort  is  the  lowest  limit,  while  as  much  as  12  pounds  per 
100  gallons  are  used  for  some  of  the  heavy  English  ales  and  porters. 

The  best  varieties  of  hops  are  raised  in  Bohemia  and  Bavaria, 
but  they  are  also  largely  cultivated  in  other  parts  of  Germany,  in 
France,  and  in  the  United  States. 

,  After  boiling  the  wort  from  one  to  six  hours,  according  to  the 
character  of  the  wort,  and  of  the  beer  desired,  the  hop  catkins  are 
removed  by  straining  the  wort  through  sieves  in  a  vessel  called  the 
"hop-back."  They  are  then  washed,  and  sometimes  pressed,  to 
obtain  all  the  extractive  matter. 

The  hot  wort  is  then  pumped  through  a  rose  or  sprayer  into  a 
receiving  tank  placed  in  a  well-ventilated  room.  It  falls  for  some 


452  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

distance  as  a  fine  mist,  and  is  aerated  and  cooled  some  25°  to  30°. 
It  stands  in  this  tank  until  a  sediment  deposits.  The  wort  is  still 
hot,  and  is  drawn  off  and  rapidly  cooled*  to  the  temperature  of 
fermentation  by  running  over  the  Baudelot  cooler,  or  "  beer-fall."  f 
This  consists  of  a  series  of  horizontal  copper  pipes,  about  two  and 
one-half  inches  in  diameter,  placed,  one  above  the  other,  to  a  height 
of  ten  or  twelve  feet,  and  through  which  cold  water  or  ammonia 
circulates ;  the  wort,  running  over  the  surface  of  the  pipes  in  thin 
films,  is  quickly  cooled  to  the  temperature  of  the  water.  Sometimes 
the  flow  of  wort  is  inside  the  pipes,  and  the  water  passes  over  the 
outside  of  the  beer-fall. 

From  the  cooler,  the  wort  passes  to  a  tank,  where  it  is  allowed  to 
settle,  and  the  clear  liquid  is  then  drawn  into  the  fermentation  butts. 
These  are  made  of  oak,  and  lined  with  pitch  or  asphaltum,  and 
hold  from  1500  to  3000  gallons.  They  are  set  in  underground  cel- 
lars or,  more  commonly  now,  in  rooms  cooled  to  a  constant  tem- 
perature by  refrigerating  machines;  or  water,  cooled  to  the  tem- 
perature of  fermentation,  flows  through  a  coil  of  copper  pipe  placed 
in  the  butt.  A  certain  amount  of  pure  yeast  is  added  to  each  tub, 
the  process  being  called  "  pitching,"  and  within  a  few  hours  the 
active  fernlentation  begins.  In  some  breweries  it  is  the  practice  to 
add  the  yeast  in  the  settling  tanks ;  after  a  few  hours  the  wort  is 
drawn  from  above  the  sediment  (consisting  of  coagulated  albuminous 
matter,  dead  yeast  cells,  hops,  and  other  solid  impurities),  and  passes 
into  the  fermentation  butts,  carrying  with  it  enough  young  yeast  cells 
to  cause  active  fermentation.  According  as  the  temperature  of  the 
wort  is  low  (5°  to  8°  C.)  or  high  (15°  to  18°  C.)  there  is  a  "  bottom  "  or 
a  "  top  fermentation."  The  former  is  used  for  lager  beers,  and  the 
latter  for  ale,  porter,  and  stout. 

In  the  bottom  fermentation  the  active  fermentation  does  not 
begin  for  12  to  18  hours  after  pitching.  Then  a  scum  appears  on 
the  wort,  and  is  blown  into  a  foam  by  the  escaping  carbon  dioxide. 
After  three  or  four  days  this  foam  rises  to  the  top,  or  even  several 
inches  above  the  top  of  the  butt,  while  its  surface  is  broken  by  deep 
cracks.  The  carbon  dioxide  escapes  over- the  sides  of  the  butt,  and 

*  Lactic  or  acetic  fermentation,  which  would  sour  the  beer,  is  apt  to  take  place 
during  the  cooling.  To  prevent  infection  of  the  wort  by  bacteria  and  wild  yeasts, 
systems  for  ventilating  the  cooling  rooms  with  filtered  or  sterilized  air  are  often 
used. 

t  This  apparatus  has  generally  replaced  the  old-style,  shallow  cooling  pans  in 
which  the  wort  was  exposed  to  the  air  in  a  broad  layer  only  a  few  inches  deep. 


FERMENTATION   INDUSTRIES  453 

falling  to  the  floor  is -usually  carried  away  by  an  artificial  draught.* 
Finally  the  surface  of  the  foam  shows  a  brown  color,  and  in  six  or 
seven  days  the  active  fermentation  diminishes,  the  temperature  falls, 
and  the  yeast  settles  to  the  bottom.  After  ten  days  the  active 
fermentation  ceases  entirely,  and  the  new  beer  is  drawn  into  storage 
vats,  carrying  with  it  some  yeast,  which  sets  up  an  after-fermenta- 
tion; the  maltose  remaining  is  slowly  decomposed,  and  substances 
are  formed  which  improve  the  flavor.  These  casks  are  of  oak,  coated 
with  pitch  inside,  and  usually  holding  about  1500  gallons.  The 
temperature  during  this  period  is  kept  low,  and  air  is  given  free 
access  to  the  liquor.  The  yeast  grows  thriftily,  and  consumes  more 
of  the  albumins,  so  that  lager  beers  are  lower  in  these,  and  are  more 
stable  than  top-fermentation  beers.  The  time  of  this  storage  varies 
from  three  to  six  months.  To  assist  in  clarifying  it,  the  beer  is 
usually  drawn  into  "  chip  casks,"  in  which  are  vshavings  of  beech 
wood  which  have  been  well  cleaned  by  boiling  with  sodium  carbon- 
ate. For  the  game  purpose,  isinglass  dissolved  in  tartaric  or  sul- 
phurous acid  is  usually  added  in  the  chip  casks,  together  with  some 
actively  fermenting  young  beer.  The  yeast  cells  attach  themselves 
to  the  shavings,  and  the  beer  is  left  clear. 

Top  fermentation  is  usually  employed  in  England,  and  largely  in 
this  country  for  ales,  etc.  The  fermentation  is  very  active,  usually 
ending  in  from  three  to  five  days,  and  the  yeast  is  partly  carried  to 
the  surface  of  the  wort  by  the  rapid  evolution  of  the  carbon  dioxide. 
A  certain  amount  of  bottom  yeast  is  also  formed.  The  top  yeast  is 
removed  by  skimming,  and  the  beer  is  drawn  into  small  casks,  hold- 
ing from  two  to  four  barrels  each  for  the  after-fermentation.  These 

*  The  amount  of  carbon  dioxide  formed  is  said  to  be  about  equal  to  the  weight 
of  the  alcohol.  Methods  have  recently  been  devised  to  save  this  gas  for  use  in 
refrigerating  machines,  or  for  carbonating  the  finished  beer.  It  is  evolved  rapidly 
and  regularly  for  some  time,  and  is  collected  in  a  hood  let  down  over  the  fermenta- 
tion vat  to  within  a  few  inches  of  the  surface  of  the  liquid.  The  level  of  the  gas  is 
gauged  by  means  of  a  toy  rubber  balloon,  filled  with  air,  which  floats  on  the  surface 
of  the  gas.  The  carbon  dioxide  is  carefully  pumped  from  the  hood  so  that  no  air  is 
drawn  with  it.  It  is  then  purified  by  passing  through  water,  and  then  through  a 
solution  of  potassium  permanganate,  and  finally  through  concentrated  sulphuric 
acid.  It  is  compressed  at  about  60  atmospheres,  and  then  passed  through  cooling 
coils  for  condensation.  The  compressed  gas  is  said  to  be  about  99  per  cent  pure,  and 
is  used  to  some  extent  to  force  the  beer  through  the  various  pipes  from  the  storage 
cellar  to  the  place  where  it  is  drawn  into  casks  or  bottles,  thus  replacing  pumps  with 
their  contaminations.  It  is  also  used  in  the  cooling  machines,  being  circulated 
through  the  coils  instead  of  brine  or  water.  It  is  very  satisfactory  for  this  purpose, 
since  the  escaping  gas,  does  no  harm  in  case  there  is  a  leak.  About  2200  pounds  of 
liquid  carbon  dioxide  are  said  to  be  obtained  from  600  barrels  of  wort.  A.  Marcet, 
J.  Soc.  Chem.  Ind.,  1894,  825. 


454  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

casks  are  placed  in  a  cold  room,  and  the  process  goes  on  until  most 
of  the  yeast  has  been  forced  out  of  the  bung-hole.  The  cask  is  then 
bunged  and  allowed  to  stand  until  the  sediment  has  deposited,  when 
the  clear  beer  is  drawn  off  into  barrels  for  market.  Isinglass  or 
gelatine  is  often  added  to  assist  in  settling  the  sediment. 

Top  fermentation  is  favorable  to  the  development  of  other  fer- 
ments, and  a  high  percentage  of  alcohol  is  often  depended  upon  to 
prevent  these  growths.  In  order  to  increase  the  alcohol  and  dextrin 
without  increasing  the  quantity  of  malt,  it  is  frequently  customary 
to  add  sugar  or  glucose  to  the  wort  in  the  brewing  kettle. 

During  the  fermentation  the  contents  of  the  tub  are  stirred  occa- 
sionally to  aerate  the  wort.  The  progress  of  the  fermentation  is 
judged  by  the  readings  of  a  hydrometer,  and  as  the  density  of  the 
wort  decreases  as  the  fermentation  advances,  the  process  is  called 
"  attenuation."  The  temperature  is  carefully  watched,  and  not 
allowed  to  rise  above  18°  C. 

In  fermentation  by  the  "  vacuum  process,"  *  the  wort  is  fermented 
in  closed,  enamelled  iron  vessels,  from  which  the  carbon  dioxide  is 
pumped  away  as  liberated.  Thus  the  time  of  fermentation  and 
storage  is  reduced,  and  wild  yeasts  and  bacteria  are  excluded.  The 
gases  pumped  away  are  led  through  cooling  pipes  to  condense  some 
of  the  aromatic  flavoring  matters,  which  are  returned  to  the  beer 
after  the  fermentation  is  completed.  The  beer  is  finally  recharged 
with  CC>2  under  pressure,  just  before  bottling  or  barrelling. 

Besides  alcohol  and  carbon  dioxide,  beer  contains  glycerine,  suc- 
cinic  acid,  amides,  peptones,  and  dextrins.  Phosphoric,  acetic,  and 
lactic  acids  are  also  present  in  a  small  quantity.  All  the  soluble 
constituents  of  the  beer,  except  the  alcohol  and  carbon  dioxide,  and 
which  give  it  its  nutritive  qualities,  are  grouped  together  under  the 
name  of  "  extract."  English  ales,  porters,  and  stouts  are  rich  in 
extract,  but  most  German  and  American  beers  contain  only  a  moder- 
ate amount  of  it. 

Sometimes  beer  is  flavored  with  bitter  substances,  such  as  quas- 
sia and  gentian  root ;  or  ginger  or  coriander  may  be  added  for  pun- 
gency, but  this  is  prohibited  in  many  countries. 

Bottling  or  Barrelling.  —  Much  of  the  success  with  which  certain 
beers  meet  in  commerce  is  due  to  the  care  exercised  on  this  point. 
The  barrels  are  coated  on  the  inside  with  brewer's  pitch,  a  mixture 
of  rosin  and  rosin  oil  which  softens  at  50°  to  60°  C.  This  prevents 
the  beer  from  soaking  into  the  staves  and  extracting  color  or  flavor 
*  J.  Soc.  Chem.  Ind.,  1898,  1064. 


FERMENTATION   INDUSTRIES  455 

from  the  wood.  All  -barrels,  and  especially  old  ones  which  are  re- 
turned for  refilling,  should  be  thoroughly  scalded  and  washed  out. 
If  this  is  not  done,  the  beer  is  liable  to  sour  before  it  reaches  the  con- 
sumer. It  is  frequently  customary  to  fume  the  barrels  with  sulphur 
dioxide  or  to  wash  them  with  sulphurous  acid  or  bisulphite  of  cal- 
cium solution.  Fluoride  of  sodium  is  sometimes  used  to  wash  the 
yeast  and  in  cleaning  the  fermentation  tubs.  This  prevents  the  devel- 
opment of  injurious  ferments.  Salicylic  acid  is  often  added  to  improve 
the  keeping  qualities,  but  with  doubtful  benefit  to  the  consumer. 

Bottles  must  be  clean  and  only  the  best  quality  of  corks  should  be 
used.  Bottled  beer  is  usually  "  Pasteurized  "  at  60°  C.  for  about  an 
hour.  It  is  essential  that  both  barrels  and  bottles  should  be  entirely 
full,  for  if  an  air  space  is  left,  the  beer  becomes  flat  and  stale. 

The  quality  of  beer  depends  mainly  on  the  purity  of  the  water 
and  yeast  employed,  and  upon  the  care  taken  to  keep  all  parts  of 
the  brewery  exceedingly  clean.  All  vats,  tubs,  coolers,  and  pans 
must  be  thoroughly  washed  and  scalded  immediately  after  use,  and 
the  floors  and  walls  of  the  brewery  must  be  perfectly  clean. 

Various  kinds  of  beers  are  recognized  in  commerce,  according  to 
the  appearance,  mode  of  preparation,  flavor,  strength  of  alcohol  and 
of  extract,  etc. 

Ale  is  a  light-colored  beer,  often  rather  strong  in  alcohol,  and 
made  by  top  fermentation  with  the  use  of  a  large  amount  of  hops. 

Porter  is  a  dark-colored  beer,  containing  much  sugary  matter  and 
extract.  For  this,  the  malt  is  kiln  dried  at  such  a  high  temperature 
that  it  is  partially  charred,  forming  caramel,  which  colors  and  flavors 
the  beer. 

Stout  is  similar  to  porter,  but  contains  more  alcohol  and  extract. 

Lager  beer  is  made  by  bottom  fermentation,  is  rather  low  in 
alcohol,  and  contains  a  moderate  amount  of  extract.  Export  lagers 
are  made  from  stronger  worts  and  contain  more  alcohol  and  extract. 
A  special  brew  made  in  the  spring  from  very  concentrated  wort  and 
but  little  hops  is  called  bock  beer  or  Salvator  beer.  It  contains 
much  unfermented  sugar  and  will  not  keep  long. 

Berlin  weiss-bier  is  made  from  a  mixture  of  two  parts  malted 
wheat  to  one  of  barley  malt.  It  is  fermented  by  top  fermentation, 
and  is  usually  bottled  before  the  after-fermentation  is  ended.  Thus 
it  contains  much  carbon  dioxide  and  foams  excessively.  It  is  very 
light-colored  and  contains  lactic  acid. 

The  following  table  shows  the  average  composition  of  beers  ac- 
cording to  various  authors:, — 


456 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


SP.  GB. 

(17.50°  C.) 

ALCOHOL 

EXTRACT 

ACIDS 
(Acetic,  Lactic,  etc.) 

ASH 

Vienna  lager*    .... 

1.017 

3.70 

5.71 

0.008 

__ 

Pilsner  lager*    .... 

1.016 

3.43 

5.45 

0.008 

— 

Munich  export*      .     .     . 

1.020 

3.94 

6.72 

0.010 

— 

Munich  Salvator*  .     .     . 

— 

4.78 

10.67 

— 

— 

Berlin  weiss-bier*  .     .     . 

1.012 

2.82 

4.21 

— 

— 

Burton  pale  alef     • 

— 

5.37 

5.13 

0.16 

0.55 

Dublin  stout  XXX  f  .     . 

— 

6.78 

9.52 

0.29 

1.40 

Milwaukee  lager  J  . 

1.010 

4.28 

4.18 

0.057 

0.196 

Milwaukee  Bavarian  t 

1.0187 

5.06 

6.26 

0.074 

0.346 

St.  Louis  export!   . 

1.0178 

4.40 

6.15 

0.067 

0.312 

Philadelphia  lager  t     .     . 

1.0147 

4.29 

5.22 

0.086 

0.241 

DISTILLED  LIQUORS 

Distilled  liquors  are  obtained  by  distilling  alcoholic  liquids  pre- 
pared by  fermentation.  They  are  essentially  mixtures  of  ethyl 
alcohol  and  water  in  varying  proportions  with  minute  quantities  of 
organic  ethers  and  higher  alcohols.  Pure  ethyl  alcohol  may  be  con- 
sidered the  representative  and  chief  constituent  of  these  liquors. 
When  first  distilled,  they  contain  neither  extractive  nor  mineral 
matter,  and  are  much  stronger  in  alcojrol  than  fermented  liquors. 

Alcohol  is  always  prepared  on  a  technical  scale  by  fermenting 
sugar,  which  in  most  cases  is  derived  from  starch  by  conversion  with 
diastase,  or  from  the  molasses  of  the  sugar  industry.  In  the  United 
States  the  materials  employed  are  corn,  rye,  and  barley ;  in  England, 
barley,  rice,  corn,  and  rye  are  used ;  while  in  Germany,  the  potato 
and  molasses  are  the  principal  sources.  The  products  obtained  from 
these  several  raw  materials  vary  somewhat  in  their  character,  flavor, 
and  strength. 

Since  the  largest  possible  yield  of  alcohol  is  desired  from  a  given 
amount  of  starchy  material,  the  latter  is  so  treated  that  the  most 
complete  conversion  into  maltose  is  obtained  with  as  little  dextrin 
as  may  be.  This  is  accomplished  by  treating  the  starchy  material 
with  malt  prepared  with  the  view  of  obtaining  all  the  diastase  pos- 
sible. For  this  purpose,  the  germination  is  stopped  earlier  and  the 
drying  temperature  kept  lower  than  in  the  case  of  malt  for  brewing. 
The  preparation  of  pure  alcohol  from  corn  is  carried  on  about  as 

*  Ost,  Technischen  Chemie,  2te  Auf.,  p.  455. 

t  Allen,  Commercial  Organic  Analysis,  Vol.  II,  2d  ed.,  p.  92. 

$  Crampton,  U.  S.  Dep't  Agriculture,  Bulletin  No.  13,  part  3,  p.  282. 


FERMENTATION   INDUSTRIES  457 

follows :  The  corn,  usually  degerminated,  is  ground  to  a  coarse  meal, 
and  a  weighed  amount  of  this  meal  is  run  into  a  closed  iron  digester 
(called  a  "  cooker  ")  provided  with  a  stirring  apparatus.  Here  it  is 
mixed  with  water  and  heated  by  steam  under  two  or  three  atmos- 
pheres' pressure  for  an  hour  or  so.  It  is  then  blown  out  into  another 
vessel ;  or  it  may  be  cooled  in  the  cooker.  (The  cooling  is  sometimes 
hastened  by  exhausting  the  vapor  from  the  vessel  by  a  pump.)  When 
the  temperature  reaches  63°  C.,  the  required  amount  of  ground  malt, 
mixed  with  a  little  water,  is  added  and  the  mass  well  stirred.  The 
temperature  should  not  be  above  63°  C.,  in  order  that  the  least 
possible  amount  of  dextrin  may  be  formed.  The  resulting  wort  is 
drawn  off  through  a  sieve  to  remove  the  grain  husks,  which  are  washed 
with  hot  water  and  the  washings  added  to  the  wort.  This  is  then 
rapidly  cooled  (to  prevent  the  development  of  acetic  fermentation) 
and  drawn  into  the  fermenting  vats.  These  are  large  cylindrical 
wooden  tubs  (sometimes  25  feet  deep  by  20  feet  in  diameter),  one 
being  emptied  and  another  recharged  every  day.  The  fermentation 
of  the  wort  is  started  by  adding  yeast,  as  in  brewing ;  but  for  alcohol, 
the  quantity  of  yeast  and  the  temperature  of  fermentation  are  regu- 
lated with  a  view  to  converting  all  of  the  sugar  into  alcohol  as  rapidly* 
and  completely  as  possible.  Too  slow  fermentation  favors  the  devel- 
opment of  the  acetic  and  lactic  fermentations,  with  resulting  loss  of 
alcohol.  The  temperature  is  high,  being  20°  to  25°  C.,  and  an  active 
top  fermentation  is  carried  on.  If  the  temperature  rises  much  above 
25°  C.,  some  loss  of  alcohol  by  evaporation  occurs.  During  the  final 
part  of  the  fermentation,  some  of  the  dextrin  in  the  wort  is  converted 
into  maltose  by  diastase  still  remaining,  and  this  sugar  is  also  fer- 
mented by  the  yeast. 

To  prevent  the  development  of  bacteria  and  wild  yeasts,  a  little 
hydrofluoric  acid,  or  alkali  fluoride,  is  often  added  to  the  mash,  after 
the  conversion  of  the  starch  by  the  diastase.  It  increases  the  yield 
of  alcohol  by  preventing  secondary  fermentations,  and  tends  to  reduce 
frothing.  It  is  also  used  as  a  disinfectant  and  germicide  for  general 
cleaning  of  the  tubs  and  vats. 

When  the  fermentation  ceases,  the  mash  consists  of  a  mixture 

*  The  legal  limits  of  time  within  which  fermentations  must  be  completed  are : 
For  sweet-mash  distilleries  (where  specially  prepared  yeast  is  added  directly  to  the 
wort) ,  72  hours ;  for  sour-mash  distilleries  (in  which  the  fermenting  agents  used 
are  the  spent  beer,  or  slop,  and  barm  from  a  tub  previously  fermented),  96  hours ; 
and  for  rum  distilleries,  144  hours.  At  the  end  of  these  periods  the  fermenting  tub 
must  be  emptied  ;  it  may  be  emptied  in  less  time,  but  cannot  be  refilled  until 
the  full  time  limit  has  expired. 


458  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

of  slimy,  solid  matter,  with  water,  alcohol,  fusel  oil,  acids,  etc.  The 
amount  of  alcohol  varies  from  10  to  13  per  cent  by  volume,  and  is 
separated  from  the  other  constituents  by  distillation.  This  was 
formerly  carried  on  in  simple  stills,*  heated  by  direct  firing,  and 
connected  with  a  condensing  worm.  They  were  intermittent  in 
action  and  yielded  a  very  dilute  distillate,  which  had  to  be  repeat- 
edly redistilled  to  obtain  a  strong  alcohol;  thus,  e.g.  from  a  mash 
containing  10  per  cent  alcohol,  the  first  distillate  contains  about 
28  per  cent  alcohol;  by  redistilling  this  distillate,  the  alcohol  per- 
centage is  raised  to  50  per  cent ;  by  another  redistillation  it  is  raised 
to  70  per  cent,  and  this  in  turn  yields  an  80  per  cent  alcohol.  By 
many  redistillations,  an  alcohol  of  95  per  cent  may  be  obtained,  but 
above  this  redistillation  yields  no  further  separation. 

But  the  principle  of  fractional  condensation  is  now  employed, 
and  improved  stills,  with  dephlegmation  and  rectifying  apparatus, 
make  it  possible  to  obtain  concentrated  alcohol  by  two  distillations. 
The  old  interrupted  working  has  given  way  to  continuous  processes, 
by  which  the  inflow  of  mash  and  the  outflow  of  spent  mash  (slops)  are 
unbroken. 

For  distilling  potato  mashes,  which  are  thick  and  slimy,  no  con- 
tinuous-acting still  has  proved  successful,  and  the  intermittent  Pis- 
torius  apparatus,  consisting  of  two  connected  stills  and  a  dephleg- 
mator,  is  much  used.  The  Coffey  still  (p.  12)  in  various  modified 
forms  is  largely  used  for  grain  mashes  ;  the  mashf  enters  the  analyzer 
hot  after  having  passed  through  the  rectifier.  From  the  top  plates 
of  the  rectifier,  the  alcohol  vapor  passes  into  a  copper  condensing 
worm,  which  empties  into  a  small  box  with  glass  sides,  through  which 
the  density  of  the  liquid  may  be  observed  by  means  of  an  hydrometer 
floating  in  it.  The  box  is  locked  and  sealed  by  the  revenue  officer 
stationed  in  the  distillery,  and  the  distiller  has  no  access  to  the  liquor. 
It  overflows  into  tanks  where  it  is  gauged  by  the  revenue  officer  as 
"  high  wines."  It  contains  some  aldehyde  and  fusel  oil ;  the  latter, 
constituting  the  greater  part  of  the  impurities  present,  imparts  a 
nauseous  odor  and  taste,  and  is  removed  by  further  purification. 
The  raw  spirit  is  diluted  with  water  and  run  through  a  wood-charcoal 

*  The  old  pot  stills  are  now  used  for  the  distillation  of  certain  drinkable  spirits 
(especially  whiskey),  but  they  are  uneconomical  of  fuel  and  time. 

t  By  its  passage  through  the  still,  the  mash  is  entirely  deprived  of  its  alcohol, 
but  the  non-volatile  matter,  consisting  of  fats,  protein,  undecomposed  starch,  and 
other  non-nitrogenous  bodies,  flows  continuously  from  the  waste  pipe  of  the  still. 
This  residue  usually  contains  over  90  per  cent  water,  and  is  often  fed  as  "  slop  "  to 
cattle. 


FERMENTATION   INDUSTRIES  459 

filter  similar  in  form  to  the  bone-char  filter  used  for  glucose;  the 
charcoal  adsorbs*  the  fusel  oil.  Another  method  (that  of  Bang  and 
Ruffin)  is  to  treat  the  alcohol  with  caustic  soda  and  then  with  dilute 
sulphuric  acid  to  destroy  the  aldehydes ;  the  diluted  alcohol  is  then 
agitated  with  petroleum  distillates  boiling  slightly  above  100°  C. 
The  petroleum  oil  probably  absorbs  the  fusel  oil. 

The  dilute  purified  alcohol  is  then  rectified  in  a  still  provided 
with  a  column  or  dephlegmator  tower,  similar  to  the  Coupier  still 
or  French  column  apparatus,  Figs.  7  and  8.  Savalle's  apparatus 
is  largely  used  abroad.  Rectification  is  an  intermittent  process,  the 
still  being  entirely  emptied  and  cleaned  before  a  new  charge  is  intro- 
duced. The  boilers  are  very  large  and  are  usually  made  of  iron. 

The  products  of  the  distillation  are  divided  according  to  their 
character  and  percentage  of  alcohol  into :  — 

(a)  First  runnings,  consisting  of  some  alcohol,  with  aldehyde  and 
ethers. 

(b)  Alcohol  (cologne  spirits)  a  very  pure  distillate,  with  95  to  96 
per  cent  of  alcohol. 

(c)  Commercial  alcohol,  containing  80  to  95  per  cent  alcohol. 

(d)  Fusel  oil. 

These  distillates  are  separated  by  the  revenue  officer,  who  turns 
the  flow  from  one  receiver  into  the  next,  according  to  the  densities 
shown  by  the  hydrometer  floating  in  a  glass  box  similar  to  that  de- 
scribed on  p.  458  and  through  which  the  distillates  pass.  First  run- 
nings and  fusel  oil  are  usually  sold  to  chemical  works.  The  alcohol 
distillates  are  marketed  directly. 

The  Coffey  still  and  others  on  the  same  principle  are  well  adapted 
to  the  direct  production,  from  the  mash,  of  pure  alcohol,  or,  as  it 
is  generally  called  in  England,  "  silent  spirit,"  since  it  has  no  special 
odor  nor  flavor  to  distinguish  its  origin,  as  is  the  case  with  pot  stills. 

In  all  countries  the  manufacture  of  strongly  alcoholic  liquors  is 
made  a  means  of  raising  revenue  by  the  government.  Consequently 
these  industries  are  subject  to  constant,  and  often  annoying,  inter- 
ferences by  the  revenue  officials,  and  many  burdensome  laws  are 
enacted,  presumably  to  prevent  fraud.  In  this  country,  both  the 
malt  and  the  grain  used  in  the  mash  are  weighed  by  the  revenue 
officer,  the  time  of  fermentation  is  limited,  and  the  entire  process 
of  distillation  is  conducted  under  the  direct  supervision  of  the  in- 
spector. The  amount  of  crude  spirit  produced  is  gauged  by  the 
officer,  and  also  the  quantities  of  the  several  grades  of  rectified  alco- 
*  J.  Am.  Chem.  Soc.,  30  (1908),  1784.  W.  L.  Dudley. 


460  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

hoi  produced,  and  these  are  run  directly  from  the  still  into  storage 
tanks  in  the  government  storehouse.  From  these  tanks  it  is  drawn 
into  barrels  (which  must  be  new),  and  each  cask  is  at  once  gauged 
by  the  officers,  and  the  number  of  gallons  of  alcohol  contained  in 
the  liquor,  and  upon  which  the  tax  must  be  paid,  is  determined. 
The  cask  is  then  put  into  the  bonded  warehouse,  where  it  remains 
until  the  tax  is  paid  (but  not  longer  than  seven  years).  The  tax 
levied  is  $1.10  per  gallon  (231  cubic  inches)  of  "proof  spirit,"*  (or 
100  proof  alcohol)  or  $2.08  per  gallon  of  ordinary  95  per  cent  alco- 
hol. If  the  liquor  is  stronger  than  50  per  cent  alcohol  per  gallon,  it 
is  designated  as  "  above  proof,"  and  the  tax  is  estimated  on  the 
number  of  gallons  of  "  proof  spirit  "  which  can  be  made  from  it  by 
dilution.  If  under  50  per  cent  strength  ("  below  proof  "),  no  reduc- 
tion is  allowed,  and  it  is  taxed  as  if  of  "  proof  "  strength.  Thus  abso- 
lute alcohol  is  rated  as  "  100  above  proof,"  or  simply  "  200  proof  " ; 
ordinary  commercial  94  per  cent  alcohol  is  rated  as  188  proof. 

This  tax  was  a  heavy  burden  on  such  industries  as  use  alcohol 
for  manufacturing  purposes.  Most  governments  now  permit  the  man- 
ufacture of  "  denatured  "  alcohol  for  industrial  use,  and  this  is  free 
from  tax.  Various  substances  may  be  added  to  the  alcohol  for  the 
purpose  of  denaturing  or  rendering  it  undrinkable;  for  general  use 
10  gallons  of  crude  methyl  alcohol  and  J  gallon  of  benzine  are  mixed 
with  each  100  gallons  of  90  per  cent  ethyl  alcohol ;  or  to  each  100 
gallons  may  be  added  2  gallons  of  methyl  alcohol  and  J  gallon  of 
pyridine  bases  from  bone  oil.  For  various  special  industries  the  de- 
naturants  used  are  camphor,  nicotine,  methyl  acetate,  and  other  sub- 
stances. In  England  the  preparation  of  "  methylated  spirit,"  with 
10  per  cent  wood  spirits,  has  long  been  practised,  to  avoid  the  heavy 
tax  of  10s.  6d.  per  gallon  of  proof  spirit.* 

In  Germany  a  similar  provision  exists,  but  in  addition  to  wood 
spirits,  a  certain  amount  of  pyridine  (bone  oil)  must  also  be  added. 
This  gives  the  "  denaturated  "  alcohol  a  very  offensive  odor,  but  does 
not  injure  it  for  many  uses. 

Besides  starch  and  sugars  as  raw  materials  for  alcohol  making, 

*  "  Proof  spirit  shall  be  held  to  be  that  alcoholic  liquor  which  contains  one 
half  its  volume  of  alcohol  of  a  specific  gravity  of  seven  thousand  nine  hundred  and 
thirty-nine  ten  thousandths  (0.7939)  at  sixty  degrees  Fahrenheit."  —  U.  S.  Internal 
Revenue  Laws,  Jan.  1,  1900. 

By  act  of  the  English  Parliament,  proof  spirit  is  defined  as  "  Alcohol  of  such 
strength  that  13  gallons  of  the  spirit  have  the  same  weight  as  12  gallons  of  distilled 
water  at  10°  C.  (51°  F.)  "  Proof  spirit  contains  49.24  per  cent  of  absolute  alcohol 
by  weight.  The  English  gallon  is  the  Imperial  gallon  equivalent  to  10  Ibs.  of  water 
at  62°  F.  and  30  inches  barometric  pressure. 


FERMENTATION   INDUSTRIES  461 

cellulose  has  recently  been  brought  into  use  for  this  purpose.  Accord- 
ing to  the  process  of  A.  Classen,*  sawdust  or  shavings  are  treated 
under  6  to  7  atmospheres'  pressure  in  lead-lined',  rotary  digesters, 
with  sulphurous  acid;  the  cellulose  is  partly  converted  to  ferment- 
able sugar.  The  mass  is  systematically  lixiviated  with  hot  water, 
and  the  sugar  solution  neutralized  with  calcium  carbonate,  filtered, 
and  then  fermented  with  yeast.  The  "  mash  "  is  distilled.  Yields 
of  24  to  27  gallons  of  alcohol  per  long  ton  of  sawdust  are  claimed. 

The  waste  liquors  from  wood-pulp  making  by  the  "  sulphite  pro- 
cess "  after  treating  with  hot  sulphuric  acid  contain  fermentable 
sugars ;  f  attempts  have  been  made  to  neutralize  them  with  calcium 
carbonate,  and  then  ferment  for  alcohol.  The  industry  is  still  in  the 
experimental  state. 

The  fusel  oil  consists  mainly  of  amyl  alcohol,  with  some  butyl, 
propyl,  and  allyl  alcohols.  It  is  always  present  in  crude  spirits,  and, 
to  a  small  extent,  in  the  rectified  alcohol  and  liquors.  It  is  gen- 
erally supposed  to  have  a  very  destructive  action  on  the  health,  and 
its  complete  removal  from  liquors  has  always  been  insisted  upon. 
But  recent  experiments  t  tend  to  show  that,  aside  from  the  nauseous 
odor  and  flavor  which  it  imparts  to  the  liquor,  it  has  little,  if  any, 
injurious  effect  on  the  system.  The  results  ascribed  to  it  are  prob- 
ably due  to  common  alcohol.  Fusel  oil  (amyl  alcohol)  is  used  largely 
in  the  preparation  of  the  so-called  "  fruit  essences,"  organic  ethers, 
which  are  used  in  ice  cream,  soda  water,  sherbets,  etc. 

Alcohol  is  extensively  used  in  the  arts  as  a  solvent;  for  shellac 
varnishes ;  in  collodion  and  celluloid ;  for  making  transparent  soaps ; 
smokeless  powders  and  other  explosives ;  in  perfumery ;  for  making 
various  essences,  tinctures,  and  extracts  in  pharmacy;  for  vinegar 
making ;  and  in  chemical  manufacturing  for  preparing  ether,  chloral, 
chloroform,  ethyl  nitrite,  and  various  ethyl  derivatives,  especially 
for  use  in  the  coal-tar  dye  industry.  A  considerable  amount  is  used 
in  museums  for  preserving  anatomical  and  other  specimens. 

Whiskey  is  a  distilled  liquor  made  from  a  mash  of  fermented  bar- 
ley malt,  or  malt  and  other  cereals.  The  mash  is  prepared  as  de- 
scribed for  alcohol  (p.  457) ;  after  fermentation  it  is  distilled  from  a 
pot  still  (or  "  copper "),  and  the  distillate  condensed  in  a  worm, 
without  dephlegmation.  The  first  product,  called  "  low  wines,"  is 

*  U.  S.  Consular  Rep.,  Feb.  24,  1911.     Trans.  Am.  Inst.  Chem.  Eng.,  1911,  111. 

See  also,  Metallurgical  and  Chemical  Engineering,  1916  (14),  134. 

t  J.  Ind.  Eng.  Chem.,  1912  (4),  54. 

|  J.  Soc.  Chem.  Ind.,  1891,  312.     A.  H.  Allen, 


462  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

redistilled,  and  yields  foreshots,  whiskey,  and  feints,  while  spent  lees 
are  left  in  the  still.  The  foreshots  and  feints  are  redistilled  with  the 
next  charge,  while  the  whiskey  is  diluted  with  water  to  about  55 
per  cent  of  alcohol,  and  then  put  in  a  bonded  warehouse  to  age,  or 
until  the  revenue  tax  is  paid.  During  the  aging  the  fusel  oil  in  the 
liquor  is  formed  into  ethers,  thus  removing  the  nauseous  odor  and 
taste  of  the  raw  liquor,  and  imparting  to  it  a  pleasing  aroma.  This 
change  is  slow  and  the  longer  the  aging,  the  richer  the  flavor  of  the 
liquor  becomes.  When  first  distilled,  whiskey  is  colorless;  but  it 
takes  coloring  matter  from  the  wood  of  the  casks  while  aging,  and 
acquires  a  light  reddish-brown  shade.  This  color  is  now  generally 
imitated  by  adding  some  caramel. 

Scotch  whiskey  is  usually  made  from  malted  barley  mash,  which 
after  fermentation  is  distilled  in  pot  stills  heated  by  direct  fire. 
The  malt  used,  having  been  dried  over  a  fire  of  peat  and  coke,  ac- 
quires a  smoky  flavor,  which  passes  into  the  mash  and  thence,  on  dis- 
tillation, into  the  whiskey.  Frequently  some  "  silent  spirit  "  (p.  459) 
from  a  grain  mash  is  mixed  with  the  product  of  the  malt  distillation. 
Irish  whiskey  is  made  from  a  mash  containing  malt  and  some  un- 
malted  grain,  especially  rye,  barley,  wheat,  or  oats.  It  is  distilled  in 
large  pot-stills,  which  have  a  partial  condenser  on  the  neck  of  the 
still,  so  that  some  distillate  is  returned  to  the  still,  and  the  whiskey 
contains  about  67  per  cent  alcohol. 

Imitation  whiskey  is  often  made  by  "compounding,"  i.e.  di- 
luting grain  alcohol  with  water  to  about  55  per  cent  by  volume  and 
adding  caramel  with  small  quantities  of  flavoring  substances  and  essen- 
tial oils,  to  imitate  the  color,  odor,  and  taste  of  the  genuine  whiskey. 
An  empyreumatic  flavor  is  obtained  by  adding  a  few  drops  of  creosote 
to  each  cask. 

Gin  contains  about  52  per  cent  of  alcohol,  and  is  made  from  a 
fermented  grain  mash  in  much  the  same  way  as  alcohol,  but  the 
distilled  liquor  is  left  colorless,  and  is  flavored  by  distilling  in  pot  stills 
with  juniper  berries,  anise  seed,  coriander,  cardamon  seed,  calamus 
root,  or  fennel.  The  best  gin  is  made  in  Holland,  at  Schiedam,  from 
rye  mash,  and  is  distilled  only  in  pot  stills,  with  juniper  berries. 

Brandy  is  made  by  distilling  wine,  or  the  fermented  juice  of  other 
fruit,  such  as  apples,  peaches,  cherries,  blackberries,  etc.  The  best 
brandy  (Cognac)  is  made  by  distilling  a  good  quality  of  white  wine, 
but  much  inferior  stuff  is  made  by  distilling  low  grades  of  red  wine. 
It  is  customary  to  leech  the  solid  residues  from  wine-pressing  with 
water,  and  to  ferment  the  liquid  so  obtained;  this  is  then  distilled 


FERMENTATION   INDUSTRIES  463 

for  inferior  brandy.  Cheap  brandies  are  distilled  directly  from  the 
wine,  but  fine  grades  are  rectified  once  or  twice.  The  distillate  is 
colorless,  but  takes  color  from  the  casks.  It  is  also  customary  to 
add  caramel.  Brandy  contains  from  47  to  54  per  cent  of  alcohol,  by 
volume,  and  owes  its  peculiar  flavor  to  cenanthic  ether.  Pot  stills 
are  always  used  in  order  to  preserve  the  flavors.  Cherry  brandy  is 
extensively  made  in  southern  Germany,  where  it  is  called  Kirsch- 
wasser.  Some  of  the  pits  are  crushed  and  added  to  the  fermented 
juice,  thus  flavoring  the  product  with  bitter  almond  and  prussic  acid. 
Imitation  brandy  is  made  from  grain  alcohol  by  diluting  and  adding 
various  flavoring  matters  (oenanthic  ether,  bitter  almonds,  catechu, 
etc.),  and  coloring  with  caramel. 

Rum  is  made  from  fermented  molasses  or  megass  (macerated 
crushed  sugar  cane).  It  is  twice  distilled,  and  the  new  rum  is  color- 
less and  has  a  disagreeable  odor,  which  is  removed  by  treating  with 
charcoal  and  storing  for  a  long  time.  It  is  often  colored  with  burnt 
sugar.  It  contains  about  72  per  cent  of  alcohol,  and  its  flavor  is 
due  to  ethyl  acetate  and  butrate.  Jamaica  rum  is  said  to  be  flavored 
by  putting  sugar  cane  leaves  in  the  still.  Ethyl  butrate  is  made  on 
a  large  scale,  and  sold  as  "  rum  essence,"  to  be  used  in  making  imi- 
tation rum  from  grain  spirit. 

Liqueurs  and  cordials  are  usually  strong  alcoholic  beverages  com- 
pounded from  grain-  alcohol,  with  various  flavoring  essences.  They 
are  usually  flavored  with  sugar  cane. 

Arrack  is  made  by  distilling  toddy,  the  fermented  juice  of  the 
cocoanut  palm.  It  is  sometimes  flavored  with  poppy  or  hemp  leaves, 
or  stramonium  juice.  A  distilled  liquor  made  from  malted  rice  and 
molasses  is  often  sold  as  arrack. 

Absinthe  is  made  in  much  the  same  way  as  gin,  but  is  flavored 
with  wormwood. 

VINEGAR 

Next  to  the  alcoholic  fermentation  in  technical  importance  is  the 
acetic  fermentation,  which  is  caused  by  a  group  of  bacteria.  These 
micro-organisms  cause  the  oxidation  of  the  alcohol,  probably  into 
aldehyde,  and  ultimately  into  acetic  acid,  thus :  — 

2  C2H5OH  +  O2  =  2  C2H4O  +  2  H2O. 
2  C2H4O  +  O2  =  2  C2H4O2. 

The  specific  acetic  ferment  is  Bacterium  aceti,  but  the  related 
species,  B.  Pasteurianuin,  B.  xylinum,  and  B.  Kutzingianum,  doubtless 
cause  more  or  less  oxidation  of  the  alcohol.  For  this  oxidation  the 


464  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

liquid  must  not  contain  more  than  10  per  cent  of  alcohol,  and  certain 
nitrogenous  matters  suitable  for  the  nourishment  of  the  ferment 
must  be  present. 

The  materials  used  for  fermented  vinegar  are  cider,  wines,  decoc- 
tions made  from  malt,  beer  which  has  not  been  boiled  with  hops, 
beet  sugar  solutions,  diluted  alcohol  mixed  with  malt  infusion,  and 
occasionally  glucose  or  molasses.  The  acetic  ferment  propagates 
rapidly  in  a  liquid  containing  from  2  to  3  per  cent  of  alcohol,  nitrog- 
enous matter,  and  phosphate  of  potassium,  calcium,  or  ammonium, 
if  the  temperature  is  kept  between  20°  and  35°  C.  A  thick  film, 
or  skin,  forms  on  the  surface  of  the  liquid,  and  finally  sinks,  owing 
to  its  increasing  weight,  forming  the  "  vinegar  mother  " ;  then  the 
formation  of  acid  ceases.  If  the  fermentation  is  very  active  after 
the  alcohol  is  all  converted,  the  resulting  acetic  acid  may  itself 
be  attacked  and  decomposed  into  water  and  carbon  dioxide.  This, 
however,  does  not  take  place  if  a  fresh  supply  of  alcoholic  liquor  is 
added.  Under  the  most  favorable  conditions  the  ferment  cannot  live 
in  a  liquid  containing  much  more  than  13  per  cent  of  acetic  acid. 

In  the  Orleans  process  of  making  vinegar  from  wine,  oak  casks  of 
about  300  litres'  capacity  are  used.  The  cask  is  filled  about  one-third 
full  of  strong  vinegar  containing  some  ferment,  and  about  10  litres 
of  wine  (previously  filtered  through  beechwood  shavings  until  clear) 
are  added,  and  the  whole  allowed  to  stand  at  a  temperature  of  from 
25°  to  30°  C.  After  about  eight  days  the  wine  has  soured,  and  another 
portion  of  10  litres  of  wine  is  added.  This  process  is  repeated  until 
the  cask  is  about  half  full,  when  about  one-third  of  the  vinegar  is 
drawn  off,  and  the  process  of  adding  fresh  wine  is  resumed.  This 
goes  on,  under  favorable  circumstances,  for  several  years,  until  the 
cask  becomes  too  full  of  sediment ;  then  it  is  emptied,  and  thoroughly 
cleaned  by  washing  and  scalding  with  hot  vinegar.  The  casks  have 
openings  at  the  top  for  the  admission  of  air,  and  the  fermentation  is 
largely  spontaneous. 

The  action  of  the  ferment  may  be  checked  if  the  temperature 
falls  too  low;  or  if  the  wine  added  is  very  low  in  alcohol,  it  may 
not  support  the  ferment,  and  the  vinegar  is  decomposed  into  water 
and  carbon  dioxide.  The  ferment  may  also  be  weakened  or  destroyed 
by  the  presence  of  vinegar  eels,  Anguillula  aceti,  a  species  of  micro- 
scopic worm,  which  deprives  the  ferment  of  the  oxygen  needed  for 
its  propagation. 

The  Orleans  process  is  slow,  but  the  resulting  vinegar  has  a  fine 
flavor  and  aroma. 


FERMENTATION   INDUSTRIES  465 

Pasteur  suggested  a  modification  of  the  above  process,  in  which 
the  ferment  is  cultivated  in  a  suitable  liquid,  and  the  alcoholic  liquid 
is  added  regularly  when  the  "  mother  "  is  well  started.  When  the 
acid  formation  becomes  slow,  the  "  mother  "  is  collected  and  washed, 
and  used  to  start  a  new  fermentation. 

The  "  quick  vinegar  process  "  is  now  generally  practised  for  fer- 
menting malt  decoctions,  diluted  alcohol,  or  the  extract  from  any 
fermented  mash.  The  liquid  should  be  clear,  and  free  from  any 
sediment  or  slime.  The  fermentation  is  carried  on  in  tall  vats,  or 
casks,  about  12  feet  high  by  5  feet  in  diameter.  These  have  perfo- 
rated false  bottoms,  on  which  rests  the  filling  of  beechwood  shavings, 
reaching  nearly  to  the  top  of  each  cask.  Over  the  shavings,  a  few 
inches  below  the  cover  of  the  cask,  is  a  perforated  wooden  plate, 
through  the  holes  of  which  short  pieces  of  twine  are  drawn ;  4  or  5 
glass  tubes  are  set  in  this  plate,  to  permit  the  upward  passage  of  the 
air.  The  beech  shavings  are  boiled  in  water,  and  then  soaked  in 
strong  vinegar,  before  filling  into  the  vat.  Their  purpose  is  to 
spread  the  liquid  into  thin  films,  so  that  the  oxidation  may  be 
rapid.  They  also  serve  as  points  of  attachment  for  the  ferment. 
The  liquid  to  be  fermented,  a  mixture  of  dilute  alcohol  and  vinegar, 
is  fed  in  a  slow  stream  on  to  the  top  of  the  cover,  through  which  it 
percolates,  dripping  from  the  ends  of  the  twine  upon  the  shavings. 
It  comes  in  contact  with  the  ferment  on  the  shavings,  and  with  the 
current  of  air  passing  up  through  the  mass,  and  the  alcohol  is  rapidly 
oxidized  into  acetic  acid.  The  temperature  within  the  vat  rises, 
causing  the  air  to  rise  and  escape  through  the  openings  in  the  top, 
while  fresh  air  enters  through  holes  in  the  sides  of  the  vat,  just  on  a 
level  with  the  false  bottom,  thus  causing  a  continual  circulation  of 
fresh  air  within  the  vessel.  The  temperature  is  shown  by  a  ther- 
mometer, and  is  kept  as  near  30°  C.  as  possible,  by  regulating  the 
temperature  of  the  air  admitted  into  the  cask.  If  allowed  to  go  too 
high,  much  alcohol  is  lost  by  evaporation,  and  the  vinegar  is  weak. 
Too  rapid  an  air  current  also  evaporates  much  alcohol.  The  vinegar 
formed  collects  under  the  false  bottom,  and  flows  out  through  a  siphon. 

If  the  liquor  does  not  contain  more  than  4  per  cent  of  alcohol,  it 
may  all  be  converted  by  one  passage  through  the  vat,  but  the  result- 
ing vinegar  is  weak.  Hence  it  is  customary  to  add  more  alcohol, 
and. run  the  liquor  through  the  cask  again.  Or,  as  is  often  done,  it 
flows  through  a  series  of  vats. 

Exact  regulation  of  the  strength  and  flow  of  alcoholic  liquid, 
and  of  the  amount  of  air  admitted,  is  essential  to  successful  work- 


466  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

ing.  Pure  air  and  good  ventilation  of  the  room  are  also  necessary. 
Considerable  alcohol  is  lost  by  evaporation,  amounting,  even  in  good 
work,  to  about  15  to  20  per  cent  of  that  in  the  original  liquid. 
The  air  leaving  the  converters  is  often  washed  with  water  to  recover 
the  vaporized  alcohol  and  acetic  acid.  On  an  average,  the  vinegar 
produced  contains  about  6  per  cent  acetic  acid,  which  may  be  in- 
creased to  10  or  12  per  cent  by  proper  regulation  of  the  process; 
there  is,  however,  a  consequent  diminished  yield  of  vinegar.  The 
time  required  to  produce  finished  vinegar  is  from  8  to  12  days.  The 
amount  of  alcohol  added  must  be  so  regulated  that  the  liquid  leaves 
the  vat  still  containing  a  small  percentage  of  unchanged  alcohol, 
for,  if  it  is  all  converted,  the  oxidation  extends  to  the  acetic  acid, 
and  some  may  be  lost  through  decomposition  into  water  and  carbon 
dioxide.  Many  accidents  cause  the  process  to  go  wrong,  and  much 
care  is  necessary  to  secure  regularity  of  product  and  yield.  If  vine- 
gar eels  appear,  it  is  customary  to  kill  them  by  adding  hot  vinegar 
until  the  temperature  of  the  vinegar  running  out  of  the  cask  has  risen 
to  50°  C. 

The  vinegars  made  from  different  sources  vary  in  color,  taste, 
specific  gravity,  and  other  properties. 

Cider  vinegar  is  usually  made  by  spontaneous  fermentation  of 
cider  in  barrels  with  open  bungs.  Sometimes  "  mother  "  is  added 
to  hasten  the  action.  It  is  yellow  or  brown  in  color,  has  an  odor 
resembling  apples,  and  contains  malic  acid. 

Wine  vinegar  is  light  yellow  or  red,  according  as  it  is  made  from 
white  or  red  wine,  that  made  from  the  former  being  considered  the 
better.  It  contains  tartaric  acid,  and  some  acid  potassium  tartrate, 
with  other  matters  derived  from  the  wine,  some  of  which  influence 
the  flavor  of  the  product.  It  has  a  particularly  agreeable  aroma  and 
taste,  and  is  considered  the  finest  for  table  use. 

Malt  and  beer  vinegars  are  brown  in  color,  and  contain  dextrin 
and  protein,  and  other  extractive  matters,  together  with  acetic  ether, 
which  impart  peculiar  odors  and  flavor  to  them.  They  also  contain 
phosphates  and  other  mineral  matter. 

Spirit  vinegars,  made  from  diluted  alcohol,  are  nearly  colorless, 
and  since  they  contain  little  or  none  of  the  extractive  matter  present 
in  fruit  or  malt  vinegars,  they  lack  much  of  the  flavor  and  odor  of 
these.  Sometimes  they  are  colored  with  caramel,  and  are  often 
flavored  with  one  or  more  of  the  characteristic  ingredients  of  cider, 
wine,  or  malt  vinegars,  and  sold  under  these  names. 

Very  weak  vinegar  will  not  bear  much  agitation  nor  handling 


FERMENTATION   INDUSTRIES  467 

without  decomposition ;  it  is  often  the  practice  to  add  a  certain 
amount  of  sulphuric  acid,  under  the  pretence  of  preserving  the 
vinegar  when  shipped.  Good  vinegar,  however,  is  never  treated 
in  this  way  by  reputable  makers. 

Imitation  vinegar  is  often  made  from  dilute  acetic  acid  derived 
from  wood  distillation.  This  is  colored  with  caramel,  and  gen- 
erally flavored  with  acetic  ether;  but  usually  contains  no  phos- 
phates, tartrates,  nor  other  substances  characteristic  of  true  vinegar. 
Traces  of  empyreumatic  matter  are  often  present,  which  may  give 
it  a  disagreeable  flavor. 

Vinegar  is  chiefly  consumed  as  a  condiment,  or  used  for  making 
pickles. 

LACTIC  ACID 

A  fermentation  of  some  technical  importance  is  that  produced  by 
certain  bacteria,  especially  Bacterium  acidi  lactici,  by  which  sugars 
are  converted  into  lactic  acid  :  — 

C6H1206  =  2  C2H4(OH)COOH. 

These  ferments  are  generally  distributed  on  the  surface  of  grains, 
fruits,  and  malt,  thus  finding  access  to  mashes  and  worts ;  under  favor- 
able circumstances  they  grow  exceedingly  rapidly,  and  cause  souring 
of  the  liquid.  But  since  they  cease  to  propagate  after  the  liquid 
contains  about  1  per  cent  of  lactic  acid,  and  as  this  acid  is  a  good 
protection  against  the  development  of  other  bacteria,  while  it  has 
but  little  effect  upon  yeast,  it  is  often  customary  to  allow  the  lactic 
fermentation  to  take  place  in  connection  with  the  alcoholic,  especially 
in  grain  mashes  for  alcohol. 

Lactic  acid,  CH3  •  CH(OH)  •  COOH,  is  prepared  by  fermenting  a 
sugar  solution,  and  neutralizing  the  acid,  as  soon  as  formed,  with 
calcium  carbonate.  The  solution  of  calcium  lactate  is  concentrated, 
and  the  salt  decomposed  with  sulphuric  acid. 

Lactic  acid  forms  a  syrupy  liquid  which  is  now  used  in  dyeing  and 
calico  printing  as  a  substitute  for  tartaric  and  citric  acids,  and  for 
deliming  skins  previous  to  tanning.  Antimony  lactate  is  used  in 
place  of  tartar  emetic  in  mordanting. 

REFERENCES 

The  Chemistry  of  Wine.     G.  J.  Mulder.     Translated  by  H.  Bence  Jones. 

London,  1857.     (Churchill.) 

Lehrbuch  der  Gahrungs  Chemie.     Adolf  Mayer,  Heidelberg,  1874. 
On  Fermentation.     P.  Schutzenberger,  New  York,  1876.     (Appleton.) 


468  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

TraitS  general  des  Vins  et  de  leurs  Falsifications,     fi.  Viard,  Paris,  1884. 

Die  Bereitung,  Pflege  und  Untersuchung  des  Weins.     J.  Nessler,  Stutt- 
gart, 1889. 

The  Micro-organisms  of  Fermentation.     A  Jorgenson.     Translated  by 
H.  T.  Brown.     London,  1889. 

Traite  pratique  de  1'Art  de  Faire  le  Vin.     Frederic  Cazalis,  Paris,  1890. 

L'art  de  Faire  le  Vin  avec  les  Raisins  sees.     J.  F.  Audibert,  Paris,  1891. 

fitudes  sur  la  Biere.     M.  L.  Pasteur,  Paris,  1876.      (Gauthier-Villars.) 

Lehrbuch  der  Bierbrauerei.    Carl  Lintner,  Braunschweig,  1878.    (Vieweg.) 

Gahrungs-Chemie    fur    Praktiker.     Josef    Bersch,    Berlin.     (Wiegandt, 

Hempel,  und  Parey.) 

Vol.  I.     Die  Hefe  und  die  Gahrungs  Erscheinungen.     1879. 
Vol.  II.     Fabrikation  von  Malz,  Malzextract  und  Dextrin.     1880. 
Vol.  III.     Die  Bierbrauerei.     1881. 

The  Brewer,  Distiller,  and  Wine  Manufacturer.     John  Gardner,  Phila- 
delphia, 1883.     (Blakiston,  Son  &  Co.) 

The  Theory  and  Practice  of  Modern  Brewing.     Frank  Faulkner.     3d  ed. 
London,  1888.     (F.  W.  Lyon.) 

Handbuch   der  Bierbrauerei.     Conrad  Schneider  u.   Gottlieb  Behrend, 
Halle,  a.  S.,  1891.     (W.  Knapp). 

Chemistry  in  the  Brewing  Room.     Chas.  H.  Piesse,  London,  1891. 

Manual  of  Brewing.     E.  G.  Hooper.     4th  ed.     London,  1891. 

A  Textbook  of  the  Science  of  Brewing.     E.  R.  Moritz  and  G.  H.  Morris, 
London,  1891.     (E.  &  F.  N.  Spon.) 

La  Biere.     L.  Lindet,  Paris,  1892  (?). 

Les  Distilleries.     M.  Desire  Savalle,  Paris,  1881.     (G.  Masson.) 

A  Practical  Treatise  on  the  Raw  Materials  and  the  Distillation  and  Recti- 
fication of  Alcohol.     Wm.  T.  Brannt,  Philadelphia,  1885. 

L'Alcool.     Albert  Larbaletrier,  Paris,  1888.      (Bailliere  et  Fils.) 

A  Treatise  on  Alcohol,  with  Tables  of  Spirit-Gravities.     Thomas  Steven- 
son, London,  1888.     (Gurney  &  Jackson.) 

Traite  de  la  Distillation.     J.  Fritsch  et  E.  Guillemin,  Paris,  1890. 

La  Fabrication  des  Liqueurs  et  des  Conserves.    M.  Ch.  Girard,  Paris,  1890. 

Nouveau  Manuel  complet  de  la  Distillation  des  Grains  et  des  Melasses. 
Albert  Larbaletrier  et  M.  F.  Malepeyre,  Paris,  1890. 

Les  Appareils  de  Distillation  et  de  Rectification,   fimile  Barbet,  Paris,  1890. 

Traite  de  la  Fabrication  des  Liqueurs  et  de  la  Distillation  des  Alcools. 
P.  Duplais,  2  vols.,  7me  ed.,  Paris,  1900.     (Gauthier-Villars.) 

Das  Flussaureverfahren  in  der  Spiritusfabrikation.     M.  Maercker,  Berlin, 
1891. 

La  Rectification  de  I'Alcool.     E.  Sorel,  Paris,  1894  (?).     (G.  Masson.) 

Chemie  du  Distillateur.     M.  P.  Guichard,  Paris,  1895.     (Bailliere.) 

Industrie  de  la  Distillation,  Levures  et  Alcools.     M.  P.  Guichard,  Paris, 
1897. 

Etudes  sur  le  Vinaigre.     M.  Pasteur,  Paris,  1868. 

Acetic  Acid  and  Vinegar,  etc.     John  Gardner,  London,  1885.     (Churchill.) 

A  Treatise  on  the  Manufacture  of  Vinegar.     Wm.  T.  Brannt,  Phila.,  1890. 

Die  Essigfabrikation.     J.  Bersch.     5te  Auf.     Wien,  1901. 

The  Principles  and  Practice  of  Brewing.     W.  J.  Sykes,  London,  1897. 

The  Laboratory  Text-Book  for  Brewers.     L.  Briant,  2d  ed.,  London,  1898. 

The  Soluble  Ferments  and  Fermentation.     J.  Reynolds  Green,  Cambridge, 
1899. 

Les  Fermentations  Rationnelles,  par  Georges  Jacquemin,  1900. 

Micro-organisms  and  Fermentation.   Alfred  Jorgensen.    Trans,  by  Alex.  K. 
Miller  and  A.  E.  Lermholm.   3d  ed.,  London,  1900.    (Macmillan  &  Co.) 

Ferments  and  their  Actions.     Carl  Oppenheimer.     Trans,  by  C.  Ains- 
worth  Mitchell.     London,  1901.     (Griffin  &  Co.) 

Manual  of  Alcoholic  Fermentation.     By  Chas.  B.  Matthews,  London, 
1901. 

Enzymes  and  their  Applications.     By  J.  Effront.     Trans,  by  Samuel  C. 
Prescott,  New  York,  1902.     (Wiley  &  Sons.) 


FERMENTATION   INDUSTRIES  469 

Handbuch  der  Spiritusfabrikation.     M.  Maercker.     8te  Auf.     1903. 
The    Chemical    Changes    and    Products   resulting   from    Fermentations. 

R.  H.  A.  Plimmer, 'London,  1903.      (Longmans,  Green  &  Co.) 
Manufacture  and  Exportation  of  Alcoholic  Beverages  and  Canned  Goods. 

H.  W.  Wiley.     Bui.  No.  102,  Bureau  of  Chemistry,  U.  S.  Dep't  of 

Agriculture,  1906. 
Regulations  and  Instructions  concerning  the  Tax  on  Distilled    Spirits. 

No.  7,  Revised  Sept.  16,  1908.     U.  S.  Internal  Revenue. 
The  Nature  of  Enzyme  Action.     W.  M.  Bayliss,  London,  2d  ed.,  1911. 
Alcoholic  Fermentation.     Arthur  Harden,  London,  1911. 


EXPLOSIVES 

Explosives  are  chemical  compounds  or  mechanical  mixtures  which 
are  capable  of  very  rapid  decomposition  or  combustion,  upon  the 
application  of  a  shock,  or  of  a  small  amount  of  heat.  Through 
the  agency  of  chemical  action  they  suddenly  generate  large  volumes 
of  gas,  which  is  heated  to  a  high  temperature  at  the  moment  of  liber- 
ation. Explosives  comprise  gases,  liquids,  and  solids.  Explosive 
gas  mixtures  will  not  be  considered  here,  since,  except  in  gas- 
engines,  they  have  no  technical  application,  though  often  introducing 
dangerous  complications  in  certain  technical  processes.  Finely  di- 
vided organic  matter,  or  oxidizable  substances  (e.g.  magnesium  powder) 
suspended  in  air,  may  if  ignited  cause  violent  "  dust  explosions," 
which  constitute  a  serious  danger  in  various  manufacturing  processes. 
Liquid  explosives,  excepting  only  nitroglycerine,  which  is  seldom  used 
in  the  liquid  condition,  have  little  or  no  industrial  importance,  since 
being  extremely  sensitive  to  shocks  and  heat,  they  are  too  dangerous 
to  handle  or  transport;  for  the  same  reasons  many  endothermic 
bodies,  such  as  the  halogen  compounds  of  nitrogen,  and  the  diazo- 
bodies  are  not  employed. 

When  the  combustion  takes  place  under  such  conditions  that  the 
gases  formed  cannot  readily  escape,  a  very  high  pressure  is  suddenly 
developed,  owing  to  the  great  amount  of  heat  generated.  Some 
explosives  can  be  fired  by  heat  or  ordinary  shock,  but  others  require 
the  sudden  and  excessive  pressure  developed  by  certain  violent  ex- 
plosives called  "  detonators,"  such  as  the  fulminates  of  mercury  or 
silver,  and  the  azide  of  lead.  Detonators  have  extreme  shattering 
power.  Detonation  is  necessary  to  initiate  the  complete  break-down 
of  certain  relatively  stable  molecules ;  it  is  not  unlikely  that  detona- 
tion produces  atomic  vibrations  in  the  molecule  itself  sufficient  to 
start  an  excessively  rapid  disintegration. 

The  energy  of  an  explosive  is  mainly  determined  by  the  amount 
of  gaseous  products  formed  by  its  decomposition,  the  rapidity  of 
their  evolution,  and  the  temperature  to  which  these  gases  are  heated. 
It  has  been  calculated  that  the  explosion  of  one  kilogram  of  dynamite 
in  the  form  of  a  cube,  measuring  9  cm.  on  the  side,  occupies  -g-Q^inr  °f 
a  second,  while  the  same  weight  of  ordinary  black  powder  requires 
T^  of  a  second.  But  the  volume  of  gas  set  free  by  the  dynamite  is 
about  530  liters  when  reduced  to  0°  C.  and  at  760  mm.  pressure; 

470 


EXPLOSIVES  471 

while  the  gas  from,  gunpowder,  under  the  same  conditions  of  tem- 
perature and  pressure,  amounts  to  about  270  liters.  Moreover,  the 
temperature  of  the  gas  from  the  dynamite  is  very  much  higher  than 
is  that  from  gunpowder. 

Nearly  all  explosions  caused  by  chemical  action  are  merely  rapid 
oxidations  of  substances  containing  carbon,  hydrogen,  or  nitrogen. 
The  slower  the  oxidation  the  weaker  the  explosion,  while  for  the 
most  energetic  action  the  combustion  must  be  practically  instanta- 
neous. The  speed  of  the  oxidation  depends  largely  on  the  size  of 
the  particles  of  the  explosives,  and  also  upon  their  composition. 
Chemically  homogeneous  substances  are  usually  more  powerful  ex- 
plosives than  the  most  carefully  prepared  mixtures,  since 'in  the  former 
the  combustion  is  propagated  from  molecule  to  molecule  more  rapidly. 

Explosives  which  decompose  suddenly  cause  a  very  different 
result  than  those  which  are  slow-burning.  The  former,  even  when 
exploded  in  the  open  air,  have  a  shattering,  action  upon  any  sub- 
stance with  which  they  are  in  contact.  They  are  used  in  hard-rock 
blasting,  especially  where  large  pieces  of  the  stone  are  not  desired, 
or  when  the  rock  is  full  of  cracks  or  seams;  fewer  drill  holes  are 
needed,  and  the  rock  is  shattered  for  some  distance  away  from  the 
blast.  But  for  military  purposes,  for  quarrying  and  blasting  in  soft 
rock  or  coal,  slow-burning  powder  is  preferable  to  the  more  powerful 
dynamite. 

Gunpowder  is  a  mechanical  mixture,  and  is  the  oldest  and  a  very 
important  explosive.  A  doubtful  tradition  assigns  its  discovery  to 
Berthold  Schwartz,  a  monk  at  Freiburg,  Germany,  in  the  fourteenth 
century.  It  was  used  at  the  battle  of  Crecy  in  1346,  and  again  at 
Augsburg  in  1353.  It  was  probably  derived  from  the  formula  of 
the  "  Greek  fire  "  of  the  Orient.  Its  constituents  are  potassium 
nitrate,  sulphur,  and  charcoal.  Since  these  must  be  pure,  the  manu- 
facturer generally  purifies  them.  Only  roll  brimstone  is  used,  and 
this  is  sublimed  in  Dejardin's,  or  other  similar  apparatus.  The 
flowers  of  sulphur,  which  first  distil  over,  are  contaminated  with 
sulphur  dioxide,  and  are  redistilled  with  a  new  portion  of  sulphur. 
The  purified  brimstone  is  finely  ground  in  ball-mills,  disintegrators, 
or  under  edge-runners,  sometimes  with  the  addition  of  a  part  of  the 
charcoal.  Bronze  balls  are  used  in  the  mill;  the  dust  is  carefully 
sifted. 

The  nitre  is  purified  from  chloride,  or  sodium  nitrate,  by  several 
recrystallizations  from  pure  water,  the  solution  being  stirred  while 
cooling  in  order  to  separate  fine  crystals.  These  are  wa'shed  with 


472  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

water  while  in  the  centrifugal  machine,  or  on  a  draining  platform. 
They  are  not  usually  dried  before  mixing. 

Carbon  for  gunpowder  is  best  obtained  from  charcoal  prepared 
from  light,  soft  woods,  such  as  willow,  poplar,  alder,  or  buckthorn. 
Young  trees  cut  in  the  spring  when  full  of  sap  are  preferred.  The 
bark  is  removed,  and  the  wood  stored  for  about  two  years  until 
thoroughly  dried.  It  is  then  carbonized  in  sheet-iron  cases,  which 
are  heated  in  retorts,  from  which  the  products  of  distillation  may  be 
collected  or  not,  as  desired.  The  temperature  of  the  carbonization 
depends  upon  the  kind  of  powder  to  be  made.  For  black  powder 
it  ranges  from  350°  to  500°  C. ;  for  brown  powder  it  does  not  exceed 
280°  C.  When  the  carbonization  is  ended,  the  cases  are  removed  and 
allowed  to  cool  before  they  are  opened.  The  charcoal  is  then  sorted 
to  secure  uniformity  in  the  product,  and  is  stored  for  some  time 
before  grinding,  to  allow  it  to  absorb  all  the  oxygen  possible ;  other- 
wise spontaneous  combustion  of  the  powdered  charcoal  is  liable  to 
occur. 

Charcoal  for  black  powder  contains  about  80  to  90  per  cent  car- 
bon, 5  to  7.5  per  cent  oxygen,  and  2  to  3  per  cent  hydrogen.  That 
for  brown  powder  contains  about  70  to  75  per  cent  carbon,  20  to 
35  per  cent  oxygen,  and  4.5  to  5  per  cent  hydrogen.  The  residue, 
in  each  case,  is  ash. 

The  ground  materials  are  weighed,  due  allowance  being  made  for 
the  moisture  in  the  nitre,  and  then  put  into  the  mixing  machine ; 
this  consists  of  a  gun-metal  cylinder  revolving  around  a  horizontal 
shaft,  which  turns  in  a  direction  opposite  to  that  of  the  cylinder,  and 
carries  arms  which  stir  up  the  mass  as  they  revolve.  After  mixing, 
the  "  green  charge  "  is  sifted  again,  moistened  with  from  5  to  6  per 
cent  of  water,  and  spread  on  the  bed  of  the  incorporating  mill.  This 
is  an  edge-runner,  having  iron  or  stone  rolls,  which  travel  on  a  bed 
of  bronze  or  stone.  The  rollers  are  usually  about  15  inches  wide, 
and  weigh  3  to  4  tons  each.  They  make  7  or  8  revolutions  per  min- 
ute, and  the  usual  time  of  grinding  a  charge  is  from  3  to  6  hours. 
Travelling  wooden  scrapers  push  the  charge  from  the  sides  of  the 
bed  into  the  path  of  the  rollers.  The  charge  is  kept  moist  during  the 
incorporating,  but  explosions,  the  causes  of  which  are  not  easy  to 
discover,  occur  frequently.  Consequently,  the  mill  is  arranged 
to  run  as  nearly  automatically  as  possible,  and  the  workmen  leave 
the  building  during  this  process. 

The  "  mill-cake  "  coming  from  the  incorporating  mill  is  lumpy,  and 
is  reduced  to  fine  powder  by  passing  through  the  "  breaking-down 


EXPLOSIVES  473 

machine."  This  consists  of  two  sets  of  gun-metal  rolls,  placed  one 
over  the  other,  the  'upper  set  being  corrugated  and  the  lower  pair 
smooth.  These  rolls  are  set  in  movable  bearings,  which  allow  them 
to  separate  slightly,  in  case  of  any  excessive  pressure.  The  mill- 
cake  is  thus  reduced  to  a  fine  meal,  containing  from  1  to  4  per  cent 
of  moisture.  This  is  put  into  wood-lined  metal  frames,  and  pressed  in 
an  hydraulic  press  to  the  desired  density,  usually  300  to  450  pounds 
pressure  per  square  inch  being  applied.  The  press-cake  so  formed  may 
be  as  thick  as  desired,  for  special  purposes,  but  is  usually  about  one- 
half  an  inch  thick.  For  common  powder,  this  compact,  dense  press- 
cake  is  put  through  the  granulator,  which  consists  of  two  or  three  pairs 
of  grooved  or  toothed  rolls  of  gun-metal ;  between  them  are  inclined 
oscillating  sieves,  which  sift  the  material  from  one  pair  of  rolls  and  de- 
liver the  coarse  particles  to  the  next  pair,  where  they  are  again  crushed. 
Under  the  whole  series  of  rolls  are  two  sieves,  the  upper  having  a  No.  10 
mesh  and  the  lower  having  a  No.  20  mesh.  These  remove  the  coarse 
particles,  and  the  fine  grains  are  run  over  several  finer  meshed  sieves, 
to  obtain  various  grades  of  sporting  powder,  and  dust.  The  grains 
thus  separated  are  glazed;  i.e.  the  powder  is  placed  in  revolving 
wooden  drums,  in  which,  by  rubbing  against  each  other,  the  sharp 
corners  and  edges  are  worn  off.  Powder  which  has  been  heavily 
pressed  is  hard  and  dense,  and  takes  considerable  polish.  For  com- 
mon grades,  it  is 'customary  to  add  about  one  ounce  of  graphite  to 
every  100  pounds  of  powder  in  the  glazing  drum.  This  coats  the 
grains  and  fills  the  pores,  thus  protecting  them  from  moisture  and 
atmospheric  influences. 

After  glazing,  the  dust  is  removed  by  sifting,  and  the  powder  is 
dried.  It  is  spread  in  wooden  frames  having  cloth  bottoms,  and 
these  are  placed  in  racks  in  a  room  through  which  a  current  of  warm 
air  is  circulating,  and  which  is  kept  at  a  constant  temperature  of  35° 
to  60°  C.,  according  to  the  nature  of  the  powder.  The  temperature  is 
raised  slowly,  and,  after  drying,  the  powder  is  cooled  slowly,  the  en- 
tire process  requiring  about  24  hours.  Sometimes  the  powder  is  dried 
in  a  stream  of  cold  air  which  has  been  passed  over  calcium  chloride, 
sulphuric  acid,  or  quicklime,  to  dry  it  before  it  enters  the  dry-room. 
Many  schemes  have  been  devised  for  drying  powder  in  vacuum,  but 
they  have  not  proved  practical.  After  drying,  the  powder  is  given 
a  final  glazing,  and  is  sifted  to  remove  the  dust,  and  is  then  ready  for 
use. 

Special  forms  of  powder  are  used  for  particular  purposes.  The 
coarse  grains  are  used  for  blasting,  the  fine  grains  for  small  arms, 


474  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

while  the  fine  dust  is  not  desirable  for  any  purpose,  except  in  fire- 
works. Pebble  and  prismatic  powders  are  chiefly  used  for  ordnance. 
The  press-cakes  of  the  "  green  charge  "  are  cut  into  pebbles,  which 
are  glazed  and  dried  like  common  powder,  but  the  drying  must 
be  slow.  For  the  prismatic  powder,  the  green  charge  is  pressed 
in  hexagonal  moulds  to  form  short  prisms,  from  f  to  If  inches  in 
diameter.  With  the  solid  prism  the  burning  surface  continually 
diminishes  as  the  combustion  progresses,  thus  decreasing  the  rapid- 
ity of  the  gas  evolution.  For  use  in  heavy  ordnance,  it  is  best  that 
the  evolution  of  gas  (i.e.  the  combustion)  shall  be  slow  at  first,  until 
the  inertia  of  the  projectile  is  overcome,  and  then  an  increas- 
ing evolution  of  gas  is  desired.  By  perforating  the  prism  with 
one  or  more  holes,  the  combustion  extends  along  the  perfora- 
tions into  the  interior,  hollowing  out  the  grain  and  continually  in- 
creasing the  burning  surface,  with  consequent  increased  evolution 
of  gas.  Thus  less  strain  is  exerted  on  the  gun,  and  greater  velocity 
imparted  to  the  ball.  Fine-grain  powders  burn  much  more  rapidly 
than  do  coarse-grain,  and  the  strain  on  the  gun  is  proportionately 
greater. 

The  United  States  army  standard  black  powder  is  composed  of  :  — 

Potassium  nitrate,  75  per  cent  by  weight. 
Carbon  (as  charcoal),  15  per  cent  by  weight. 
Sulphur,  10  per  cent  by  weight. 

The  combustion  of  this  powder  in  an  unconfined  state  may  be 
represented  as  follows  :  — 

2  KNO3  +  3  C  +  S  =  3  CO2  +  N2  +  K2S.* 

But  when  exploded  in  a  confined  space  under  pressure,  the  reaction 
becomes  very  complex,  and  many  other  substances  are  formed.  Ac- 
cording to  Debus,  f  it  is  represented  by  the  following  equation  :  — 

8  KNO3  +  9  C  +  3  S  =  2  K2CO3  +  K2SO4  +  K2S2  +  7  CO2  +  4  N2. 


According  to  Guttmann,t  some  fifteen  products  are  formed  by 
the  free  burning  of  powder,  of  which  the  chief  are  potassium  sulphate, 
potassium  carbonate,  carbon  dioxide,  nitrogen,  and  carbon  monoxide. 
The  products  .of  the  combustion  consist  of  about  57  per  cent 
solids  and  43  per  cent  gases,  by  weight.  The  pressure  exerted  by  the 

*  C.  E.  Munroe,  Rec.  U.  S.  Naval  Institute,  4,  21. 
t  Annalen  der  Chemie  und  Pharmacie,  265,  312. 
J  Industrie  der  Explosivstoffe,  p.  309. 


EXPLOSIVES  475 

• 

explosion  of  powder  entirely  filling  a  closed  space  is  about  44  tons  per 
square  inch,  or  nearly  6400  atmospheres. 

Brown  or  cocoa  powder  used  for  military  purposes,  especially  for 
heavy  guns,  has  slower  combustion  and  less  dense  smoke  than  black 
powder.  It  contains  about  the  following  ingredients  :  — 

Potassium  nitrate 79  per  cent 

Sulphur 2  to    3    " 

Carbonaceous  matter ......  18    "       " 

Moisture 0  to    1     "       " 

The  carbonaceous  matter  is  partially  charred  rye  straw,  which, 
it  is  supposed,  is  carbonized  by  exposing  it  to  superheated  steam 
until  it  takes  on  a  light  brown  (chocolate)  color.  Owing  to  incom- 
plete carbonization  of  the  straw,  the  charcoal  is  readily  combustible, 
and  can  be  used  with  a  small  proportion  of  sulphur. 

Mining  powders  of  several  grades  are  made  by  varying  the  pro- 
portion of  nitre,  sulphur,  and  charcoal,  according  as  a  quick-  or  slow- 
burning  explosive  is  desired.  These  are  generally  coarse-grained, 
and  are  cheaper  than  the  finer  rifle  powders.  Sometimes  they  are 
made  with  sodium  nitrate  instead  of  with  potassium  nitrate,  but  this 
salt  is  somewhat  hygroscopic  and  may  absorb  sufficient  moisture  to 
damage  the  powder.  Potassium  chlorate  has  been  used  instead  of 
nitre,  but  it  is  more  expensive  and  more  dangerous  in  mixing  and 
handling,  owing  to  its  sensitiveness  to  shocks.  A  white  gunpowder 
was  formerly  made  from  potassium  chlorate,  potassium  ferrocyanide, 
and  sugar.  It  possessed  no  special  advantages  over  common  black 
powder.  Barium  and  ammonium  *  nitrates  have  been  used  to  replace 
the  potassium  salt,  but  being  more  costly,  find  no  general  use.  A  so- 
called  "  amide  powder,"  made  in  Germany,  consists  of  ammonium 
nitrate  with  some  potassium  nitre.  It  forms  little  smoke  or  flame. 

Gunpowder  ignites  at  about  300°  C.,  and  the  rapidity  of  combus- 
tion increases  with  the  increase  of  pressure.  Hence  the  importance 
of  "  tamping  "  in  blasting. 

Nitrocellulose,  or  gun-cotton,  is  prepared  by  treating  cellulose 
fibre  in  a  mixture  of  concentrated  nitric  and  sulphuric  acids.  Its 
constitution  was  formerly  considered  to  be  that  of  a  true  nitro-body, 
having  the  formula,  C6H7O5  •  (NC^s,  t>ut  it  is  now  regarded  as  a 
nitrate  of  cellulose.  Eder,f  assuming  the  formula  of  cellulose  to  be 

*  Ammonium  nitrate  is  used  in  mining  powders  to  lessen  the  flame  and  high 
temperature  of  the  explosion.  Such  powders  are  used  in  mines  where  fire-damp 
occurs. 

t  Zeitschr.  f.  angew.  Chemie,  1901. 


476  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


,  concluded  that  the  highest  degree  of  nitration  was  found  in 
the  hexanitrate  and  proposed  Ci2Hi4O4  •  (NO3)e  as  the  formula  for 
gun-cotton,  and  that  the  formation  took  place  thus  :  — 

Ci2H2oO5  +  6  HN03  =  Ci2H14O4  •  (NO3)6  +  6  H2O.* 

The  decomposition  on  explosion  is  represented  thus  :  — 
Ci2Hi4O4  •  (NO3)6  =  7  CO2  +  5  CO  +  3  N2  +  3  H2O  +  4  H2. 

Vieille  f  found  eight  different  types  of  nitrocellulose,  and  proposed 
C^HtoC^o  as  the  cellulose  formula  ;  his  highest  nitration  product  con- 
tained 13.47  per  cent  of  nitrogen  corresponding  to  the  formula 
C24H2909  -  (N08)u. 

The  amount  of  gas  set  free  from  one  kilogram  of  gun-cotton  is 
982  litres  (water  as  vapor)  and  the  heat  liberated  is  1074  Cals.  ;  J  the 
temperature  of  the  explosion  has  been  estimated  as  6000°  C. 

Gun-cotton  was  discovered  by  Schoenbein  in  1846,  and  attempts 
were  made  in  several  countries  to  use  it  for  military  purposes.  But 
several  spontaneous  explosions  of  magazines  occurred,  which  soon 
caused  it  to  be  given  up.  Von  Lenk  in  1849-1853  proved  these  ex- 
plosions to  be  due  to  incomplete  conversion  in  the  nitration  and  the 
presence  of  free  acid,  left  within  the  fibre.  Cotton  fibre  is  a  long, 
hollow  tube,  much  twisted  and  shrunken,  into  which  the  acid  pene- 
trates and  is  only  removed  with  great  difficulty,  unless  the  fibre  is 
cut  and  ground  to  a  fine  pulp.  In  1865  Abel  improved  the  process 
of  manufacture  by  pulping  and  compressing  the  gun-cotton,  and  now, 
when  properly  made,  it  is  considered  one  of  the  safest  of  explosives. 

The  cotton  used  §  is  the  short  fibre  ("  linters  "II)  removed  from  the 
seed  husk  after  ginning,  which  has  been  carefully  purified  from  the 
grease,  dirt,  and  natural  oil  by  a  long  "  soda  boil  "  (p.  505)  followed 
by  washing  in  hot  water.  After  drying,  the  cotton  is  run  through  a 
"picker  machine,"  to  loosen  the  fibres,  and  then  dried  at  225°  F. 
until  the  moisture  is  less  than  0.5  per  cent.  It  is  then  placed  in  sealed 
cans  to  cool.  The  nitration  is  effected  with  a  cold  mixture  of  3  parts 
of  pure  sulphuric  acid  of  sp.  gr.  1.842,  and  1  part  of  pure  nitric  acid 
of  sp.  gr.  1.52.  The  nitrating  may  be  done  in  a  cast-iron  tank 
(dipping  pot)  cooled  by  a  water-jacket.  The  apparatus  will  hold 

*  Guttmann,  Industrie  der  Explosivstoffe,  318. 
t  Moniteur  scientifique,  1897. 
j  Berthelot. 

§  Met.  Chem.  Eng.  1915  (XIII),  361. 

||  For  some  purposes  wood  pulp,  or  pure  tissue  paper  especially  prepared,  may 
be  used  for  nitration  instead  of  cotton, 


EXPLOSIVES  477 

from  120  to  250  Ibs.  of  mixed  acid,  and  about  2  Ibs.  of  cotton  (intro- 
duced in  several  small  portions)  are  treated  at  one  time.  Each  por- 
tion of  cotton  as  introduced  is  quickly  submerged  in  the  acid  by 
means  of  an  iron  or  aluminum  fork.  After  soaking  15  to  30  minutes, 
the  cotton  is  raked  out  of  the- acid  and  drained  on  an  iron  grid,  against 
which  it  is  pressed  by  an  iron  plate  connected  with  a  lever,  the  excess 
acid  flowing  back  to  the  tank.  The  cotton  absorbs  about  10  to  11 
times  its  weight  of  acid,  and  this  amount  of  fresh  acid  mixture  is  added 
to  the  tank  before  the  next  dipping.  The  gun-cotton  is  transferred 
to  a  centrifugal  machine  having  a  steel  or  earthenware  basket  and 
whizzed  for  a  few  minutes  to  remove  as  much  acid  as  possible.  The 
gun-cotton  is  then  removed  from  the  centrifuge,  in  small  quantities 
at  one  time,  with  steel  forks,  and  quickly  plunged  into  a  large  vat 
full  of  cold  water,  and  well  stirred  to  dissipate  the  acid  and  keep  down 
the  temperature.  Very  often  this  washing  is  carried  on  in  a  hollander 
machine  (p.  559),  the  drum  of  which  is  furnished  with  beaters  instead 
of  knives.  When  the  cotton  is  no  longer  acid  to  litmus,  it  is  boiled 
for  about  48  hours,  in  wooden  vats,  heated  by  steam  coils ;  the  coils 
are  surrounded  by  fine  wire  gauze,  to  prevent  the  gun-cotton  from 
touching  the  hot  pipes.  The  water  is  changed  several  times  during 
the  boiling,  but  the  gun-cotton  persistently  retains  traces  of  acid. 
To  remove  this  acid  the  fibre  is  then  pulped  in  hollanders  having  drums 
set  with  knives,  as  for  paper  making  (p.  560).  Often  a  little  calcium 
carbonate  is  added  towards  the  end  of  the  pulping,  to  neutralize  any 
remaining  traces  of  acid.  The  pulp  is  then  separated  from  the  excess 
water  in  cloth-lined  centrifugals,  or  in  drainer  vats  having  cloth  laid 
on  the  perforated  bottom.  The  wet  pulp  is  then  pressed  to  reduce 
the  water  content  to  the  desired  degree  and  to  increase  the  density 
of  the  pulp.  Well-made  gun-cotton  should  not  contain  much  more 
than  4  per  cent  of  collodion  cotton  (soluble  in  alcohol-ether  mixture). 

For  military  purposes  the  gun-cotton  pulp  is  compressed  very 
heavily  to  form  cakes  of  suitable  size  and  shape  for  charging  torpedoes 
and  mines.  The  moist  gun-cotton  is  safer  to  handle  and  transport, 
but  will  explode  by  detonation  with  a  mercury  fulminate  cap.  To 
prevent  loss  of  the  moisture,  the  blocks  after  compression  may  be 
coated  with  paraffine  wax,  or  varnished  with  an  acetone  or  ethyl 
acetate  solution  of  nitrocellulose,  which  forms  an  impervious  film; 
they  are  then  enclosed  in  zinc  or  metal  canisters. 

Nitration  in  centrifugal  machines  is  commonly  practised  and  is 
more  rapid  and  convenient  than  the  use  of  dipping  tanks  and  pots. 
An  ordinary  iron  centrifugal  is  so  constructed  that  the  outlet  pipe 


478  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

may  be  closed  and  the  casing  filled  with  mixed  acid,  submerging  the 
perforated  basket.  A  cover  is  provided  with  a  large  pipe,  through 
which  the  fumes  pass  to  the  draught  flue  and  fan.  The  perfectly 
dry  cotton  is  introduced  in  single  handfuls  and  worked  into  the  acid 
with  an  iron  prong  or  bar,  while  the  basket  is  slowly  rotated.  When 
from  12  to  20  pounds  of  cotton  have  been  introduced,  the  apparatus 
stands  half  an  hour  or  more  until  nitration  is  completed.  Then  the 
outlet  pipe  is  opened,  the  acid  drawn  off,  and  the  basket  set  in  rapid 
rotation,  until  the  cotton  is  free  from  adhering  acid.  The  gun-cotton 
is  then  quickly  removed  from  the  basket  in  small  masses,  by  a  pair 
of  tongs,  and  at  once  submerged  in  a  large  tank  of  water.  The  sub- 
sequent washing  and  pulping  of  the  gun-cotton  are  essentially  as  de- 
scribed on  p.  477. 

If  a  drop  of  water  or  oil  falls  into  the  gun-cotton  in  the  centrifu- 
gal, decomposition  of  the  whole  mass  ensues,  with  copious  evolution 
of  nitrous  fumes,  but  as  a  rule  there  is  no  explosion,  and  only  the  loss 
of  the  cotton  results. 

Nitration  by  the  displacement  process  of  Thomson  has  been  sub- 
stituted for  the  centrifugal  and  dipping  methods  in  some  works.  In 
this  are  used  earthenware  vessels,  having  a  perforated  false  bottom, 
and  a  drain-cock  below,  through  which  the  mixed  acid  is  introduced 
into  the  vessel,  and  also  drawn  off  at  the  end  of  the  nitration.  The 
vessel  is  covered  with  an  aluminum  hood  from  which  the  fumes  evolved 
are  drawn  away  by  suction.  The  cotton  is  introduced  in  small  por- 
tions until  about  20  Ibs.  are  in  the  apparatus  and  is  left  in  the  acid  for 
two  or  more  hours ;  a  perforated  iron  or  aluminum  plate  is  then  laid 
on  top  of  the  cotton,  compressing  it  slightly,  and  finally  water  is  run 
over  the  perforated  plate  in  a  slow  stream,  while  the  drain-cock  is 
cautiously  opened  to  allow  the  mixed  acid  to  escape  slowly  at  a  rate 
corresponding  to  the  inflow  of  water  above  the  plate.  Thus  little 
diffusion  of  water  into  the  acid  takes  place,  and  most  of  the  acid  is 
drawn  off  in  a  concentrated  state  suitable  for  re-inforcing  with  more 
strong  acid.  The  temperature  is  also  kept  low,  and  there  is  less  risk 
of  decomposing  the  nitrated  cotton.  The  washing  and  pulping  of 
the  cotton  are  similar  to  the  previous  processes. 

Well-made  gun-cotton  is  insoluble  in  water,  alcohol,  ether,  and 
chloroform.  It  is  somewhat  soluble  in  acetone  and  in  ethyl  acetate, 
and  swells  to  form  a  jelly-like  mass  with  nitrobenzene.  It  resembles 
the  original  cotton  in  appearance,  but  is  slightly  harsher  to  the  touch. 
It  is  not  exploded  readily  by  shocks,  but  explodes  with  great  violence 
when  detonated.  When  unconfined,  it  burns  rapidly  with  a  large 


EXPLOSIVES  479 

'flame.     When  not  washed  entirely  free  from  acid,  it  is  liable  to  spon- 
taneous decomposition  and  explosion. 

Lower  cellulose  nitrates  are  prepared  as  collodion-cotton  or  pyroxy- 
line,  for  making  smokeless  powder,  gelatine  dynamite,  blasting  gela- 
tine, etc.  These  collodion-cottons  also  enter  into  the  composition  of 
celluloid  and  various  other  plastics,  photographic  films,  artificial 
silk,  waterproof  varnishes,  and  surgical  dressings.  Collodion-cotton 
is  readily  soluble  in  alcohol-ether  mixture,  and  is  made  by  immersing 
the  cotton  for  one  or  two  hours  in  a  mixture  of  concentrated  sul- 
phuric acid  with  nitric  acid  of  1.45  sp.  gr.  The  strength  of  the  acid 
and  the  temperature  and  time  of  nitration  influence  the  solubility  of 
the  collodion  considerably. 

Nitroglycerine,  C3H5(NO3)3,  was  discovered  in  1847,  but  no  at- 
tempt to  make  practical  use  of  it  was  made  until  about  1864,  when 
Nobel  established  a  factory  and  began  its  production  on  a  large  scale. 
But  very  soon  a  number  of  explosions  occurred  when  handling  and 
transporting  the  liquid,  and  means  were  at  once  sought  to  render  it 
less  dangerous.  In  1866  Nobel  invented  dynamite,  by  absorbing  the 
liquid  nitroglycerine  in  diatomaceous  earth,  and  this  is  now  the  form 
in  which  most  nitroglycerine  is  utilized. 

The  name  nitroglycerine  is  a  misnomer  which  was  given  under 
the  erroneous  supposition  that  it  contained  the  nitro  group  NO2,  but 
its  true  constitution  was  later  shown  to  be  glyceryl  trinitrate.  It  is 
easily  made  by  the  action  of  concentrated  nitric  acid  on  glycerine :  — 

C3H5(OH)3  +  3  HNO3  =  3  H2O  +  C3H5(NO3)3. 

A  mixture  of  250  parts  of  nitric  acid  (98  per  cent  HNO3)  with  350 
parts  of  sulphuric  acid  (96  per  cent  H2SO4)  is  used  for  each  100  parts 
of  glycerine  (sp.  gr.  1.262,  see  p.  385).  Nitroglycerine  is  somewhat 
soluble  in  both  nitric  and  sulphuric  acids,  but  is  not  dissolved  by  the 
mixture ;  hence,  better  separation  is  obtained  after  the  nitration.  The 
nitrating  vessel  is  an  iron  or  lead-lined,  water-jacketed,  covered  tank, 
containing  lead  coils  through  which  cold  water  is  circulated.  A 
rotating  stirrer,  or  perforated  pipe  through  which  cold,  dry  air  can 
be  introduced,  serves  to  keep  the  mixture  agitated  during  nitration. 
In  the  bottom  of  the  tank  are  large  taps,  leading  to  a  vat  beneath, 
containing  a  large  volume  of  cold  water.  In  case  of  dangerous  rise 
of  temperature  during  nitration,  the  entire  charge  can  be  quickly 
emptied  into  this  "  drowning  tank,"  which  stops  further  action. 

The  entire  amount  of  mixed  acid  is  put  in  the  nitrator,  and  glyc- 


480  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

erine  (at  20°  to  25°  C.)  added  in  numerous  fine  streams  from  a  per-* 
forated  pipe,  or  sprayed  in  by  an  air-blown  injector.  The  tank  is 
covered,  and  a  pipe  carries  away  the  fumes.  The  temperature  *  of 
the  reaction,  as  shown  by  thermometers,  must  not  rise  above  30°  C. ; 
it  is  regulated  by  the  rate  of  inflow  of  the  glycerine,  and  by  compressed 
air  agitators  or  mechanical  paddle  stirrers.  After  the  reaction  is 
over,  the  entire  charge  is  run  into  a  separator  tank,  where  it  stands 
until  the  nitroglycerine,  being  lighter  than  the  acid,  all  rises  to  the 
top.  It  is  drawn  off  by  an  adjustable  skimmer,  which  delivers  it 
into  a  tank  of  water  that  is  not  colder  than  15°  C.,  lest  the  nitro- 
glycerine freeze.  The  product  is  washed  several  times  with  water, 
and  then  with  dilute  sodium  carbonate  solution,  to  remove  all  traces 
of  acid.  The  yield  from  100  Ibs.  of  glycerine  is  about  220  Ibs.  of 
product.  Single  charges  of  2500  Ibs.  or  more  of  glycerine  are  often 
nitrated  in  this  way.  The  spent  acids,  further  separated  from  any 
traces  of  nitroglycerine  by  standing  a  day  or  two,  are  then  denitrated 
by  treating  with  steam  and  air,  or  they  may  be  used  in  the  nitric  acid 
retorts  with  sodium  nitrate.  Sometimes  they  are  "  revivified,"  by 
adding  the  required  amounts  of  fuming  sulphuric  and  nitric  acids. 
On  explosion,  nitroglycerine  decomposes  about  as  follows :  — 

2  C3H5(NO3)3  =  6  CO2  +  3  N2  +  5  H2O  +  i  O2. 

The  volume  of  gas  at  100°  C.  thus  produced  is  about  six  times  as 
great  as  from  gunpowder,  and  the  actual  temperature  of  the  explo- 
sion is  much  higher  than  that  of  gunpowder,  being  about  3000°  C.  as 
calculated  by  Wuic  (quoted  by  Guttmann).  The  volume  of  gas  pro- 
duced by  one  liter  of  nitroglycerine  is  about  1135  liters.  According 
to  Ost,f  the  temperature  of  the  explosion,  as  calculated  from  the 
observed  heat  of  the  explosion  and  the  specific  heat  of  the  products 
of  the  combustion,  is  6980°  C.  This  temperature  is  probably  too 
high,  due  to  the  use  of  low  values  for  the  specific  heats  of  the  gases 
and  to  disregard  of  the  dissociation  at  high  temperatures.  Neglect- 
ing these  factors,  the  pressure  developed  would  be  about  31,400  kilo- 
grams per  square  centimeter. 

*  For  better  control  of  the  process,  Boutmy  and  Faucher  mix  the  glycerine  with 
part  of  the  sulphuric  acid,  and  cool  the  resulting  sulphoglyceric  acid,  CsHXOH):  • 
(HSCh),  or  CsHXHSO^s.  The  nitric  acid  is  mixed  with  the  rest  of  the  sulphuric, 
and  after  cooling,  the  sulphoglyceric  acid  is  added ;  nitroglycerine  is  thus  formed 
with  much  less  heat  evolved  than  when  nitrating  the  glycerine  directly.  When 
using  this  process,  several  explosions  occurred  which  were  difficult  to  explain,  and 
it  has  been  generally  abandoned. 

t  Lehrbuch  der  technischen  Chemie,  5te  Auf.,  182. 


EXPLOSIVES  481 

Nitroglycerine  is  a  heavy  oily  liquid  of  a  pale  yellow  color  and 
sweet  taste.  Its  specific  gravity  is  1.60.  It  is  insoluble  in  water,  but 
dissolves  in  ether,  benzene,  methyl  alcohol,  and  chloroform.  It  freezes 
at  about  8°  C.  and  thaws  at  about  12°  C.,  though  there  is  some  varia- 
tion in  these  points  in  different  samples,  according  to  their  purity. 
It  explodes  when  heated  to  180°  CL  but  burns  in  the  open  air  without 
explosion,  if  in  small  quantities.  It  is  very  sensitive  to  shocks  and 
may  readily  be  detonated  by  a  sharp  blow.  This  sensitiveness  is 
reduced  by  the  addition  of  nitro-naphthalenes,  and  these  are  also 
claimed  to  prevent  the  freezing  of  dynamite.*  When  pure,  it  keeps 
indefinitely  in  a  dark  place,  but  exposure  to  sunlight  increases  its  sen- 
sitiveness and  may  cause  spontaneous  explosion.  Taken  internally, 
it  is  very  poisonous  and  is  a  powerful  medicinal  agent,  somewhat 
resembling  strychnine  in  its  physiological  effects ;  ten  grains  are  said  to 
be  a  fatal  dose,  while  smaller  quantities  cause  headache  and  vertigo ; 
even  when  only  in  contact  with  the  skin,  it  13  said  to  cause  violent 
headache.  It  is  used  as  a  remedy  in  angina  pectoris,  and  is  injected 
into  the  blood  in  cases  of  poisoning  by  carbon  monoxide,  or  water-gas. 

As  an  explosive,  it  is  only  used  in  the  liquid  state  for  "  torpe- 
doing "  oil  and  gas  wells  (p.  338).  When  frozen,  it  is  much  less  sen- 
sitive to  shocks,  and  may  be  transported  and  handled  with  safety. 
But  before  use,  it  should  be  thawed  by  standing  in  a  room  warmed 
to  about  20°  C.  It  is  one  of  the  ingredients  of  a  large  number  of 
high  explosives  which,  although  not  so  powerful  as  the  nitroglycerine 
itself,  are  much  safer  and  more  convenient  to  handle.  These  ex- 
plosives may  be  divided  into  two  classes :  (a)  those  in  which  the 
nitroglycerine  is  absorbed  in  some  inert,  non-explosive  material,  and 
(b)  those  in  which  it  is  mixed  or  combined  with  substances  which  are 
in  themselves  explosive.  The  most  important  example  of  the  first 
class  is  dynamite ;  in  this  the  nitroglycerine  is  absorbed  in  infusorial 
earth,  white  clay,  pulverized  mica,  wood  pulp,  sawdust,  or  powdered 
charcoal.  The  chief  requisite  of  a  good  absorbent  or  "  dope  "  is  that 
it  shall  hold  the  nitroglycerine  without  any  oozing  or  dripping,  other- 
wise the  liquid  spreads  in  thin  films  over  the  outside  of  the  package, 
and  becomes  extremely  sensitive  to  shocks,  and  very  dangerous. 
Infusorial  earth,  often  known  by  its  German  name,  Kieselguhr,  is 
much  used  in  Europe  as  an  absorbent.  It  is  a  white  clay,  containing 
a  large  amount  of  the  frustules  of  diatoms,  which  are  chiefly  minute 
tubes,  into  which  the  nitroglycerine  is  drawn  by  capillary  attraction, 
and  permanently  held.  The  kieselguhr  is  calcined  to  dry  it,  and  to 

*  J.  Soc.  Chem.  Ind.,  1897,  933. 
2i 


482 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


destroy  organic  matter,  and  is  then  mixed  by  hand  with  the  requisite 
amount  of  nitroglycerine  and  a  little  calcined  soda,  to  destroy  any 
acidity.  With  three  parts  of  nitroglycerine  to  one  of  kieselguhr,  the 
dynamite  is  plastic,  and  contains  75  per  cent  of  its  weight  of  nitro- 
glycerine. In  America,  wood  pulp  to  which  some  sodium  nitrate  is 
added  is  commonly  used  as  "  dope."  This  will  absorb  about  75  per 
cent  of  nitroglycerine,  and  forms  the  dynamite  No.  i,  or  giant  powder. 
Weaker  dynamite  with  60,  40,  or  20  per  cent  nitroglycerine  is  pre- 
pared for  use  where  the  No.  1  grade  would  cause  too  much  shatter- 
ing. Dynamite  is  packed  into  tubes  of  paraffined  paper,  and  com- 
pressed by  hand  to  form  cartridges  of  convenient  weight.  It  is  not 
very  sensitive  to  shocks,  but  is  readily  detonated  by  an  explosive 
cap.  In  cold  weather  the  nitroglycerine  congeals,  and  such  frozen 
dynamite  does  not  give  good  results.  It  is  best  thawed  by  placing 
in  a  warm  room  for  some  time  before  use.  Special  water-jacketed 
warming  pans  are  also  used  for  thawing  dynamite.  It  should  never 
be  heated  over  a  stove  or  fire,  as  prolonged  heating  to  70°  or  80°  C. 
has  caused  explosions. 


Most  of  the  nitroglycerine  explosives  employed  contain  an  active 
dope  such  as  mixtures  of  sulphur,  with  sodium,  potassium,  or  am- 
monium nitrate  and  powdered  charcoal,  wood  fibre,  or  other  carbo- 
naceous matter.  Examples  of  these  are  the  various  brands  called 
Atlas,  Forcite,  Hecla,  Hercules,  Judson,  and  Vulcan  powders,  and 
carbonite,  lithofracteur,  stonite,  vigorite,  etc.  The  ammonium 
nitrate  powders  are  much  used  in  coal  mining,  where  gas  or  dust  ex- 
plosions may  follow  a  blast.  Ammonium  nitrate  may  be  detonated, 
and  as  the  temperature  of  its  explosion  is  low  (about  1100°  to  1200° 
C.)  it  produces  little  flame,  while  absorbing  some  heat  from  the  gases 
produced  by  the  explosive  with  which  it  is  mixed.  Such  powders 
containing  ammonium  nitrate,  or  salts  with  water  of  crystallization 
(Epsom  salts,  etc.),  are  often  called  "  safety  explosives.'' 

As  typical  examples  of  these  explosives,  the  following  will  serve  :  — 


ATLAS  POWDER 

JUDSON  POWDER 

FORCITE 

Grade  A 

Grade  B 

Sodium  nitrate  .     . 

2 

34 

Sodium  nitrate  .     . 

64 

Potassium  nitrate  . 

18 

Wood  fibre     .     .     . 

21 

14 

Sulphur    .... 

16 

Gelatinized  cotton 

7 

Magnesium    carbo- 

Cannel coal  .     .     . 

15 

Nitroglycerine  .     . 

75 

nate  
Nitroglycerine    .     . 

2 

75 

2 

50 

Nitroglycerine  .     . 

5 

EXPLOSIVES  483 

Forcite  is  a  plastic  mass,  resembling  rubber,  impervious  to  water, 
and  safe  to  handle.  It  is  made  by  treating  finely  pulped  cotton  with 
high-pressure  steam  until  the  whole  mass  is  converted  into  a  jelly, 
which  is  then  mixed  with  nitroglycerine  at  a  temperature  of  40°  C., 
and  powdered  nitre  is  then  added. 

Nitrogelatine  or  blasting  gelatine  is  made  by  dissolving  soluble 
nitrated  cellulose  (collodion)  in  nitroglycerine.  The  latter  is  warmed 
to  about  35°  C.,  and  the  collodion  slowly  stirred  in,  until  7  or  8  per 
cent  has  been  added.  After  a  time  the  mass  becomes  viscous,  and  is 
formed  into  cartridges.  It  is  not  very  sensitive  to  shocks,  and  may 
be  made  less  so  by  adding  3  or  4  per  cent  of  camphor.  It  is  not 
affected  by  water  and  hence  may  be  used  for  submarine  work.  It 
keeps  well  when  stored,  and  is  a  more  powerful  explosive  than 
dynamite. 

Gelatine  dynamite  consists  of  blasting  gelatine,  mixed  with  wood 
pulp  (4J  per  cent)  and  potassium  nitrate  (26  per  cent),  together  with 
a  little  sodium  carbonate. 

An  explosive  somewhat  similar  to  blasting  gelatine  is  cordite,  a 
"  smokeless  powder,"  which  has  been  adopted  by  the  English  gov- 
ernment as  a  military  explosive.  This  was  patented  by  Abel  and 
Dewar,  and  consists  of :  — 

Nitroglycerine 58     parts. 

Gun-cotton 37         " 

Vaseline .       5         " 

Acetone 19.2      " 

The  nitroglycerine  and  gun-cotton  are  mixed  by  hand,  the  ace- 
tone is  added,  and  the  paste  worked  in  a  kneading  machine  for  3j 
hours.  The  vaseline  is  then  added,  and  the  whole  kneaded  for  3 
hours  more.  The  paste  is  then  forced  through  a  spaghetti  machine 
to  form  threads,  which  are  wound  on  drums  and  dried  at  40°  C.  for 
several  days  to  evaporate  off  the  acetone.  The  threads  are  then  cut 
into  convenient  lengths  for  use  in  cartridges. 

Smokeless  powders  are  important  for  military  and  sporting 
purposes.  They  are  probably  too  expensive  for  blasting  and  mining. 
The  base  of  these  powders  is  nitrated  cellulose,  which  has  been 
treated  in  various  ways  to  render  it  slower  in  burning  than  gun- 
cotton,  and  also  less  sensitive  to  heat  and  shocks.  As  a  rule,  they 
are  less  inflammable  than  gun-cotton,  and  require  stronger  deto- 
nators. Since  metallic  salts  cause  smoke,  they  are  not  used  in  these 
powders.  There  are  three  general  classes  of  smokeless  powders  now 
in  use :  (a)  Those  consisting  of  mixtures  of  nitroglycerine  and  nitrated 


484  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

cellulose,  which  have  been  converted  into  a  hard,  horn-like  mass, 
either  with  or  without  the  aid  of  a  solvent.  To  this  group  belongs 
baUistite,  containing  50  per  cent  nitroglycerine,  49  per  cent  nitrated 
cellulose  (collodion),  and  1  per  cent  diphenylamine ;  *  also,  cordite 
(see  above),  Leonard's  powder,  and  amberite.  This  last  contains  40 
parts  nitroglycerine  and  56  parts  nitrated  cellulose.  (6)  Those  con- 
sisting mainly  of  nitrated  cellulose  of  any  kind,  which  has  been 
rendered  hard  and  horny  by  treatment  with  some  solvent,  which  is 
afterwards  evaporated.  These  are  prepared  by  treating  nitrated 
cellulose  with  ether  or  benzene,  which  dissolves  the  collodion,  and 
when  evaporated  leaves  a  hard  film  of  collodion  on  the  surface  of 
each  grain.  Sometimes  a  little  camphor  is  added  to  the  solvent,  and, 
remaining  in  the  powder,  greatly  retards  its  combustion,  (c)  Those 
consisting  of  nitro-derivatives  of  the  aromatic  hydrocarbons,  either 
with  or  without  the  admixture  of  nitrated  cellulose;  to  this  group 
belong  Dupont's  powder,  consisting  of  nitrated  cellulose  dissolved  in 
nitrobenzene ;  indurite,  consisting  of  cellulose  hexanitrate  (freed  from 
collodion  by  extraction  with  methyl  alcohol)  made  into  a  paste  with 
nitrobenzene,  and  hardened  by  treatment  with  steam  until  the  excess 
of  nitrobenzene  is  removed ;  and  plastomenite,  consisting  of  dinitro- 
toluene  and  nitrated  wood  pulp. 

Another  class  of  explosives  which  are  not,  however,  much 
employed  are  the  picrates  and  picric  acid.  By  treating  phenol, 
CeHe  •  OH,  with  concentrated  nitric  acid,  tri-nitrophenol  or  picric 
acid,  C6H2(OH)  •  (NO2)3,  is  formed.  The  alkaline  salts  of  this  body 
(called  picrates)  are  powerful  explosives,  but  are  too  dangerous  for  use. 

The  salts  of  fulminic  acid,  C2H2O2N2,  called  fulminates,  are  ex- 
ceedingly dangerous,  being  easily  exploded  by  shocks  or  blows. 
The  silver  and  mercury  fulminates  are  the  most  important.  The 
former  is  too  dangerous  for  general  use,  but  the  latter  is  largely  used 
as  the  "primer  "  in  percussion  caps.  It  is  made  by  mixing  a  solution 
of  mercuric  nitrate  and  nitric  acid  with  alcohol.  It  is  a  very  danger- 
ous explosive  when  dry. 

Lead  azide  and  other  heavy  metal  salts  of  hydrazoic  acid  (NaH) 
also  find  use  as  detonators,  being  stronger  than  the  fulminates. 

In  order  to  avoid  danger  in  shipping  and  handling,  a  class  of  ex- 
plosives has  come  into  use  in  which  the  ingredients,  in  themselves 

*  Nitroexplosives  tend  to  decompose  slowly  with  evolution  of  nitrous  acid  ;  the 
acidity  renders  the  explosive  unstable.  The  diphenylamine  serves  to  eliminate  the 
nitrous  acid  as  soon  as  formed. 


EXPLOSIVES  485 

non-explosive,  are  mixed  immediately  before  use.  These  are  called 
Sprengel  explosives,  from  the  name  of  the  inventor;  they  are  very 
powerful  in  many  cases,  and  some  of  them  are  extensively  used. 
Roburite  consists  of  dinitrochlorbenzene,  or  possibly  dinitrobenzene 
alone,  mixed  with  ammonium  nitrate.  It  does  not  explode  by  fric- 
tion or  shock,  but  is  readily  detonated.  It  yields  hydrochloric  acid 
in  the  combustion  gases,  and  hence  is  disadvantageous  in  mining. 
Bellite  and  securite  are  somewhat  similar  to  roburite.  Romite  con- 
tains nitronaphthalene,  paraffine,  potassium  chlorate,  and  ammonium 
nitrate,  in  various  proportions.  Ammonite  contains  nitronaphthalenes 
and  ammonium  nitrate.  Rack-a-rock  is  made  from  potassium  chlo- 
rate soaked  in  nitrobenzene,  or  in  the  "  dead  oil  "  from  tar.  It  is 
very  powerful,  and  moderate  in  price.  It  was  largely  used  in  the 
removal  of  Hell  Gate  in  New  York  Harbor.  Panclastite  is  a  liquid 
consisting  of  carbon  disulphide  with  liquid  nitrogen  peroxide.  Hell- 
hoffite  consists  of  nitro-  and  dinitro-benzenes  dissolved  in  nitric  acid. 

Military  explosives  must  be  very  stable  against  accidental  shock. 
They  comprise  two  classes,  the  propellants  or  explosives  used  in  guns 
to  drive  the  projectile,  and  high  explosives  used  for  shells,  torpedoes, 
etc.  The  latter  must  be  sufficiently  stable  against  shock  to  be  un- 
affected by  the  discharge  of  the  gun,  but  capable  of  explosion  by 
detonation.  The  basis  of  most  propellants  is  nitrocellulose,  the  speed 
of  explosion  of  which  is  controlled  by  the  admixture  of  modifying 
substances,  and  by  the  shape  and  density  of  the  grain,  e.  g.  smokeless 
powders,  p.  484.  For  shells  the  chief  substances  are  picric  acid  and 
trinitrotoluol  (TNT);  the  latter  especially  is  stable  to  all  influences 
except  detonation  and  has  the  advantage  of  high  density. 

Melinite  is  a  mixture  of  picric  acid  with  collodion,  or  in  one  form 
is  supposed  to  be  fused  picric  acid  alone,  which  has  been  melted  in  a 
carefully  regulated  oil-bath.  It  is  used  in  France  for  a  military 
explosive  for  shells,  by  the  English  Government  as  lyddite,  and  by 
the  Japanese  under  the  name  "  shimose." 

In  coal  mines,  especially  where  "  fire  damp"  is  prevalent,  lime 
cartridges  are  sometimes  used.  These  are  made  by  compressing 
quicklime  into  cylinders,  leaving  a  small  hole  down  the  middle. 
They  are  put  into  drill  holes,  and  tamped  with  sand.  Water  is 
poured  into  the  hole,  and,  passing  into  the  perforated  cylinder,  wets 
the  lime,  which  swells  greatly  on  slaking,  and  exerts  great  pressure. 
The  coal  is  broken  down  without  any  flame  or  concussion,  and  hence 
there  is  no  danger  from  the  gas. 


486  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

REFERENCES 

Tri-Nitroglycerine  as  applied  in  the  Hoosac  Tunnel.     Geo.  M.  Mowbray, 

New  York,  1874.     (Van  Nostrand.) 

Notes  on  Certain  Explosive  Agents.     Walter  N.  Hill,  Boston,  1875. 
Researches  in  Explosives.     Captain  Noble  and  F.  A.  Abel. 

Part  I.     London,  1875.     Part  II.     London,  1880. 
Dynamite,  ihre  okonomische  Bedeutung  und  ihre  Gefahrlichkeit.     Isador 

Trauzl,  Wien,  1876. 

Coton-poudre,  nitroglycerine  et  dynamites.     M.  Pellet,  Paris,  1881. 
Zur  la  Force   des  Matieres   explosives   d'apres  la   Thermochimie.     M. 

Berthelot.     2  vols.     Paris,  1883. 
Die  neuen  Sprengstoffe.     Isador  Trauzl,  Wien,  1885. 
Les  Explosifs  modernes.     Paul  F.  Chalons,  Paris,  1886. 
Manuel  du  Dynamiteur.     La  Dynamite  de  Guerre  et  le  Coton-poudre. 

M.  Dumas-Giulin,  Paris,  1887. 

A  Dictionary  of  Explosives.     J.  P.  Cundill,  London,  1889. 
Die  gepresste  SchiesswoUe.     Franz  Plach,  Pola,  1891.     (E.  Scharff.) 
Explosives  and  Ordnance  Material,  etc.     Stephen  H.  Emmons.     Reprint 

from  Vol.  17,  Proc.  U.  S.  Naval  Institute,  Baltimore,  1891. 
The  Dangers  in  the  Manufacture  of  Explosives.     Oscar  Guttmann,  Lon- 
don, 1892. 

Blasting.     Oscar  Guttmann,  London,  1892. 

Les  Explosifs  industriels.     J.  Daniel,  Paris,  1893.     (Bernard  et  Cie.) 
Index  to  the  Literature  of  Explosives.     Chas.  E.  Munroe,  Baltimore,  1893. 
Die  Industrie  der  Explosivstoffe.     Oscar  Guttmann,  Braunschweig,  1895. 
Die  Explosiven  Stoffe.     Franz  Boeckmann.     2te  Auf.     Wien,  1895. 
Nitro-Explosives.     P.  Gerald  Sanford,  London,  1896.     (Lockwood.) 
A  Handbook  on  Modern  Explosives.     M.  Eissler,  London,  1897. 
Smokeless  Powder,  Nitro-Cellulose,  etc.    J.  B.  Bernardou,  New  York,  1901. 
Lectures  on  Explosives.     W.  Walke,  3d  ed.,  New  York,  1902. 
The  Manufacture  of  Explosives.     O.  Guttmann.     2  vols.  London. 
Military  Explosives.    E.  M.  Weaver,  New  York,  1906. 
Nitro-explosives.    P.  G.  Sanford,  London,  1906. 
Die  Explosivstoffe.    R.  Escales,  1908. 

Nitrocellulose  Industry.     2  vols.     E.  C.  Worden,  New  York,  1911. 
Journal  of  the  Society  of  Chemical  Industry :  — 

1890,  265.     1890,  476.     McRoberts.     Blasting  Gelatine. 
1893,  1056.     Sanford.     Nitroglycerine. 
1895,  507.     Blomen.     Nitroglycerine. 


TEXTILE  INDUSTRIES 

FIBRES 

Textile  fibres  are  divided,  according  to  their  source,  into  vege- 
table, animal,  and  mineral.  Of  these  only  the  first  two  will  be  con- 
sidered here,  since  mineral  fibres,  consisting  of  asbestos,  slag-wool, 
glass-wool,  metallic  wires,  etc.,  are  never  subjected  to  any  of  the 
processes  of  bleaching,  dyeing,  or  chemical  treatment  which  come 
within  the  scope  of  this  book,  though  they  are  sometimes  used  for 
packing,  lagging,  or  filtering  purposes  in  chemical  works. 

Vegetable  fibres  are  plant  cells  of  rather  simple  structure,  usually 
forming  a  part  of  the  plant  itself.  They  are  capable  of  withstanding 
high  heat,  and  are  not  readily  attacked  by  dilute  alkalies  to  cause 
disintegration  or  weakening.  They  consist  essentially  of  cellulose 
(CeHioOs),,,  which  may  be  pure,  or  mixed  with  its  alteration  products ; 
in  a  few  instances,  the  fibre  as  actually  employed  consists  entirely  of 
cellulose  derivatives  obtained  by  chemical  means.  Concentrated 
caustic  alkalies  form  alteration  products  with  vegetable  fibre ;  free 
sulphuric,  or  hydrochloric  acid,  if  strong,  quickly  destroys  the  fibre, 
but  nitric  acid  forms  nitrates,  or  oxidized  derivatives. 

Animal  fibres  are  essentially  nitrogenous  substances  (protein 
matter)  often  containing  sulphur.  They  may  consist  of  complex  cell 
structures,  or  bundles  of  cells  enclosed  in  a  single  envelope,  or  they 
are  solid  filaments  formed  from  a  liquid  secreted  by  caterpillars, 
spiders,  or  certain  mollusks.  They  are  readily  destroyed  by  hot  alka- 
lies, but  withstand  the  action  of  mineral  acids  very  well.  They  are 
much  more  easily  injured  by  dry  heat  than  are  the  vegetable  fibres. 

VEGETABLE  FIBRES 

Vegetable  fibres  are  divided  into  two  groups,  —  seed  hairs,  con- 
sisting of  single  cells,  and  bast  fibres,  consisting  of  bundles  of  fibre- 
cells  joined  together  to  form  filaments  of  greater  or  less  length.  The 
most  important  vegetable  fibres  are  cotton,  flax  (linen),  hemp,  jute, 
China  grass,  and  esparto. 

Cotton  fibre  consists  of  the  seed  hairs  of  several  species  of  Gos- 
sypium,  plants  belonging  to  the  Malvaceae,  or  mallow  family.  The 
most  important  commercial  varieties  are  Gossypium  barbadense,  L. 
(Sea  Island  cotton),  G.  herbaceum,  L.,  or  G.  hirsutum,  L.  (upland 

487 


488 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


cotton  of  the  southern  states),  G.  arboreum,  L.  (Indian  and  Egyptian), 
and  G.  Peruvianum,  Cav.  (Brazil,  Peru,  and  neighboring  countries). 
The  varieties  are  distinguished  by  difference  in  the  length  and  fine- 
ness of  the  fibre  or  staple.  The  following  table  *  shows  the  average 
length  and  diameter  in  inches  of  the  principal  commercial  grades :  — 


Sea  Island  

LENGTH  OF  STAPLE 

DIAMETER 
OF  STAPLE 

Max. 

Min. 

Average 

1.80 

1.60 
1.06 
1.52 
1.31 
1.02 

1.41 

.88 
.81 
1.30 
1.03 

.77 

1.61 
1.02 
.93 
1.41 
1.17 
.89 

.000640 
.000775 
.000763 
.000655 
.000790 
.000844 

New  Orleans    . 

Upland   

Egyptian 

Brazilian     

Indian 

Thus  it  will  be  seen  that  the  longest  fibres  have  the  least  diameter ; 
they  are  also  silkier,  and  can  be  spun  into  the  finest  threads. 

The  fibres  are  attached  thickly  to  the  surface  of  the  seed,  and  as 
they  develop  a  mass  of  lint  is  formed  which  ultimately  bursts  the 
enclosing  pod  or  boll.  Each  fibre  consists  of  a  single  long  cell ;  but 
as  it  grows  the  cell  walls  become  thinner,  and  finally  collapse  to  form 
a  flat  tube.  After  the  boll  bursts  the  liquid  cell  content  solidifies 
by  exposure  to  the  sun  and  air,  the  dissolved  matters  are  deposited 
somewhat  irregularly  on  the  different  parts  of  the  cell  wall,  and,  con- 
sequently, the  fibre  twists  into  a  spiral  shape.  Thus,  as  seen  under 
the  microscope,  cotton  fibre  appears  as  an  irregular,  twisted,  and 
flattened  tube,  tapering  to  a  point  at  one  end.  The  unripe  fibres 
are  comparatively  straight,  but  if  made  into  yarn  they  twist  and 
curl,  and  are  of  little  value ;  being  difficult  to  dye,  they  cause  specks 
in  the  dyed  goods. 

Cotton  fibre  consists  essentially  of  cellulose  enclosed  in  a  film  or 
outside  skin  of  modified  cellulose.  On  the  surface  is  a  deposit  of 
wax  and  oily  matter  which  protect  it  from  the  action  of  moisture, 
and  which  is  removed  in  the  bleaching  process  before  dyeing  or  print- 
ing the  cotton  goods.  The  cellulose  of  the  fibre  is  scarcely  affected 
by  cold  dilute  mineral  acids,  but  if  allowed  to  dry  on  the  fibre  the 
acid  quickly  attacks  it.  Concentrated  sulphuric  acid  converts  cotton 
into  a  gelatinous  mass,  from  which  water  precipitates  a  starch-like 
body  called  amyloid. f  By  longer  action  of  the  strong  acid,  cotton  is 

*  Walter  H.  Evans,  Bulletin  No.  33,  U.  S.  Dept.  of  Agriculture,  p.  77. 
t  Parchment  paper  is  produced  by  the  short  action  of  strong  acid  on  paper, 
whereby  a  layer  of  amyloid  is  formed  on  the  surface. 


TEXTILE    INDUSTRIES  489 

converted  into  a  soluble  compound  (cellulose  sulphuric  acid),  then 
into  dextrin,  and  finally  into  dextrose. 

Boiling  in  dilute  alkalies  has  no  injurious  action  on  cotton  if  the 
air  is  excluded ;  otherwise  there  may  be  more  or  less  formation  of 
oxycellulose,  which  may  weaken  the  fibre.  When  treated  with  caustic 
soda  solution  at  50°  Tw.,  the  fibre  becomes  rounded,  swollen,  and 
semi-transparent,  and  the  interior  cavity  almost  disappears,  while 
a  marked  shrinkage  in  length  takes  place.  It  gains  in  weight  and 
in  strength,  while  its  affinity  for  coloring  matter  is  much  increased. 
The  fibre  probably  enters  into  combination  with  the  alkali  to  form  a 
compound  of  the  formula  Ci2H2oOio  •  Na2O,  or  C^H^oOio  •  2  NaOH, 
which  decomposes  with  water  to  form  hydrocellulose,  C^H^oOio  •  H^O. 
This  action  was  discovered  by  John  Mercer,  hence  the  name  "  mer- 
cerized cotton  "  applied  to  fibre  which  has  been  so 'treated. 

Mercerizing  is  extensively  employed  for  producing  a  high  lustre 
on  cotton  goods,  so  that  it  has  a  silky  appearance.  The  material  is 
held  under  tension  on  a  frame  while  being  treated  with  the  caustic 
soda  and  until  the  caustic  is  washed  out ;  or  tension  may  be  applied 
after  the  alkali  treatment  and  before  the  caustic  is  washed  away. 
Stretching  after  washing  does  not  produce  a  lustre.  The  tension 
prevents,  to  a  great  extent,  the  shrinkage  which  would  otherwise 
occur,  but  excessive  stretching  is  said  to  decrease  the  lustre ;  appar- 
ently, less  force  is  required  to  keep  the  cotton  at  its  original  length 
during  mercerization  than  to  draw  it  back  to  its  first  length  after- 
ward. The  cotton  is  thoroughly  wet  out  before  mercerizing,  to  in- 
sure even  action  on  the  fibre.  Special  machines  are  used  for  yarn, 
warps,  and  cloth,  the  object  of  each  being  to  prevent  contraction  and 
give  even  impregnation. 

The  time  of  washing  is  shortened  by  rinsing  in  water,  then  reliev- 
ing the  tension  and  washing  with  dilute  acetic  or  sulphuric  acid,  at 
0.5°  Be.,  while  the  temperature  is  raised  to  about  50°  C. 

Lange  *  describes  the  cotton  fibre,  mercerized  under  tension,  as  a 
straight,  translucent  tube,  and  he  supposed  the  lustre  to  be  caused 
by  the  parallel  reflection  of  light  rays  from  the  smooth  surfaces. 
Hiibner  and  Popef  hold  that  the  mercerizing  liquid  causes  first  a 
swelling  and  then  an  untwisting  of  the  natural  folds  of  the  fibre ;  the 
ends  being  more  or  less  firmly  held,  the  untwisting  of  the  swollen 
fibre  produces  the  appearance  of  a  "  gelatinous  straight  rod,  in  which 
a  series  of  pieces  of  corkscrew-like  windings  are  visible,"  thus  forming 

*  Farberzeitung,  1898,  197. 

t  J.  Soc.  Chem.  Ind.,  1904,  410. 


490  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

spiral  ridges,  with  rounded  edges,  on  its  surface,  which  reflect  the 
light  falling  on  them  from  any  direction. 

The  compound  Ci2H2oOio  •  2  NaOH  is  called  alkali  cellulose  ;  when 
exposed  to  the  action  of  carbon  disulphide  fumes,  a  cellulose  thio- 
carbonate  or  xanthate  is  formed.  This  body,  when  beaten  with  water, 
forms  a  thick  solution  called  "  viscose,"  which  is  easily  decomposed 
by  heat  or  certain  salts,  producing  cellulose  hydrate  and  free  alkali, 
and  liberating  carbon  disulphide.  By  squirting  viscose  through  fine 
capillary  tubes  and  causing  this  decomposition,  a  thread  of  cellulose 
having  a  silky  lustre  is  produced.  This  viscose  silk  is  very  tender 
when  wet,  but  is  brilliant  and  takes  dyes  well.  Viscose  is  also  used 
for  paper  sizing,  as  a  fixing  agent  in  textile  printing,  and  as  a  cement. 

By  treating  cellulose  with  acetic  anhydride  in  the  presence  of  a 
little  phenol-sulphonic  acid  at  80°  C.,  cellulose  tri-acetate  is  produced. 
It  dissolves  in  chloroform,  and  acetylene  tetrachloride,  but  is  in- 
soluble in  water,  and  is  used  for  films,  waterproofing,  insulation,  and 
other  purposes. 

Flax  or  linen  is  the  bast  fibre  of  the  flax  plant,  Linum  usitatissi- 
mum,  L.  The  individual  fibres  are  long  cylindrical  cells,  pointed  at 
the  ends,  and  having  thick  walls  with  a  narrow  central  cavity.  Each 
fibre  is  marked  with  transverse  bands,  and  has  a  glistening  surface. 
The  average  length  is  from  2  to  4  cm. ;  the  individual  cells  are  united 
in  bundles,  firmly  glued  together,  consequently  linen  is  much  less 
elastic  than  cotton  fibre,  next  to  which  it  ranks  in  importance  among 
vegetable  fibres.  In  warm  countries  flax  is  raised  chiefly  for  the  seed. 
(See  Linseed  Oil,  p.  357.)  That  grown  in  temperate  climates  has 
much  the  better  fibre.  It  is  pulled  up  by  the  roots  before  the  seeds 
ripen,  and  is  immediately  subjected  to  the  process  of  "  rippling,"  i.e. 
it  is  drawn  through  the  teeth  of  a  coarse  comb  to  detach  the  seeds. 
To  separate  the  bast  fibre  from  the  rind,  woody  tissue,  and  pith,  the 
flax  is  "  retted."  This  may  be  done  in  five  different  ways :  — 

(a)  Retting  in  stagnant  water  is  practised  in  Ireland  and  to  some 
extent  in  Russia.     The  flax  is  put  into  pools  of  soft  water  and  left 
until  bacterial  action  sets  in ;    this  softens  and  partly  destroys  the 
gummy  and  resinous  matter  cementing  the  fibres  to  the  ligneous 
tissue.     Great  care  is  necessary  that  the  bast  fibres  themselves  are 
not  attacked.     The  fermentation  is  often  very  offensive.     When  it 
has  gone  far  enough,  the  flax  is  exposed  to  the  action  of  the  air  and 
sunlight  for  several  days  ("  grassed  "). 

(b)  Retting  in  running  water  is  extensively  practised  in  France 


TEXTILE    INDUSTRIES  491 

and  Belgium.  The  flax  is  put  into  crates  and  submerged  in  streams. 
The  fermentation  takes  place  as  above,  but  requires  a  longer  time. 
The  coloring  matter  is  washed  away,  and  a  lighter  colored  product  is 
obtained. 

(c)  Dew  retting  consists  in  exposing  the  damp  flax  to  the  weather 
for  several  weeks.     The  fermentation  takes  place  much  as  above. 

(d)  Retting  in  water  at  30°  to  35°  C.  hastens  the  fermentation 
greatly,  so  that  it  is  generally  complete  in  about  three  days.     The 
flax  is  often  passed  between  squeeze  rolls,  to  assist  in  detaching  the 
woody  fibre.     By  treating  the  flax  with  water  and  steam  under  press- 
ure, it  is  rapidly  retted,  and  the  fibre  has  a  silky  lustre. 

(e)  Mineral  acids  are  sometimes  used  in  stagnant-water  retting, 
to  prevent  the  offensive  odor.     By  digesting  the  flax  in  very  dilute 
hydrochloric  acid,  followed  by  a  weak  alkali  bath,  the  retting  is 
quickly  finished. 

Various  mechanical  processes  are  employed  to  detach  the  ligneous 
matter  from  the  fibre  after  retting.  Breaking  consists  in  crushing 
the  flax  with  grooved  rolls ;  after  this  it  is  "  scutched,"  i.e.  the  crushed 
mass  is  pounded  by  hand  in  a  machine,  to  remove  the  loosened  matter. 
Heckling  is  a  combing  process  to  draw  the  fibres  parallel  and  make 
them  suitable  for  spinning. 

Linen  fibre  is  not  so  pure  cellulose  as  cotton,  but,  in  general,  acts 
like  the  latter.  It  is  stronger,  has  more  natural  lustre,  is  more  diffi- 
cult to  bleach  and  dye,  and,  being  a  better  conductor  of  heat,  feels 
cold  to  the  touch. 

Hemp  is  the  bast  fibre  of  Cannabis  sativa,  L.,  which  is  largely  cul- 
tivated in  Russia  and  Italy.  The  fibres  are  separated  from  the  wood 
and  pith  of  the  stalks  in  the  same  general  way  as  flax.  They  are 
stronger  and  coarser  than  flax,  and,  being  more  deeply  colored,  are 
mainly  used  for  rope,  coarse  canvas,  and  bagging. 

Jute  is  the  bast  fibre  of  several  species  of  Corchorus,  of  which  C. 
capsularis,  L.,  is  the  most  important.  The  plants  are  indigenous  to 
India,  and  their  cultivation  is  mainly  confined  to  India  and  Ceylon, 
though  some  has  been  raised  in  Louisiana  and  Mississippi.  The 
fibre  is  obtained  by  simple  retting  in  water.  It  is  very  long,  some- 
times reaching  two  meters,  but  the  fibre  cells  are  short,  and  the 
filaments  are  not  so  strong  as  those  of  flax  or  hemp.  The  fibre  is 
light  yellow,  and  has  a  high  lustre.  It  is  quite  susceptible  to  the 
action  of  acids  and  alkalies,  and  is  easily  destroyed  by  mineral 
acids.  Much  care  is  required  to  bleach  it  with  bleaching  powder, 


492  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

since  the  weakening  of  the  fibre  is  excessive.  Sodium  peroxide  gives 
the  best  bleach  on  this  material;  or  potassium  permanganate,  fol- 
lowed by  sulphurous  acid,  may  be  used.  It  differs  in  its  chemical 
composition  from  cotton  and  flax.  Its  cellulose  is  all  combined  with 
lignified  tissue,  forming  bastose.  Jute  resembles  cotton  which  has  been 
mordanted  with  tannin,  and  can  be  dyed  directly  with  basic  dyes. 

China  grass,  or  ramie,  is  a  bast  fibre  derived  from  Bcehmeria 
nivea,  Gaud.,  a  species  of  nettle  cultivated  in  China  and  Eastern 
Asia.  The  fibre  is  difficult  to  detach  from  the  ligneous  matter ;  ret- 
ting usually  divides  it  into  its  component  cells,  which  cannot  then 
be  separated  from  the  stem  and  bark.  It  is  customary  to  separate 
the  fibres  by  crushing  the  green  stalk  and  washing  away  the  woody 
matter  with  running  water,  but  this  method  is  expensive.  The  fibre 
has  a  brilliant  lustre  (which  dyeing  is  liable  to  injure),  and  is  easily 
bleached.  It  is  very  strong,  and  is  nearly  pure  cellulose. 

Esparto  is  a  grass  with  tough  fibre,  cultivated  in  Spain,  and  chiefly 
used  for  cordage  and  paper  making. 

Manila  hemp  and  sisal  are  used  as  substitutes  for  hemp.  The 
former  is  obtained  in  the  Philippine  Islands,  from  the  leaves  of  a 
wild  plantain,  Musa  textilis,  Nee.,  and,  being  tough  and  light,  is  much 
used  for  cordage  and  ropes.  Sisal  is  obtained  from  an  agave  plant, 
Agave  rigida,  Mill.,  and  A.  Americana,  L.,  in  Central  America  and 
the  West  Indies.  It  is  chiefly  used  for  burlap  as  a  substitute  for  jute. 

Other  vegetable  fibres  of  small  importance  are  cocoanut  fibre,  from 
the  husk  of  the  cocoanut,  used  for  brushes,  mats,  and  cordage ;  New 
Zealand  flax,  a  long  fibre  prepared  from  a  New  Zealand  plant,  Phor- 
mium  tenax,  Forst.,  and  chiefly  used  for  ropes  ;  Sunn  hemp,  an  Indian 
plant,  furnishes  a  fibre  suitable  for  ropes  and  cordage. 


ANIMAL  FIBRES 


Of  animal  fibres,  only  silk  and  wool  are  of  much  technical  im- 
portance. Silk  fibre  forms  the  cocoon  of  the  silkworm,  Bombyx  mori. 
The  worm  has  two  glands,  situated  on  either  side  of  its  body,  each 
connected  by  a  duct  with  a  capillary  opening  (spinneret)  in  the  worm's 
head.  These  glands  each  appear  to  secrete  two  transparent  liquids ; 
the  one,  fibroine,  CisHsaNsOe,*  constituting  from  one-half  to  two-thirds 
of  the  whole  secretion,  forms  the  interior  and  larger  part  of  the  silk 
fibre ;  the  other,  sericine,  CisH^^Os,*  also  called  silk  glue,  is  yellowish 
in  color  and  is  readily  dissolved  in  boiling  water,  hot  soap  solution's, 

*  According  to  Mulder, 


TEXTILE   INDUSTRIES  493 

or  by  alkalies.  It  forms  the  outer  coating  of  the  fibre.  As  soon  as 
discharged  into  the  air,  the  fluids  from  the  spinnerets  solidify,  and 
coming  in  contact  with  each  other  at  the  moment  of  discharge,  are 
firmly  cemented  together  by  the  sericine  ;  hence,  under  the  microscope 
the  fibre  shows  two  separate  structureless  filaments.  The  cocoon  is 
made  up  of  one  continuous  fibre,  from  350  to  1200  meters  long,  with 
an  average  diameter  of  .018  mm. 

Silkworms  are  raised  from  eggs  kept  in  an  incubator  from  twelve 
to  eighteen  days,  while  the  temperature  is  slowly  raised  from  .18° 
to  25°  C.  The  caterpillars  have  a  prodigious  appetite,  and  are 
fed  regularly  on  mulberry  leaves  (Morus  alba,  L.)  for  about  thirty 
days,  during  which  time  they  grow  rapidly,  casting  their  skins  every 
five  or  six  days,  and  attaining  a  length  of  about  8  cm.  Then  they 
cease  to  eat,  and  crawl  upon  twigs,  where  they  spin  their  cocoons. 
This  spinning  requires  about  three  days,  when  the  worms  are  killed 
by  heating  the  cocoons  in  an  oven  at  60°  to  70°  C.  for  three  hours,  or 
by  steaming  them  for  10  or  15  minutes.  After  sorting,  the  cocoons 
are  reeled.  This  is  an  entirely  mechanical  process  requiring  much 
skill.  The  cocoons  are  soaked  in  water  at  60°  C.,  until  the  silk  glue 
is  softened.  Then  the  operator  catches  the  loose  ends  of  several 
fibres  on  a  small  brush,  and  passes  them  through  the  agate  or  porce- 
lain guides  of  the  reel,  where  they  are  twisted  to  form  threads  of  suffi- 
cient size  for  weaving.  Two  threads  are  formed  simultaneously  on 
each  reel,  and  are  made  to  cross  and  rub  against  each  other  to  remove 
kinks  and  to  straighten  them,  and  also  to  rub  the  softened  silk-glue 
coverings  together,  so  that  the  fibres  adhere  and  form  solid,  uniform 
threads,  —  raw  silk.  There  is  considerable  waste,  consisting  of  short 
and  tangled  fibre  from  the  exterior  of  the  cocoons,  and  from  those 
which  have  been  opened  by  the  moth  in  escaping.  This  is  worked 
up  as  floss,  and  for  making  spun  silk. 

Raw  silk  is  exceedingly  hygroscopic,  and,  under  favorable  circum- 
stances, will  absorb  as  much  as  30  per  cent  of  its  weight  of  moisture, 
and  still  seem  quite  dry.  It  is,  therefore,  customary  to  determine  the 
moisture  in  each  lot  at  the  time  of  sale.  This  is  called  "  condition- 
ing," and  must  be  done  with  great  care,  usually  in  official  laboratories. 
A  sample  is  taken  from  each  bale,  and,  after  careful  weighing,  is  dried 
in  a  current  of  air  in  a  special  apparatus,  at  a  temperature  of  110°  C., 
until  the  weight  becomes  constant.  From  the  average  of  several  tests 
the  absolute  amount  of  dry  silk  is  determined,  to  which  the  legal 
amount  of  moisture  permissible  (11  per  cent)  is  added,  and  the  result 
taken  as  the  weight  of  the  raw  silk, 


494  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

Raw  silk  consists  of  about  25  per  cent  sericine,  the  remainder 
being  pure  fibroine,  and  has  a  harsh  feel  and  is  stiff  and  coarse. 
Before  it  is  made  into  yarn  or  cloth,  it  is  usually  subjected  to  various 
treatments  to  make  it  soft  and  glossy.  The  first  process  is  called 
discharging,  stripping,  or  ungumming,  and  its  purpose  is  to  remove 
more  or  less  of  the  silk  glue  (sericine)  from  the  fibre,  according  to  the 
kind  of  goods  desired.  The  hanks  of  silk  are  suspended  on  wooden 
sticks  in  a  vat  filled  with  soap  solution  at  95°  C.  This  is  made  by 
dissolving  Marseilles,  or  olein  soap  to  the  amount  of  30  per  cent  of 
the  weight  of  the  silk,  in  soft  water,  free  from  lime.  The  hanks 
are  turned  several  times  by  hand  in  this  liquor,  during  a  period 
of  from  one  to  one  and  a  half  hours ;  the  fibres  swell,  become  sticky, 
and  finally  the  sericine  dissolves,  leaving  the  silk  glossy  and  soft. 
The  soap  bath  is  not  boiled,  as  that  would  tangle  the  fibres  and  cause 
the  yellow  color  often  present  in  the  sericine  to  become  fixed  on  them ; 
also  long  boiling  weakens  silk.  For  very  fine  work,  two  or  three  soap 
baths  are  employed,  the  raw  silk  being  first  put  into  that  which  has 
been  longest  in  use  and  which  is  therefore  strongly  charged  with  dis- 
solved sericine ;  *  there  the  glue  is  softened  and  partly  removed ;  the 
hanks  are  transferred  to  the  succeeding  baths  in  order,  finally  leaving 
the  one  most  recently  prepared.  This  yields  soft,  white  silk,  which 
is  rinsed  in  a  warm  dilute  sodium  carbonate  solution  and  then 
wrung.  That  which  is  to  be  sold  as  white  silk  or  dyed  a  very  light 
shade  is  then  subjected  to  a  second  discharging  process,  in  which  the 
hanks  are  tied  in  several  places  with  tape,  enclosed  in  linen  bags,  and 
boiled  in  a  15  per  cent  soap  solution  from  one-half  to  three  hours,  to 
remove  all  the  glue.  This  product,  called  "  boiled-off  silk,"  has  lost 
from  20  to  30  per  cent  of  its  original  weight.  In  order  to  reduce  this 
loss  of  weight,  raw  silk  is  often  treated  in  a  weak  soap  bath  until  the 
waxy  matters  have  been  partly  removed,  and  is  then  washed  and  some- 
times bleached  by  exposure  to  sulphur  dioxide  vapors.  The  product, 
called  "  ecru  silk,"  is  harsh  to  the  touch,  but  has  lost  only  about  from 
2  to  4  per  cent  of  its  original  weight ;  it  is  chiefly  used  in  the  warp  of 
black  silk  and  for  the  back  of  velvet. 

Another  process  f  of  treating  raw  silk  for  dyeing,  while  leaving 
a  large  part  of  the  sericine  on  the  fibre,  is  employed  for  producing 
souple  silk.  The  hanks  are  first  scoured  in  a  10  per  cent  soap  solu- 

*  The  soap  liquor  finally  becomes  heavily  charged  with  sericine  and  is  drawn 
from  the  tank  as  "  boiled-off  liquor."  It  is  used  in  making  up  the  dye  bath  for 
silk  dyeing,  pp.  532,  534,  and  536. 

f  Chemische  Technologic,  Wagner. 


TEXTILE    INDUSTRIES  495 

tion  for  an  hour  or  two  at  25°  to  35°  C.  to  soften  and  swell  the  fibres. 
They  are  then  bleached  by  working  for  10  or  15  minutes  in  very  dilute 
aqua  regia.  The  bleached  silk  is  theji  exposed  to  sulphur  fumes  for 
several  hours,  until  sufficiently  white.  It  is  then  soupled,  i.e.  worked 
for  an  hour  and  a  half  in  a  solution  of  cream  of  tartar  or  magnesium 
sulphate,  3  or  4  grams  to  the  liter.  This  swells  and  softens  the  fibre, 
which  was  left  harsh  by  the  bleaching  process.  Soupled  silk  has  lost 
only  6  or  8  per  cent  of  its  original  weight,  but  is  weaker  than  boiled- 
off  silk. 

Concentrated  mineral  acids,  especially  hydrochloric,  dissolve  silk 
completely.  Very  dilute  acids  are  absorbed  by  it,  thus  increasing 
the  lustre  and  imparting  a  peculiar  feel  to  the  fibre,  which  when 
compressed  emits  a  curious  rasping  sound  called  "  scroop."  The 
property  of  scroop  may  be  given  by  treating  the  silk  in  a  bath  of  di- 
lute acetic,  or  tartaric  acid,  and  drying  without  washing.  Caustic 
alkalies  in  strong  solution  rapidly  destroy  silk  if  heated;  but  in 
cold  solution,  caustic  soda  of  50°  Tw.  has  little  action  on  the  fibre 
and  may  be  used  to  produce  on  mixed  cotton  and  silk  goods  the 
crinkled  appearance  shown  by  seersuckers.  Ammonia  has  little  or 
no  action  on  the  fibroine  but  dissolves  the  sericine.  Alkaline 
carbonates  are  less  destructive  than  caustic,  but  attack  the  fibre 
slowly.  Borax  dissolves  sericine  without  material  injury  to  the 
fibroine,  but  is  not  so  good  as  soap  for  ungumming  raw  silk.  Lime- 
water  swells  the  fibre,  makes  it  brittle,  and  dulls  the  lustre.  Chlorine 
destroys  silk  as  do  other  oxidizing  agents  unless  used  very  dilute 
and  with  much  care.  When  soaked  in  solutions  containing  metallic 
salts,  especially  iron,  aluminum,  tin,  lead,  or  copper,  silk  absorbs 
some  of  the  salt  and  a  precipitation  of  basic  salt  within  and  upon  the 
fibre  occurs.  On  this  fact  depends  the  weighting  of  silks  (p.  515). 

Besides  the  cultivated  silks,  certain  kinds  of  wild  silks  are  of 
some  commercial  importance.  The  most  important  is  tussah  silk, 
obtained  from  the  cocoons  of  Indian  and  Chinese  moths,  Antherasa 
mylitta  and  A.  pernyi.  The  fibre  is  double  and  somewhat  flat,  each 
filament  being  composed  of  a  number  of  fibrillse.  It  is  brown  in 
color,  is  stiffer  and  coarser  than  ordinary  silk,  and  differs  in  its  chemi- 
cal composition,  containing  less  carbon  and  nitrogen  and  more  oxygen. 
It  is  more  resistant  to  the  action  of  alkalies  and  acids  and  to  bleaching 
agents.  It  is  difficult  to  bleach  and  dye,  and  is  chiefly  employed  in 
making  pile  fabrics,  such  as  velvets,  plush,  and  imitation  sealskin. 
Other  wild  silks  are  muga  silk  from  Anthercea  Assama,  and  eria  silk 
from  Attacus  ricini,  both  found  in  India;  yamamai  silk,  from  An- 


496  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

thercea  yamamai  of  Japan  ;  sea-silk  or  byssus,  produced  by  a  mollusk, 
Pinna  nobilis,  found  in  the  Mediterranean  Sea.  The  fibre  of  sea- 
silk  is  brown  and  very  soft,  and  is  not  easily  affected  by  acids  or 
alkalies. 

The  following  analyses  from  Hummers  Dyeing  of  Textile  Fabrics 
are  of  interest. 

Composition  of  the  cocoons  :  — 

Moisture 68.2 

Silk 14.3 

Floss 0.7 

Chrysalis 16.8 

Composition  of  raw  silk :  — 

YELLOW  ITALIAN  SILK          WHITE  LEVANT  SILK 

Fibroine 53.37  ....  54.04 

Gelatine 20.66  ....  19.08 

Albumin 24.43  ....  25.47 

Wax 1.39  ....  1.11 

Coloring  matter       .     .     .       0.05  ....  0.00 

Resinous  and  fatty  matter        0:10  ....  0.30 

100.00  100.00 

The  ultimate  analysis  of  silk  fibroine  is  shown  in  the  following 
table:*  — 

TUSSAH  FIBROINE  MULBERRY  FIBROINE 

(Calculated  for  CisH^sNsOe) 

Carbon    .....       47.18  ......  47.78 

Hydrogen     ....         6.30 6.23 

Nitrogen 16.85  .     .    '.*".     .     .  18.90 

Oxygen    .'.    V    .    (>       29.67  .  A     .     .     .'     .  26.04 

100.00  .....     .     .  98.95 

Artificial  silk  is  made  from  cellulose  by  several  processes,  and  also 
from  gelatine  or  casein,  but  only  the  cellulose  products  are  now  im- 
portant. 

(a)  The  Chardonnet-Lehner  process  uses  collodion  (p.  479)  contain- 
ing about  15  per  cent  of  pyroxyline  in  solution  in  alcohol-ether  mix- 
ture, amyl  acetate,  or  acetylene  tretrachloride.  The  filtered  solution 
is  forced,  under  60  atmospheres  pressure,  through  capillary  glass  tubes, 
into  a  chamber  where  it  meets  a  current  of  air  to  evaporate  the  sol- 
vent and  coagulate  the  pyroxyline,  which  forms  filaments  closely 
resembling  natural  silk  fibre  in  appearance ;  several  of  the  filaments 
are  twisted  into  a  fibre,  which  after  washing  in  water  is  "  denitrated  v 
by  treatment  with  a  cold  dilute  solution  of  ammonium  or  sodium  sul- 

*  Manual  of  Dyeing,  Knecht,  Rawson,  and  Loewenthal,  p.  55. 


TEXTILE    INDUSTRIES  497 

phide.  This  reduces  the  nitrate  forming  hydrated  oxycellulose,  which 
retains  the  silky  lustre,  and  is  no  more  inflammable  than  cotton. 
The  fibres,  after  washing  and  drying,  are  combed  and  spun  into  yarn, 
which  has  less  strength  than  natural  silk,  however. 

(b)  The  Pauly-Fremery  process  uses  a  solution  of  mercerized  cotton 
in  ammoniacal  copper  oxide  liquor.     The  filtered  solution  is  squirted 
through  capillary  glass  tubes  into  dilute  (18°  Be.)  sulphuric  acid,  or  a 
5  per  cent  caustic  soda  liquor,  which  precipitates  hydrocellulose.  After 
washing  and  drying  the  fibre  possesses  a  very  high  lustre. 

(c)  Viscose  silk  is  made  by  forcing  a  thick  solution  of  cellulose 
thiocarbonate  (p.  490)  into  ammonium  sulphate  liquor,  which  precipi- 
tates hydrocellulose  as  a  fibre.     After  washing  free  from  alkali,  the 
material  is  spun  into  yarn  having  a  high  lustre.     It  is  somewhat 
cheaper  than  the  other  varieties  and  its  use  is  increasing  rapidly. 
The  viscose  solution  is  made  directly  from  wood  pulp. 

(d)  Cellulose  acetate  silk  is  made  by  squirting  a  solution  of  cellulose 
acetate   (p.  585)  in  acetylene  tetrachloride,  to  form  fine  filaments 
which  are  spun  into  yarn.     It  is  not  very  inflammable  and  has  high 
lustre,  but  is  not  readily  dyed  in  aqueous  baths. % 

Artificial  silk  fibres  can  be  fused  together  to  form  artificial  horse- 
hair and  bristles,  which  are  now  of  considerable  commercial  importance. 

Much  mercerized  cotton  (p.  489)  is  now  prepared  to  imitate  silk. 

Wool  is  the  hair  of  the  sheep,  but  that  of  certain  goats,  such  as 
the  alpaca,  cashmere,  and  mohair,  as  well  as  that  of  the  camel,  is 
also  classed  with  wools.  Wool  differs  from  true  hair  only  in  its 
physical  structure,  being  covered  with  minute  overlapping  scales  and 
having  a  twisted  or  curled  fibre.  The  character  of  wool  varies  with 
the  breed,  food,  and  care  of  the  sheep,  and  the  climate  and  nature  of 
the  soil  on  which  the  food  is  grown.  The  fibre  varies  from  short, 
fine,  and  wavy,  to  long,  coarse,  and  straight  in  different  breeds.  The 
length  ranges  from  1  inch  to  10  inches  in  different  varieties,  even 
reaching  16  inches  in  the  case  of  certain  cashmeres  and  mohairs. 
The  wool  cut  from  one  animal  is  called  a  fleece,  and  the  different 
grades  in  each  fleece  are  separated  by  hand,  that  from  the  neck,  back, 
and  shoulders  being  the  longest  and  best  quality.  The  long  staple 
wools  have  a  silky  appearance  and  are  often  called  lustre  wools. 
They  are  generally  used  for  worsted  goods,  while  the  short,  fine  wools 
are  made  into  woollen  goods.  Mohair,  obtained  from  the  Angora 
goat,  has  a  high  lustre  and  is  soft  and  fine,  as  are  also  the  alpaca, 
vicuna,  and  llama  wools  derived  from  South  American  goats. 

Sheep  pelts  are  often  soaked  in  "  milk  of  lime/'  or  sodium  sul- 

2K 


498  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

phide,  to  loosen  the  wool  before  making  leather  from  the  skin.  Such 
wool  is  known  as  "  pulled  wool,"  and  is  of  inferior  quality. 

Wool  is  very  hygroscopic,  and  may  contain  from  8  to  12  per  cent 
of  moisture  in  hot,  dry  weather,  up  to  50  per  cent  in  very  damp  air. 
On  an  average,  it  contains  about  18.25  per  cent,  and  this  is  the  legal 
limit  in  most  European  countries,  and  is  generally  determined  in 
"  conditioning  laboratories,"  as  in  the  case  of  silk.  The  temperature 
of  drying  is  kept  between  105°  and  110°  C.,  since  above  this  temper- 
ature there  is  danger  of  injuring  the  fibre.  At  100°  C.  wool  becomes 
plastic,  and  after  cooling  retains  the  shape  into  which  it  may  have 
been  formed  while  hot. 

Each  wool  fibre  is  covered  with  a  layer  of  broad  scales,  projecting 
in  the  same  direction  and  overlapping  much  like  shingles  on  a  roof, 
the  outer  edges  being  more  or  less  free.  When  the  approximately 
parallel  fibres  are  moved  upon  each  other  by  rubbing  or  "  milling," 
the  scales  interlock  and  cause  "  felting."  The  interior  substance  of 
the  fibre  is  composed  of  narrow  cells  tapering  towards  each  end. 
Some  wools  also  have  a  central  or  medullary  part,  made  up  of  cells  of 
different  shape,  and  which  usually  contain  the  coloring  matter  of  the 
fibre.  Such  wools  are  stiff  and  brittle,  and  resemble  hair  in  their 
properties ;  the  best  wools  are  free  from  such  medullary  cells. 

The  internal  cells  appear  to  have  more  attraction  for  dyes  than 
do  the  outer  horny  scales,  and  much  of  the  effect  of  acids  and  other 
additions  to  the  dye-bath  is  supposed  to  be  due  to  the  raising  of 
these  scales  by  their  action,  thus  permitting  the  access  of  the  dye  to 
the  interior  substance.  Diseased  and  dead  fibres,  known  as  "  kemp," 
do  not  color  well,  since  they  have  a  very  impenetrable  layer  of  these 
scales ;  moreover,  they  do  not  felt  properly,  and  are  dull  in  lustre. 

Pure  wool  fibre,  consisting  for  the  most  part  of  keratine,  the 
characteristic  constituent  of  horn,  feathers,  etc.,  is  not  of  constant 
chemical  composition,  varying  in  different  qualities  and  kinds.  The 
approximate  composition  of  keratine  from  wool  is :  — 

Carbon 49.25* 

Nitrogen 15.86 

Hydrogen 7.57 

Sulphur 3.66 

Oxygen 23.66 

The  presence  of  sulphur  is  characteristic  of  wool,  and  often  causes 
difficulties  in  mordanting  and  dyeing.     The  ash  of  the  fibre  averages 
less  than  1  per  cent  of  the  weight  of  the  wool.     When  heated  to  130° 
*  Hummel,  Dyeing  of  Textile  Fabrics. 


TEXTILE    INDUSTRIES  499 

C.,  with  water  under  pressure,  and  dried,  wool  is  rendered  very  brittle. 
Dilute  acids  have  no  apparent  action  on  it,  but  a  small  percentage 
is  absorbed  and  cannot  be  readily  removed  by  washing;  concen- 
trated mineral  acids  destroy  the  fibre.  By  treating  mixed  cotton  and 
wool  goods  with  a  dilute  sulphuric  or  hydrochloric  acid,  and  drying 
at  110°  C.,  the  cotton  is  "carbonized"  (p.  501),  and  when  heated 
crumbles  to  dust  and  falls  away  from  the  unchanged  wool.  The  same 
result  is  obtained  by  treating  the  goods  with  hot,  dry  hydrochloric 
acid  gas.  Alkalies  attack  wool  energetically,  the  caustic  alkalies 
and  lime  being  most  destructive,  especially  in  boiling  solution,  by 
which  the  fibre  is  completely  destroyed.  Alkaline  carbonates  are 
much  less  injurious,  and  are  used  in  dilute  solution  for  scouring  wool. 
Ammonia  and  ammonium  carbonate  have  little  tendering  effect 
on  it,  and  are  best  for  washing,  for  which  soap,  borax,  and  sodium 
phosphate  are  also  used.  When  strong  and  allowed  to  act  for  some 
time,  oxidizing  agents  cause  the  fibre  to  become  tender.  Very  dilute 
solution  of  potassium  bichromate  is  largely  used  in  mordanting  wool, 
but  care  is  necessary  to  prevent  "  over  chroming."  When  moist, 
chlorine  is  taken  up  by  wool,  and  the  fibre  made  very  tender,  but  a 
slight  treatment  with  it  makes  the  wool  more  susceptible  to  cer- 
tain dyes ;  dry  chlorine  is  said  to  have  no  action.  WTool  is  colored 
yellow  by  hypochlorous  acid,  hence  bleaching  powder  is  not  used  to 
bleach  the  fibre.  When  boiled  in  solutions  of  various  metallic  salts, 
it  absorbs  a  considerable  amount  of  them,  and  it  is  often  so  treated 
when  mordanting  before  dyeing.  The  nature  of  the  reactions  occur- 
ring is  not  clear,  but  apparently  there  is  a  direct  union  between  the 
fibre  or  some  of  its  constituents  and  the  salt.  Wool  has  great  affinity 
for  many  dyes,  and  the  colors  produced  are  generally  faster  than  when 
dyed  on  cotton  or  silk. 

Before  it  can  be  subjected  to  any  manufacturing  process,  raw 
wool  must  be  washed  and  scoured  to  remove  impurities,  which  are 
present  to  the  extent  of  from  30  to  80  per  cent  of  the  total  weight. 
These  consist  of :  (a)  yolk  or  wool  grease,  and  (6)  suint,  which  exude 
from  the  body  of  the  animal  with  the  perspiration ;  and  (c)  dirt 
mechanically  mixed  with  them  or  entangled  among  the  fibres. 

The  wool  grease  is  soluble  in  ether,  benzene,  or  carbon  disulphide, 
and  is  made  up  of  bodies,  consisting  largely  of  solid  alcohols,  espe- 
cially cholesterine  and  isocholesterine,  together  with  the  oleic, 
palmitic,  and  stearic  acid  esters  of  those  alcohols.  These  substances 
are  not  easily  saponified  with  alkali,  but  can  be  emulsified  with  soap 
solution,  and  thus  easily  removed  from  the  fibre. 


500  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

Suint  is  soluble  in  water,  and  consists  mainly  of  potassium  salts 
of  oleic,  stearic,  valeric,  and  acetic  acids,  together  with  sulphates, 
chlorides,  and  phosphates,  and  nitrogenous  bodies. 

These  are  generally  removed  by  washing  in  a  solution  of  soap. 
A  soft  soap,  made  from  Gallipoli  oil  (p.  363),  is  preferred  for  the  best 
qualities  of  wool,  but  usually  a  cheaper  soap,  containing  some  sodium 
carbonate,  is  employed.  The  washing  is  done  in  machines,  and  care 
is  taken  not  to  entangle  the  fibre  any  more  than  need  be.  There  are 
usually  three  tanks,  placed  en  cascade,  and  so  arranged  that  the  wool 
may  be  automatically  passed  from  one  to  the  next,  while  the  liquor 
is  drawn  from  one  to  the  other  in  a  direction  opposite  to  the  move- 
ment of  the  wool.  The  raw  wool  is  introduced  into  the  soap  liquor 
containing  more  or  less  impurity  from  its  previous  use  in  the  other 
tanks.  The  temperature  should  be  from  35°  to  40°  C.  The  wool 
is  submerged  and  pushed  forward  a  short  distance  by  prongs  or 
forks  which  work  automatically.  At  each  stroke,  a  portion  of  the 
wool  is  pushed  between  squeeze-rolls,  which  expel  the  liquor;  it 
then  passes  into  the  next  tank,  where  it  is  washed  in  the  same  way 
with  cleaner  soap  liquor,  and  then  goes  through  squeeze-rolls  into 
the  last  tank,  containing  clear  water  or  fresh  soap  liquor.  The 
wash  liquor,  aided  by  the  free  alkali  added  and  the  potassium 
oleate,  etc.,  in  the  suint,  emulsifies  and  dissolves  the  wool  grease 
and  suint,  loosening  the  mechanical  impurities,  which  sink  to  the 
bottom.  After  washing  in  clean  water,  the  wool  is  "  centriffed," 
and  then  dried  on  wire  netting  by  a  current  of  warm  air.  The  foul- 
smelling,  dirty  brown  liquor  from  the  first  tank  is  drawn  off,  and  may 
be  evaporated  directly  and  calcined  to  recover  the  potash,  which 
amounts  to  from  1  to  8  per  cent  of  the  weight  of  the  wool.  Or  it  may 
be  treated  to  recover  the  wool  grease,  sometimes  called  Yorkshire 
grease ;  it  is  settled  to  remove  coarse  dirt,  and  then  sulphuric  acid  is 
added  in  slight  excess,  to  decompose  the  soaps  and  set  free  the  fatty 
acids,  which  rise  to  the  surface,  carrying  the  wool  grease  with  them. 
The  water  is  drawn  off  from  the  magma,  which  is  pressed,  hot,  in 
canvas  bags.  The  grease  is  kept  in  a  liquid  condition  until  all  sedi- 
ment deposits,  when  it  is  drawn  into  casks,  where  it  solidifies  on  cool- 
ing. It  is  used  as  a  lubricator,  and  in  leather  dressing. 

By  passing  the  clarified  wash  liquor  through  a  machine  similar  to 
a  cream  separator,  the  grease  is  very  neatly  separated  from  it.  For 
the  preparation  of  lanolin  from  this  grease,  see  p.  370. 

Wool  is  often  treated  by  methods  intended  to  recover  the  yolk 
and  suint  separately.  This  is  usually  done  by  extracting  first  with  a 


TEXTILE   INDUSTRIES  501 

volatile  solvent  (carbon  disulphide  or  petroleum  spirit)  to  remove  the 
wool  grease,  and  then  washing  the  wool  in  water  to  remove  the  suint. 

The  washed  wool  is  harsh  and  brittle,  and  before  being  manu- 
factured must  be  softened  by  oiling.  Pure  olive  oil  is  best  for  this, 
but  lard,  colza,  hemp,  peanut  and  mineral  oils,  and  sometimes  "red  oil " 
(oleic  acid)  are  also  used.  This  in  turn  must  be  removed  by  scouring 
before  dyeing. 

Wool  containing  much  straw,  burrs,  or  other  vegetable  matter 
is  often  cleaned  by  carbonizing.  The  raw  wool  is  submerged  in  a 
solution  of  aluminum  chloride  of  about  8°  Be.  for  25  to  30  minutes ; 
it  is  then  lifted  out,  "  centriffed,"  and  at  once  put  into  a  hot  room, 
where  the  absorbed  aluminum  chloride  is  decomposed,  and  the  hydro- 
chloric acid  formed  attacks  the  vegetable  matter,  making  it  so  friable 
that  it  falls  to  dust  when  the  wool  is  passed  through  a  beating  machine. 
Instead  of  aluminum  chloride,  a  solution  of  sulphuric  acid  may  be 
used  for  carbonizing. 

A  similar  process  is  used  to  separate  wool  fibre  from  cotton  or 
other  vegetable  fibre  in  rags  which  are  to  be  made  into  "  shoddy." 

BLEACHING 

Natural  fibres,  either  vegetable  or  animal,  always  contain  color- 
ing matters,  which,  even  though  present  in  very  small  quantities, 
impair  the  purity  of  the  white  desirable  in  most  uncolored  fabrics. 
And  there  are  always  certain  gums,  resins,  waxes,  and  oily  matters 
on  the  fibres,  either  natural  to  it  or  added  to  facilitate  spinning  and 
weaving.  In  woven  goods  there  is  more  or  less  sizing,  i.e.  starch, 
china  clay,  metallic  salts  or  oxides,  etc.,  put  upon  the  fibre  to  assist 
in  weaving  or  to  improve  the  appearance  or  weight  of  the  cloth. 
These  substances  prevent  the  proper  action  of  mordants  and  dyes, 
or  detract  from  the  appearance  of  those  fabrics  to  be  sold  undyed, 
and  the  bleacher  must  remove  them  and  decolorize  the  fibre. 

In  general,  the  bleaching  process  is  divided  into  two  stages,  the 
washing  or  scouring  and  the  bleaching  proper  or  chemical  treatment 
which  varies  with  the  different  kinds  of  fibres. 

COTTON  BLEACHING 

Cotton  is  commonly  bleached  in  the  yarn  or  woven  piece,  since 
there  is  no  special  demand  for  bleached  cotton-wool. 

Yarn  bleaching.  —  If  the  cotton  is  to  be  dyed  in  dark  colors,  it  is 
customary  to  give  it  a  thorough  boiling  in  water  alone,  or  with  the 


502  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

addition  of  some  soda-ash,  to  remove  the  grease,  wax,  and  resinous 
matters.  After  washing,  it  is  at  once  dyed.  But  for  white  yarn,  or 
that  to  be  dyed  any  light  shade,  the  bleaching  process  is  more  com- 
plicated. The  hanks  of  yarn  are  linked  together  to  form  a  chain, 
and  then  loosely  packed  into  a  closed  iron  vessel,  called  a  "  kier," 
where  they  are  boiled  for  several  hours  with  caustic  soda  or  soda-ash, 
under  a  low  pressure  (5  pounds  per  square  inch),  or  even  in  open 
vessels.  The  kier  has  a  false  bottom,  upon  which  the  yarn  rests.  A 
vertical  pipe  passes  up  through  the  centre  of  the  kier,  to  within  a  few 
inches  of  the  top.  Across  the  upper  end  of  this  pipe  is  a  dome-shaped 
bonnet,  and  at  the  lower  end  is  a  steam  injector  which  forces  the 
liquor  collected  under  the  false  bottom  up  through  the  pipe  against 
the  bonnet,  which  distributes  it  over  the  yarn,  through  which  it  per- 
colates, collecting  under  the  false  bottom.  Thus  a  constant  circula- 
tion of  the  liquor  is  maintained  in  the  kier.  On  an  average  about  4 
per  cent  (of  the  weight  of  the  goods)  of  soda-ash  is  used  in  the  lye. 

The  yarn  is  then  washed  with  clean  water  and  is  treated  with  a 
cold  dilute  bleaching  powder  solution,  called  the  "  chemick."  This 
is  about  2°  Tw.,  and  is  pumped  over  the  yarn  as  it  lies  in  a  wooden 
tank  having  a  false  bottom.  After  5  or  6  hours  the  yarn  is  removed, 
squeezed,  and  washed  in  water  for  a  few  minutes.  It  is  then  "  soured  " 
by  plunging  into  a  tank  containing  a  dilute  sulphuric  or  hydrochloric 
acid  of  about  1°  Tw.  Chlorine  is  thus  liberated  from  the  bleach 
absorbed  in  the  fibre,  and  sets  free  oxygen  from  the  water,  which  at 
once  attacks  and  destroys  the  coloring  matters,  the  yarn  becoming 
pure  white.  This  process  requires  about  15  to  20  minutes ;  then  the 
yarn  is  thoroughly  washed  in  water  and  passed  into  a  hot  soap  solu- 
tion, to  which  a  little  bluing  (ultramarine)  has  been  added,  if  the  yarn 
is  to  be  sold  uncolored.  The  soap  is  worked  into  the  yarn  by  squeeze- 
rolls,  until  the  fibres  are  uniformly  blued ;  then  the  excess  of  soapy 
water  is  removed  in  a  centrifugal  machine,  and  the  yarn  is  dried. 

The  Haubold  machine  for  yarn  washing  consists  of  a  circular  tub 
containing  a  rotating  central  shaft  from  which  square  bobbins  radiate. 
On  these  the  hanks  are  hung,  and  as  they  are  carried  slowly  forward, 
a  suitable  gearing  imparts  to  the  bobbins  an  intermittent  forward 
and  backward  rotation  on  their  own  axes.  The  tank  is  divided  by  a 
radial  partition,  on  one  side  of  which  fresh  water  enters,  while  on  the 
other  the  dirty  water  flows  out.  The  hanks  are  moved  against  the 
current  of  water,  and  are  taken  out  when  they  come  to  the  partition 
on  the  side  where  the  clean  water  enters. 

In  other  washing  machines,  the  yarn  is  pounded  by  heavy  wooden 


TEXTILE    INDUSTRIES 


503 


hammers  driven  by  power.  Or,  as  shown  in  Fig.  119,  the  hanks  tied 
together  to  form  a  chain  are  washed  by  passing  through  squeeze-rolls 
(A,  A)  and  under  a  stretching  roller  (B),  placed  in  the  bottom  of  the 
wash  tank.  The  yarn 
thus  passes  down  and 
up  under  the  rollers  and 
between  the  squeeze- 
rolls  several  times. 

Improved  apparatus 
is  now  employed,  in 
which  the  lye-boiling, 
chemicking,  souring, 
and  washing  are  all 
carried  on  in  one 
wooden  vessel.  The 

yarn  is  not  moved  dur-  FIQ  119 

ing    the    process,    and 

the  various  liquors  are  pumped  through  the  apparatus  in  their  order, 
and  the  labor  is  thus  much  reduced. 

Cloth  bleaching  is  done  by  one  of  three  methods:  the  market 
bleach  for  goods  to  be  sold  as  white  muslin ;  the  Turkey-red  bleach, 
for  goods  to  be  dyed  red  with  alizarin ;  the  madder  bleach  designed 
for  cloth  which  is  to  be  printed  with  various  mordants  and  then 
dyed  in  a  bath  of  alizarin.  The  latter  leaves  the  cotton  white  and 
almost  pure  cellulose.  It  is  necessary  to  remove  every  impurity 
which  can  attract  the  dye  or  prevent  its  taking  the  fibre.  If  the 
cotton  is  not  chemically  clean  before  printing,  the  pattern  will  not  be 
clear  and  sharp,  nor  the  background  a  pure  white. 

The  madder  bleach  is  carried  out  as  follows :  The  separate  pieces 
of  goods  are  marked  on  the  ends  for  future  identification,  and  then 
stitched  together,  end  to  end,  to  form  a  continuous  web,  which  is 
first  "  singed  "  to  remove  the  lint,  floss,  and  loose  hairs,  as  these  would 
prevent  the  printing  of  sharp  designs.  This  may  be  done  by  passing 
the  cloth,  opened  to  its  full  width,  over  one  or  two  red-hot  copper 
plates,  slightly  curved  and  set  in  the  roof  of  a  furnace ;  it  is  difficult 
to  keep  these  evenly  heated,  owing  to  the  cooling  effect  of  the  rapidly 
moving  cloth,  and  the  singeing  is  liable  to  be  imperfect  in  places. 
Consequently  a  revolving  hollow  roll  is  sometimes  used,  which  is  kept 
red  hot  by  passing  the  flames  of  the  furnace  through  it  on  their  way 
to  the  chimney.  Or  the  cloth  may  be  passed  over  a  row  of  Bunsen 
gas  flames.  Directly  over  these  is  a  small  roller,  under  which  the 


504 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


cloth  passes  at  sufficient  tension  to  cause  the  "nap  "  to  stand  out  well 
as  it  comes  into  the  flame.  As  soon  as  the  cloth  passes  the  hot  plate 
or  flame  it  is  plunged  into  a  trough  of  water,  to  extinguish  any  sparks. 
The  goods  are  then  thoroughly  wet  in  water  (the  "  gray-wash  "), 
and  much  of  the  sizing  and  dirt  is  removed.  The  cloth  is  then  usually 
piled  in  a  heap  and  left  overnight,  to  thoroughly  soften  the  gums  and 
starchy  matters  left  in  it.  It  is  then  given  the  "  lime-boil,"  with 
milk  of  lime  under  pressure  preferably  in  the  injector  kier.  The 
cloth  is  passed  through  a  trough  of  milk  of  lime,  of  which  it  absorbs 
about  4  or  5  per  cent  of  its  own  weight.  Without  wringing,  it  is 
passed  into  the  kier,  which  is  filled  nearly  full,  and  packed  by  boys, 
who  tread  the  cloth  down  evenly,  so  that  the  liquor  will  be  forced  to 
pass  through  it,  and  not  through  channels  between  the  folds.  Water 
is  introduced,  and  then  steam  is  blown  in  until  the  air  is  expelled  and 
the  kier  is  hot,  when  the  cover  is  screwed  down  and  the  boiling  con- 
tinued under  from  10  to  70  pounds  pressure,  for  several  hours.  The 
kier  (Fig.  120*)  is  made  of  boiler  plate,  and  is  from  6  to  10  feet  high 

by  4  to  6  feet  in  diameter;   it  will  hold 
from  600  to  3500  pounds  of  cloth.     Steam 
is    admitted   through    (A),   and  passing 
the  injector   (G),   draws  the  limewater 
through  (B)  and  delivers  it  through  (C) 
to  the  nozzle  (N),  which  sprays  it  over 
the  goods.     The  pressure  in  the  upper 
part  of  the  kier  forces  the  liquor  through 
the  goods,  and  it  collects  among  quartz 
pebbles    in    the    bottom,    whence   it   is 
drawn  through  (B)  to  the  top  of  the  kier. 
If   needed,  water  is   admitted   through 
(D)  and  milk  of  lime  through  (E).     At 
the  end  of  the  operation  the  waste  liquor 
is  drawn  off  through  (F). 
The  object  of  this  lime-boil  is  to  convert  the  fatty  matters  into 
lime  soap,  to  dissolve  the  starch  and  other  soluble  substances,  and  to 
so  change  the  natural  impurities  chemically,  that  they,  together  with 
the  lime  soap  formed,  are  readily  removed  in  succeeding  operations. 
The  cloth  is  usually  darker  after  this  treatment  than  before.     It 
is  next  washed  in  machines  similar  to  that  shown  in  Fig.  119,  to  re- 
move excess  lime,  soluble  matters,  and  loose  dirt.     The  rope  of  cloth 
is  thus  passed  through  the  water  and  between  the  rolls  (A,  A)  several 
*  After  Knecht,  Rawson,  and  Loewenthal,  Manual  of  Dyeing. 


FIG.  120. 


TEXTILE   INDUSTRIES  505 

times,  while  it  is  sprayed  by  a  heavy  stream  of  water  from  the  pipe 
(C)  as  it  comes  up  to  the  squeeze-rolls. 

It  now  passes  to  the  first-sour,  or  gray-sour,  where  it  is  treated 
with  dilute  sulphuric  or  hydrochloric  acid  at  1°  or  2°  Tw. ;  this  de- 
composes the  lime  soap,  and  removes  any  iron  stains  and  other  metallic 
oxides.  The  goods  are  then  passed  through  squeeze-rolls,  to  remove 
the  excess  of  acid,  and  are  thoroughly  washed  to  prevent  the  acid 
from  rotting  the  fibre,  as  it  would  on  long  exposure  to  the  air. 

The  lye-boils,  of  which  there  are  two  or  three,  are  also  carried  on 
in  the  injector  kier.  In  the  first  boiling  the  goods  are  treated  with 
1  per  cent  soda-ash  *  for  about  3  hours ;  in  the  second  about  3.6  per 
cent  soda-ash,  0.8  per  cent  caustic  soda,  and  1.6  per  cent  of  rosin  are 
used,  and  the  whole  boiled  for  12  hours;  the  third  lye-boil  is  with 
soda-ash  alone,  and  continues  for  3  hours.  These  boilings  remove 
the  remaining  fats  and  oils  from  the  lime  soaps,  and  extract  much  of 
the  brown  coloring  matter.  The  addition  of  rosin  is  a  characteristic 
of  the  madder  bleach,  and  is  supposed  to  remove  certain  substances 
from  the  cotton  which  readily  attract  the  dye. 

After  a  thorough  washing,  the  next  process  is  the  "  chemicking," 
or  treatment  with  bleaching  powder,  which  is  done  in  a  machine 
similar  to  the  squeeze-rolls  used  in  the  souring.  The  cloth  while 
still  wet  is  passed  through  a  clear,  cold  solution  of  bleaching  powder 
at  |°  to  2°  Tw.  It  is  then  piled  in  a  heap  and  left  for  some  hours. 
The  bleach  is  partly  decomposed  by  the  carbon  dioxide  of  the  air, 
and  hypochlorous  acid  is  set  free;  this  decomposes  in  the  presence 
of  organic  coloring  matter,  liberating  oxygen,  which  destroys  the 
color.  If  the  bleach  liquor  is  too  strong  the  cotton  is  attacked  and 
oxycellulose  formed,  which  is  objectionable. 

After  the  chemick,  the  cloth  is  piled  for  a  few  hours ;  then  it  is 
next  subjected  to  the  "  white-sour."  It  is  treated  with  dilute  mineral 
acid,  to  complete  the  liberation  of  chlorine  from  the  bleach  remaining 
in  the  fibre.  Hydrochloric  acid  is  the  best  for  this,  since  it  renders 
the  lime  more  soluble.  The  cotton  is  completely  decolorized,  and 
after  about  three  hours  is  thoroughly  washed.  It  is  passed  through 
squeeze-rolls,  and  then  opened  out  smooth  and  passed  over  large  cop- 
per drums,  heated  by  steam,  to  dry  it  thoroughly.  The  whole  time 
necessary  for  the  madder  bleach  is  about  five  days. 

For  24,000  kilos  of  cloth  the  following  scheme  is  given  by  Hum- 
nielrf  — 

*  These  percentages  are  calculated  on  the  weight  of  the  goods, 
t  Dyeing  of  Textile  Fabrics,  p.  77. 


506  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

1.  Wash  after  singeing. 

2.  Lime-boil :   1000  kilos  lime ;  boil  12  hours  ;   wash. 

3.  Lime-sour :   hydrochloric  acid,  2°  Tw. ;   wash. 

4.  Lye-boils :  — 

1st :  340  kilos  soda-ash  (If  per  cent  ash) :  boil  3  hours. 

2d :  860  kilos  soda-ash  ( =  3.6  per  cent).  ]  Boil 

380  kilos  rosin  (=1.6  per  cent).  >  12 

190  kilos  solid  caustic  soda  ( =  0.8  per  cent).  J  hours. 

3d:  380  kilos  soda-ash  (=  1.6  per  cent) ;  boil  3  hours;  wash. 

5.  Chemicking  :  bleaching  powder  solution,  J°  to  J°  Tw. ;  wash. 

6.  White-sour:   hydrochloric  acid,  2°  Tw. ;  pile  1  to  3  hours. 

7.  Wash,  squeeze,  and  dry. 

The  Turkey-red  bleach  is  employed  for  cotton  which  is  to  be 
dyed  a  full  color  with  alizarin  red.  It  is  essential  that  the  fibre  shall 
not  be  singed  nor  exposed  to  chlorine,*  since  the  development  of  a 
brilliant  red  would  be  thus  prevented.  The  process  is  therefore 
simpler,  the  outline  for  2000  kilos  of  cloth  being  as  follows :  f  — 

1.  Wash. 

2.  Boil  2  hours  in  water ;  wash. 

3.  Lye-boils :  — 

1st :  90  liters  of  caustic  soda  solution,  70°  Tw.  ( =  4j  per 
cent  of  weight  of  goods) ;  boil  10  hours ;  wash. 

2d:  70  liters  of  caustic  soda  solution,  70°  Tw.  (=  3J  per 
cent  of  weight  of  goods) ;  boil  10  hours ;  wash. 

4.  Sour :   sulphuric  acid,  2°  Tw. ;  steep  2  hours. 

5.  Wash  well,  and  dry. 

The  market  bleach  differs  from  the  madder  bleach  chiefly  in  that 
the  singeing  and  rosin-boil  are  omitted  and  the  cloth  is  starched  and 
blued  slightly  before  drying.  An  outline  of  the  process  is  about  as 
follows :  — 

1.  Gray-wash. 

2.  Lime-boil :   8  to  12  hours ;   wash. 

3.  Lime-sour :    hydrochloric  acid,  2°  Tw. ;    steep  2   to  4   hours ; 

wash  well. 

*  The  injurious  action  of  the  chlorine  is  supposed  to  be  due  to  the  formation  of 
oxycellulose.     J.  Soc.  Dyers  and  Colorists,  1886,  29. 
t  Hummel,  Dyeing  of  Textile  Fabrics,  p.  85. 


TEXTILE   INDUSTRIES  507 

4.  Lye-boils :  — 

1st :   1|  to  3  per  cent  soda-ash ;  boil  3  to  12  hours. 
2d:    1J  to  3  per  cent  spda-ash;    boil  3  to  12  hours;    wash 
well. 

5.  Chemick :   bleaching  powder  solution,  J°  to  J°  Tw. ;   pile  6  to 

12  hours. 

6.  White-sour :  hydrochloric  acid,  2°  Tw. ;  pile  3  hours ;  wash. 

7.  Starched  and  blued. 

8.  Calendered. 

9.  Tentered  and  folded. 

Much  care  is  taken  in  the  finishing  operations.  The  bluing  is 
generally  mixed  with  the  boiled  starch,  and  after  passing  through 
squeeze-rolls,  the  lightly  starched  cloth  goes  to  the  calender  ma- 
chine. Here  it  is  heavily  pressed  between  hot,  polished  steel  rolls 
to  give  it  a  smooth  and  glossy  surface.  Next  it  goes  to  the  tenter- 
ing  machine,  which  consists  of  a  travelling  frame  with  parallel  sides, 
carrying  clips  or  hooks,  to  which  the  cloth  is  fastened  by  the  selvedges. 
The  side  rods  of  the  frame  have  an  intermittent  backward  and  forward 
movement  which  stretches  and  draws  the  cloth  in  the  direction  of 
its  width.  Beneath  are  a  number  of  flat  steam-boxes,  the  heat  from 
which  rapidly  dries  the  cloth.  Finally,  it  goes  to  a  folding  machine, 
by  which  the  cloth  is  laid  in  folds  one  yard  in  length;  the  number 
of  yards  required  for  a  bolt  is  then  cut  off. 

Various  modified  bleaching  processes  have  been  devised,  chiefly 
with  the  view  of  saving  time,  labor,  and  wear  on  the  goods.  That 
of  Horace  Koechlin  has  been  introduced  in  some  works.  The  lime- 
boil  is  abolished,  and  a  single  caustic  soda  and  rosin-boil  is  substi- 
tuted for  the  lye-boils.  A  special  horizontal  kier  is  used,  into  which 
cars  packed  with  the  cloth  can  be  run.  The  boiling  here  is  not 
essentially  different  from  that  in  the  ordinary  form,  but  the  cars 
are  run  out  and  others  immediately  run  in,  without  material  cooling 
of  the  kier ;  thus  much  time  is  saved.  The  chemicking,  souring,  and 
washing  are  carried  on  in  the  usual  way. 

In  the  Mather-Thompson  process  *  the  same  kier  is  used  as  in  the 
Koechlin  process,  but  a  special  apparatus  is  employed  for  the  sub- 
sequent chemicking,  followed  by  a  soda-boil  and  a  second  chemicking. 
After  passing  through  the  bleaching  powder  solution  the  cloth  is 
exposed  to  the  action  of  carbon  dioxide  gas  to  set  free  the  hypochlorous 
acid  ;  this  hastens  the  bleaching. 

*  For  details  of  this  process,  see  Thorpe's  Dictionary  of  Applied  Chemistry 
(Revised  Ed.),  Vol.  I,  472. 


508  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

The  Hermite  bleaching  process  *  depends  upon  the  electrolytic 
decomposition  of  magnesium  or  aluminum  chloride,  to  form  bleach 
liquors  consisting  of  hypochlorites  of  these  metals ;  the  liquors  are 
employed  instead  of  bleaching  powder  for  chemicking. 

Peroxide  of  hydrogen  used  in  conjunction  with  soap,  magnesia, 
and  caustic  soda  in  a  boiling  bath  gives  an  excellent  bleach  on  cotton. 
But  its  cost  is  yet  too  great  to  allow  of  its  general  use  for  this 
purpose. 

Permanganate  of  potassium,  in  slightly  acid  solution,  gives  a 
very  good  bleach  on  cotton  which  has  been  boiled  in  caustic  soda  to 
remove  gums  and  oily  matters.  Alkaline  permanganate  must  be 
avoided,  as  it  forms  oxy cellulose.  When  removed  from  the  perman- 
ganate bath,  the  goods  are  colored  a  deep  brown,  but  a  pure  white 
is  produced  by  passing  them  into  a  bath  of  sodium  bisulphite  or 
sulphurous  acid.  The  process  is  worked  cold  and  the  goods  must 
be  thoroughly  washed  after  bleaching. 

LINEN  BLEACHING 

Linen  contains  more  than  25  per  cent  coloring  matter  and  other 
impurities  (chiefly  pectic  acid,  so-called),  and  the  bleaching  process 
is  more  difficult  and  tedious,  although  essentially  similar  to  that  used 
for  cotton.  Linen  is  more  readily  attacked  by  alkalies,  acids,  or 
chlorine,  and  more  care  and  time  (from  3  to  6  weeks)  are  needed 
to  prevent  injury  to  the  fibre.  The  liquors  are  much  weaker  and  the 
processes  are  usually  repeated  several  times.  It  is  also  customary 
to  "  grass  "  linen  for  a  week ;  i.e.  to  expose  it  to  the  sun  and  dew  by 
spreading  it  on  the  grass.  It  is  frequently  moistened  to  assist  in  the 
bleaching.  It  is  supposed  that  the  ozone  in  the  air  is  here  the  active 
agent. 

Linen  is  bleached  in  the  form  of  thread,  yarn,  or  cloth.  According 
to  the  degree  of  whiteness,  it  is  said  to  be  quarter,  half,  or  three- 
quarters  bleached,  but  the  strength  of  the  fibre  diminishes  as  the 
purity  of  the  white  increases.  The  following  outline  of  the  Irish 
process  for  yarn  bleaching  is  according  to  Hummel  f  :  — 

1.  Lye-boil :    10  per  cent  soda-ash  in  solution,  boil  3  to  4  hours, 

wash  and  squeeze. 

2.  Chemick:    reel  one  hour  in  bleaching  powder  solution  at  |° 

Tw. ;  wash. 

3.  Sour :  steep  one  hour  in  sulphuric  acid  at  1°  Tw. ;  wash. 

*  Hurter,  J.  Soc.  Chem.  Ind.,  1887,  337. 

t  Hummel,  Dyeing  of  Textile  Fabrics,  p.  88. 


TEXTILE    INDUSTRIES  509 

4.  Lye-boil  (scald) :   boil  one  hour  with  2  to  5  per  cent  soda-ash 

in  solution ;  wash. 

5.  Chemick  :  reel  again  as  in  (2) ;  wash. 

6.  Sour,  as  in  (3) ;  wash  well  and  dry. 

This  gives  a  half  bleach ;  for  three-quarters  bleach,  repeat  Nos.  4, 
5,  and  6,  but  after  the  lye-boil  (4),  grass  for  a  week ;  and  in  (5),  in- 
stead of  reeling  the  yarn,  steep  it  in  the  bleach  liquor  10  to  12  hours. 

Linen  piece  goods*  are  bleached  similarly  to  cotton  cloth,  but 
the  details  vary.  There  are  the  same  lime-boil,  sour,  and  several  lye- 
boils  with  caustic  soda,  then  a  grassing  for  several  days,  followed  by  a 
chemick,  sour,  and  third  soda-boil,  another  grassing,  and  a  second 
chemick.  If  not  white,  the  goods  are  rubbed  between  rubbing  boards 
with  a  strong  soap  solution,  to  remove  mechanically  the  fine  black 
specks  called  "  sprits  "  adhering  to  the  fibre.  This  is  followed  by  a 
third  grassing,  chemick,  sour,  and  washing. 

Potassium  permanganate  has  been  recommended  for  linen  bleach- 
ing in  conjunction  with  sulphurous  acid  or  hydrogen  peroxide.  These 
substances  act  rapidly  and  reduce  the  time  o£  bleaching  to  a  few  days. 

Jute  is  bleached  by  treatment  with  sodium  hypochlorite  or  bleach- 
ing powder  solution,  followed  by  a  sour  and  thorough  washing. 
Sodium  hypochlorite  liquor  containing  about  1  per  cent  of  available 
chlorine  is  recommended  for  cloth,  the  presence  of  the  soda  prevent- 
ing the  formation  of  chlorinated  products.  Yarn  is  commonly  treated 
with  bleaching  powder  solution,  three  baths  being  used ;  these  vary 
in  concentration  from  about  20  per  cent  (on  the  weight  of  the  goods), 
down  to  5  per  cent  of  bleaching  powder  in  the  last  bath.  The  yarn 
is  hung  in  each  bath  for  half  an  hour  or  more,  at  a  temperature  of 
48°  C. ;  it  is  then  washed,  treated  with  sulphuric  acid  at  1°  Tw.  for  half 
an  hour,  again  washed  and  dried.  (In  the  presence  of  water,  chlorine 
may  combine  with  the  jute,  forming  yellow  chlorination  products.) 

Potassium  permanganate,  followed  by  treatment  with  sulphurous 
acid,  yields  a  good  bleach  but  is  expensive;  sodium  peroxide  also 
gives  a  good  bleach  and  is  used  to  some  extent. 

Hemp  is  not  often  bleached,  since  its  chief  use  is  for  cordage  and 
twine,  where  the  color  is  of  no  consequence.  It  is  sometimes  par- 
tially bleached  by  boiling  in  sodium  silicate,  washing  and  treating 
with  bleaching  powder  solution  for  some  hours,  then  souring  in  dilute 
acid  and  washing  thoroughly. 

*  Herzfeld,  Handbuch  der  Farberei,  p.  375.     Also  see  Hummel. 


510  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


WOOL  BLEACHING 

The  preliminary  operations  of  washing  and  scouring  the  loose 
wool  have  already  been  described  on  p.  499.  After  spinning,  the 
yarn  is  left  greasy,  and  a  second  scouring  is  necessary  before  bleaching 
or  dyeing. 

Wool  yarn,  especially  when  tightly  twisted,  shows  a  decided  ten- 
dency to  curl  and  shrink  when  wet  in  warm  water.  As  this  would 
cause  tangles  and  felting  in  the  scouring  and  dyeing,  the  yarn  is 
stretched  on  a  strong  frame  carrying  a  number  of  projecting  arms. 
A  hank  of  yarn  is  hung  over  two  of  these  arms,  and  is  stretched  tight 
by  means  of  screws  which  separate  the  arms.  When  filled,  the  frame 
is  submerged  in  boiling  water  for  half  an  hour.  It  is  then  taken  out, 
and  the  yarn  allowed  to  cool  while  stretched.  The  hanks  are  then 
shifted  so  that  the  portion  that  was  in  contact  with  the  arms  now  comes 
between  them,  and  the  entire  process  repeated.  This  removes  all  the 
"  curl,"  and  the  yarn  is  ready  for  scouring,  which  may  be  done  by 
hand  or  in  machines.  In  the  first  method,  the  hanks  are  suspended 
from  wooden  rods  in  the  tank  containing  the  hot  scouring  liquor  (soap 
solution),  and  are  swung  to  and  fro,  with  frequent  turning  of  the  rod, 
to  wet  all  parts  of  the  hank.  They  are  then  washed  by  swinging  them 
in  a  tank  of  water.  An  effective  scouring  machine  for  yarn  consists  of 
a  pair  of  squeeze-rolls  placed  over  a  tank  filled  with  soap  liquor,  and 
containing  several  rollers,  under  and  over  which  the  hanks,  tied  to- 
gether in  a  chain,  are  passed. 

Woolen  cloth  may  be  scoured  in  a  scouring  machine  called  a 
"  dolly  "  ;  the  cloth  is  passed  as  a  rope  through  the  soap  liquor,  and 
then  between  squeeze-rolls.  But  goods  which  are  liable  to  crease 
must  be  scoured  in  the  open-  width  scouring  machine.  The  cloth  is 
then  sprayed  with  clean  water,  returned  to  the  soap  bath,  and  again 
put  through  the  squeeze-rolls.  The  dirty  soap  liquor  expressed  is 
caught  in  a  special  trough,  and  is  run  off.  The  cloth  is  finally  washed 
with  water  to  remove  all  the  soap. 

Mixed  goods,  called  "  unions,"  composed  of  cotton  warp  and  wool 
weft,  or  goods  made  of  two  kinds  of  wool,  will  "  cockle  "  or  wrinkle 
when  wet,  owing  to  unequal  shrinkage.  They  are  consequently 
"  crabbed,"  to  take  the  stretch  out  of  the  fibre.  The  cloth  is  passed 
through  a  bath  of  boiling  water,  and  at  once  rolled  tight  and  smooth 
on  a  roller  or  beam.  After  cooling  on  the  roll,  it  is  again  passed  through 
hot  water,  and  rewound  on  a  second  beam.  The  process  is  repeated 
a  third  time,  using  cold  water,  and  rolling  the  cloth  under  heavy 


TEXTILE    INDUSTRIES  511 

pressure,  obtained  by  a  weighted  roller  resting  on  top  of  the  beam. 
In  order  to  stretch  the  goods  under  higher  temperatures  than  they 
will  be  subjected  to  in  the  subsequent  dyeing,  they  are  next  steamed 
by  rolling  them  on  a  perforated  iron  cylinder,  into  which  steam  at 
40  pounds  pressure  is  admitted  and  forced  through  the  whole  thick- 
ness of  the  cloth.  After  cooling,  it  is  rewound  on  another  perforated 
roll,  and  steamed  again.  This  rewinding  brings  those  portions  of 
the  cloth  which  were  on  the  outside  of  the  roll  into  the  centre  and 
nearer  the  steam  entrance,  so  that  the  effect  of  the  high  temperature 
is  made  more  even  throughout  the  piece.  The  goods  may  now  be 
scoured  and  dyed  without  shrinkage,  provided  that  the  temperature 
in  these  processes  does  not  exceed  that  obtained  in  the  crabbing 
and  steaming. 

Wool  cannot  be  bleached  by  any  process  similar  to  that  used  for 
vegetable  fibre,  since  it  would  be  dissolved  by  the  lye-boils,  while 
chlorine  would  combine  with  the  fibre  without  destroying  the  natural 
yellow  color.  The  bleaching  agent  most  generally  used  is  sulphur 
dioxide,  or  its  solution  in  water  as  sulphurous  acid.  It  is  almost 
always  used  as  gas,  and  the  operation  is  called  "  stoving,"  sulphur- 
ing, or  gas  bleaching.  It  is  carried  on  in  a  closed  brick  chamber,  or 
"  stove,"  about  6  X  10  X  6  feet,  the  wooden  lining  of  which  is  made 
fast  by  wooden  pegs,  so  that  all  metal  (especially  iron)  is  excluded. 
The  washed  and  scoured  hanks  are  hung  on  wooden  rods,  for  6  or  8 
hours,  in  contact  with  the  sulphur  fumes  produced  by  burning  sul- 
phur in  a  pot  in  the  bottom  of  the  stove.  Thin  cloth  is  stoved  by 
passing  it,  in  the  open  width,  in  a  zigzag  course  up  and  down  many 
times  over  rollers  at  the  top  and  bottom  of  the  chamber,  which  it 
finally  leaves  through  the  same  narrow  slit  at  which  it  enters.  It 
may  be  passed  through  the  chamber  several  times,  until  sufficiently 
bleached. 

Sometimes  the  goods  are  soaked  for  24  hours  in  a  solution  of 
sulphurous  acid,  or  sodium  bisulphite  with  mineral  acid,  and  then 
wrung  and  washed. 

The  action  of  sulphur  compounds  in  bleaching  wool  is  not  entirely 
clear.  By  some  authorities,  the  sulphur  is  supposed  to  decompose 
the  water  present,  liberating  hydrogen,  which,  in  turn,  unites  with 
the  color  to  form  a  colorless  body.  By  others  it  is  thought  that  the 
sulphur  enters  into  combination  with  the  coloring  matter  to  form  a 
colorless  sulphite  compound.  But  whatever  the  actual  reaction,  the 
bleach  is  not  permanent,  and  after  some  time  the  yellow  color  gradu- 
ally returns,  especially  if  the  goods  are  washed  with  soap  or  alkalies. 


512  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

Hydrogen  peroxide  is  an  effective  but  expensive  bleaching  agent 
for  wool.  Since  it  affords  a  permanent  bleach,  the  coloring  matter 
is  probably  oxidized  and  destroyed.  The  goods  are  soaked  at  15°  C. 
for  24  hours  in  a  3  per  cent  solution  of  hydrogen  peroxide,  contain- 
ing 2  per  cent  of  ammonia  (sp.  gr.  0.910).  Increasing  the  temper- 
ature hastens  the  process.  Hydrogen  peroxide  is  also  used  for 
bleaching  hair,  furs,  and  feathers. 

SILK  BLEACHING 

The  boiling  off  and  discharging  of  raw  silk  has  already  been  con- 
sidered (p.  494).  It  is  often  subjected  to  various  mechanical  treat- 
ments to  increase  its  lustre,  e.g.  "  stretching,"  in  which  the  hanks 
are  given  a  series  of  violent  jerks  while  suspended  from  a  fixed  peg ; 
"  glossing,"  in  which  they  are  twisted  very  tight ;  or  "  lustreing," 
by  steaming  them  while  in  a  state  of  great  tension. 

Silk  is  bleached  with  sulphur  dioxide,  or  with  hydrogen  peroxide, 
or  with  potassium  permanganate  and  sulphurous  acid.  The  stoving 
process,  similar  to  that  used  for  wool  bleaching,  is  repeated  several 
times,  the  silk  being  washed  after  each  stoving.  It  is  then  tinted 
with  a  trace  of  some  blue  or  other  coal-tar  dye  to  make  it  appear  a 
clearer  white. 

Tussah  silk  is  hard  to  bleach,  and  cannot  be  decolorized  by  stov- 
ing. A  bath  of  barium  peroxide  in  water,  followed  by  dilute  hydro- 
chloric acid,  is  recommended  by  Tessie  du  Motay.  Ammoniacal 
hydrogen  peroxide  may  also  act  on  silk  as  on  wool.  But,  at  best, 
tussah  silk  can  only  be  bleached  a  light  cream  color. 

MORDANTS 

A  moidant  is  a  substance  used  in  textile  dyeing  and  printing, 
either  to  fix  or  to  develop  the  color  on  the  fibre.  In  the  firs^t  case,  it 
combines  with  the  fibre,  and  forms  a  body  having  affinity  for  color- 
ing matter ;  in  the  second,  it  becomes  an  essential  constituent  of  the 
color  when  deposited  on  the  fibre.  Metallic  mordants  are  abstracted 
from  aqueous  solution,  wholly  or  in  part,  by  the  fibre,  upon  which 
they  generally  deposit  metallic  hydroxides  or  basic  salts,  which  form 
color  lakes  in  the  dyeing  process. 

Mordants  are  either  of  mineral  or  of  organic  origin.  The  former 
comprise  the  common  mineral  acids,  and  salts  of  aluminum,  chro- 
mium, iron,  copper,  antimony,  and  tin,  and  to  a  lesser  degree  those  of 
manganese,  cobalt,  nickel,  uranium,  vanadium,  and  tungsten.  The 


TEXTILE    INDUSTRIES  513 

organic  mordants  are  certain  organic  acids,  especially  acetic,  oxalic, 
tartaric,  citric,  lactic,  the  sulphated  ricinoleic  and  oleic  acids  forming 
Turkey-red  oil,  and  tannin  substances,  mainly  derivatives  of  gallic 
or  protocatechuic  acids.  Only  the  most  important  of  these  mordants 
can  be  mentioned  here. 

Aluminum  mordants  are  chiefly  the  acetate  or  "  red  liquor " 
(p.  308),  sulphate  (p.  282),  and  the  alums  (p.  285).  The  chlorides 
and  nitrates  are  rarely  used.  Aluminum  salts  are  used  for  mor- 
danting cotton,  linen,  and  wool,  but  seldom  for  silk.  Alum  and 
normal  sulphate  do  not  readily  yield  alumina  to  cotton.  Basic 
sulphates  are  generally  used,  and  deposit  over  50  per  cent  of  their 
alumina  on  the  fibre,  when  it  is  steeped  in  them,  and  then  dried  and 
aged  in  a  warm  atmosphere.  Sometimes  the  fibre  is  first  soaked  in 
some  such  substance  as  tannic  acid,  Turkey-red  oil,  or  stannate  of 
soda,  which  forms  insoluble  compounds  with  the  alumina  of  the  basic 
sulphate,  or  precipitates  it  as  such  in  an  insoluble  form.  The  acetate 
is  only  used  for  Turkey-red,  and  the  alumina  is  fixed  by  the  evapora- 
tion of  acetic  acid  during  the  aging. 

Alum  and  neutral  sulphate  are  much  used  for  wool,  the  fibre 
decomposing  these  solutions  when  boiled  in  them,  and  retaining  the 
alumina  in  an  insoluble  form.  The  wool  fibre  is  both  acid  and  basic 
in  character,  dissociating  these  salts,  and  combining  with  both  the 
acid  and  the  base  of  the  salt.  This  reaction  is  most  complete  at  a 
boiling  temperature;  but  for  the  best  results  the  salts  must  not  be 
decomposed  until  they  have  had  time  to  penetrate  into  the  fibre. 
Decomposition  is  retarded  by  using  tartrates  or  oxalates  in  con- 
junction with  the  aluminum  sulphate*;  these  probably  form  alu- 
minum tartrate  or  oxalate  by  double  decomposition,  and  the  alu- 
minum is  slowly  given  up  to  the  fibre.  Acid  potassium  tartrate 
(cream  of  tartar)  has  the  best  effect,  but  free  sulphuric,  hydrochloric, 
or  oxalic  acids  also  retard  the  decomposition. 

Silk  is  very  seldom  mordanted  in  this  way,  as  the  lustre  would  be 
injured. 

Chromium  salts,  which  react  similarly  to  the  aluminum  salts,  are 
used  for  cotton,  linen,  and  wool.  With  these  are  included  the  chro- 
mates  and  bichromates,  but  in  all  cases  chromic  oxide,  Cr2O3,  is 
fixed  on  the  fibre.  Chromic  acid  and  its  salts  act  here  as  oxidiz- 
ing agents,  and  are  themselves  reduced  to  chromic  oxide  before 
deposition. 

Cotton  and  linen  are  difficult  to  impregnate  with  chromium  salts. 
The  sulphates,  nitrates,  and  acetates  are  much  used  in  calico  print- 

2L 


514  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

ing,  while  bichromates  and  alkaline  solutions  of  chromium  hydroxide 
are  used  in  dyeing  and  printing.  The  most  successful  method  of  mor- 
danting cotton  with  chromium  salts  is  that  proposed  by  H.  Koechlin. 
The  cotton  is  soaked  in  the  solution  of  chromium  salt  (preferably 
basic  salt),  dried  and  passed  through  boiling  soda  solution ;  the  pro- 
cess is  repeated  until  the  goods  are  sufficiently  mordanted. 

Another  process  is  to  prepare  the  goods  with  tannin,  or  with 
Turkey-red  oil,  and  then  soak  them  in  the  chromium  solution;  the 
fixing  is  done  in  cold  limewater.  A  solution  of  basic  chromium 
acetate  is  used  for  cotton ;  after  steeping  some  hours,  it  is  dried 
and  steamed  in  a  closed  chamber,  to  fix  the  chromium  oxide  on  the 
fibre. 

Wool  is  mordanted  with  chromium  fluoride,  chrome  alum,  or 
bichromate  (chromic  acid).  Chrome  alum  yields  the  largest  quan- 
tity of  chromium  to  the  fibre,  but  in  dyeing,  the  result  is  less  satis- 
factory than  with  bichromates.  The  addition  of  cream  of  tartar  to 
chrome  alum  is  an  improvement.  Chromium  fluoride  mordants  wool 
very  well,  being  easily  but  slowly  decomposed,  without  the  use  of 
tartrates.  A  little  oxalic  acid  is  generally  added.  The  chromic  acid 
thus  deposited  on  the  fibre  does  not  affect  the  feel  or  spinning  quali- 
ties of  the  wool,  while  the  hydrofluoric  acid  set  free  appears  to  have 
no  injurious  action  on  the  dye  or  goods. 

Potassium  bichromate  is  the  most  generally  useful  mordant  for 
"wool,  yielding  fast  and  brilliant  colors  on  dyeing.  The  mordant  bath 
contains  potassium  bichromate  to  the  amount  of  2  to  4  per  cent  of 
the  weight  of  the  wool,  dissolved  in  water  equal  to  50  to  100  times 
the  weight  of  the  wool.  The  goods  are  boiled  in  this  for  one  or  one 
and  a  half  hours,  and  washed,  and  are  then  ready  for  dyeing.  Sul- 
.  phuric  acid  is  sometimes  added  to  the  mordant  bath  in  small  amounts, 
but  better  results  are  obtained  with  oxalic  acid  or  cream  of  tartar, 
which  reduce  part  of  the  bichromate  to  chromium  hydroxide  on 
the  fibre;  by  treating  the  chromed  wool  in  a  bath  of  sodium  bisul- 
phite the  reduction  is  more  complete.  An  excess  of  chromic  acid 
in  the  fibre  oxidizes  the  color,  deadening  it  when  dyed,  and  also 
weakens  the  fibre.  Such  "  overchromed  "  wool  is  said  to  be  greatly 
improved  by  reduction  of  the  bichromate  in  the  fibre  before  dyeing. 

The  nature  of  the  changes  which  take  place  in  mordanting  wool 
with  bichromate  has  been  much  studied,  but  is  not  yet  clearly  proved. 
The  work  of  Knecht,*  and  of  Kay  and  Bastow,f  indicates  that  the 

*  Journal  of  the  Society  of  Dyers  and  Colorists,  1888,  104  ;    and  1889,  186. 
t  Ibid.,  1887,  118. 


TEXTILE    INDUSTRIES  515 

potassium  bichromate  is  partly  dissociated  into  neutral  chromate 
and  chromic  acid  :  — 

K2Cr2O7  =  K2CrO4  +  CrO3, 

the  latter  being  absorbed  by  the  fibre,  while  the  neutral  chromate 
remains  in  the  bath.  This  chromic  acid  is  subsequently  reduced 
during  the  dyeing. 

Silk  is  sometimes  mordanted  with  basic  chromium  salts,  and 
potassium  bichromate  is  occasionally  used  as  an  oxidizing  agent  in 
dyeing  catechu  browns  and  logwood  blacks. 

Iron  salts  are  largely  used,  both  in  dyeing  and  printing,  and  on 
all  fibres.  Both  ferrous  and  ferric  salts  are  employed,  the  mcst  im- 
portant being  sulphates,  basic  sulphates  (nitrate  of  iron),  acetates, 
and  nitrates.  They  are  not  only  applied  as  mordants,  but  also  as 
oxidizing  and  weighting  materials  to  modify  the  shades  of  color,  or  to 
increase  the  stiffness  and  density  of  the  goods.  With  most  dyes,  iron 
salts  tend  to  "  sadden  "  or  darken  the  shade,  and  are  therefore  chiefly 
used  for  dark  colors,  especially  browns  and  blacks.  In  mordanting, 
the  iron  is  usually  fixed  on  the  fibre  as  hydroxide  or  tannate. 

Cotton  is  treated  with  ferrous  sulphate  (copperas,  p.  279),  after 
having  been  previously  steeped  in  tannin,  thus  precipitating  tan- 
nate of  iron  on  the  fibre.  Ferrous  acetate  (pyrolignite  of  iron,  p.  309) 
is  used  by  impregnating  the  fibre  with  the  solution,  drying,  and 
aging,  or  the  goods  may  be  passed  through  limewater.  It  is  also 
used  with  tannin-prepared  cotton.  Nitrate  of  iron  (basic  sulphate, 
p.  148)  is  generally  used  for  cotton,  which  is  merely  saturated  in  the 
solution,  and  then  passed  into  limewater  or  sodium  carbonate  solu- 
tion, the  process  being  repeated  until  sufficient  hydroxide  has  been 
deposited  on  the  fibre.  Iron  buff  is  produced  in  this  way.  Some- 
times the  goods  are  prepared  with  tannin,  passed  through  the  lime- 
water  to  form  calcium  tannate,  and  then  into  the  iron  solution. 
This  produces  ferric  tannate,  varying  in  color  from  brown  to  black. 

Wool  is  sometimes  mordanted  by  boiling  with  oxalic  acid  and 
copperas,  the  latter  chiefly  to  sadden  the  color ;  but  other  iron  salts 
are  not  used. 

Silks  are  extensively  treated  with  iron  salts  in  dyeing  blacks. 
The  pyrolignite  of  iron  is  chiefly  used  on  raw  silks  which  have  been 
previously  prepared  with  tannin,  preferably  chestnut  extract.  The 
silk  is  worked  in  a  warm  (60°  C.)  pyrolignite  of  'iron  solution,  ex- 
posed to  the  air  for  a  short  time,  and  then  washed.  By  sufficient 
repetition  of  this  treatment  the  weight  can  be  increased  by  20  to 


516  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

150  per  cent  of  the  original  weight  of  the  silk.  Hard  water  greatly 
assists  this  process.  The  color  produced  is  a  bluish  black;  the  lus- 
tre is  dulled,  but  is  restored  by  a  bath  of  very  dilute  hydrochloric 
acid,  to  which  a  little  olive  oil  has  been  added. 

Boiled-off  silk  is  weighted  and  dyed  by  the  use  of  nitrate  of  iron, 
the  silk  being  worked  in  the  iron  liquor,  washed,  and  put  into  a  boil- 
ing soap  solution  composed  of  "  boiled-off  liquor  "  (p.  494),  olein 
soap,  and  a  little  soda  crystals.  This  precipitates  the  ferric  hydrox- 
ide. The  silk  is  then  washed  with  hard  water  (which  helps  fix  the 
iron),  and  the  whole  process  repeated  until  sufficient  iron  has  been 
deposited  on  the  fibre.  With  each  operation,  the  weight  of  the  silk 
is  increased  about  4  per  cent,  and  the  color  becomes  dark  brown, 
though  the  lustre  is  preserved.  This  weighted  and  mordanted  silk 
is  then  dyed  black. 

Raw  silk  is  also  weighted  with  nitrate  of  iron  and  has  greater 
affinity  for  the  iron  salt  than  has  boiled-off  silk. 

Copper  salts  are  chiefly  used  as  oxidizing  materials  in  mordant- 
ing, acting  as  carriers  of  oxygen.  Copper  sulphate  (blue  vitriol, 
p.  280)  and  acetate  (verdigris,  p.  237)  are  most  used. 

Copper  sulphate  is  used  in  producing  logwood  blacks  and  cutch 
browns  on  cotton.  On  wool,  it  is  used  together  with  aluminum  sul- 
phate and  copperas  for  logwood  blues  and  blacks,  and  also  with 
potassium  bichromate.  Copper  salts  act  as  saddeners  for  logwood 
blacks  on  silk. 

Antimony  salts  used  as  mordants  are  tartar  emetic  (potassium 
antimony  tartrate),  double  oxalates  of  potassium  and  antimony,  and 
fluorides  of  antimony  and  sodium.  They  are  always  used  after  tan- 
nin mordanting  on  vegetable  fibre,  where  they  form  antimony  tan- 
nates.  They  are  not  used  for  silk  or  wool.  Tartar  emetic  is 
generally  employed,  and  its  application  is  simple ;  the  tannin  mor- 
danted cotton  is  passed  at  once  into  a  cold  bath  of  the  salt,  and  then 
thoroughly  washed  before  drying. 

Tin  salts  are  valuable  mordants,  yielding  especially  brilliant 
shades.  The  salts  chiefly  used  are  stannous  chloride  (tin  crystals, 
SnCl2  •  2  H2O),  stannic  chloride,  SnCl4,  sodium  stannate  ("  preparing 
salt,"  Na2SnO3),  and  stannous  nitrate,  Sn(NO3)2  (known  only  in  solu- 
tion). "  Tin  spirits  "  is  a  general  name  for  a  number  of  tin  solutions 
of  various  composition,  made  with  nitric,  sulphuric,  or  oxalic  acid. 
By  dissolving  granulated  tin  in  concentrated  hydrochloric  acid,  a  so- 
lution of  stannous  chloride  is  formed,  which  is  sold  as  "  muriate  of 
tin  " ;  or  tin  crystals  are  separated  from  it,  and  the  mother-liquors, 


TEXTILE    INDUSTRIES  517 

containing  a  large  amount  of  tin  chloride,  are  often  sold  as  muriate 
of  tin,  single  or  double,  according  to  the  strength.  "  Pink  salt  "  is  a 
double  stannic-ammonium  chloride,  SnCl4  +  2  NHiCl,  formerly  much 
used  as  a  mordant.  Various  solutions  of  stannic  salts  were  much 
used  under  such  names  as  Cotton  Spirits,  Pink  Cutting  Liquor,  Oxy- 
muriate  of  Tin,  Solution  of  Tin,  etc. 

Cotton  and  linen  are  not  often  mordanted  with  stannous  salts, 
but  being  powerful  reducing  agents,  they  (especially  tin  crystals)  are 
used  by  the  calico  printer  in  "  discharges,"  or  "  resists."  Stannous 
chloride  reduces  iron  salts  and  is  used  to  neutralize  the  effect  of  iron 
impurities  in  calico  printing.  Stannic  salts  are  used  as  mordants  on 
cotton  and  linen,  when  these  are  dyed  with  natural  dye-stuffs,  such 
as  camwood,  barwood,  fustic,  etc.,  and  for  some  of  the  aniline  dyes. 
Tannic  acid  is  used  before  the  tin,  and  stannic  oxide  or  stannic  tan- 
nate  is  fixed  on  the  fibre.  Stannate  of  soda  is  also  used  to  mordant 
cotton  and  to  prepare  it  for  printing ;  the  goods  are  steeped  in  the 
solution  and  then  passed  into  a  bath  of  dilute  mineral  acid  or  alumi- 
num sulphate,  which  precipitates  stannic  hydroxide  on  the  fibre. 

Wool  is  often  mordanted  with  stannous  chloride  by  entering  it  in 
a  cold  bath  of  about  4  per  cent  tin  crystals  (calculated  on  the  weight 
of  the  wool)  and  2  per  cent  oxalic  acid  or  cream  of  tartar.  This  is 
then  slowly  heated  to  boiling.  Too  much  tin  salt  makes  the  wool 
harsh  and  prevents  proper  felting  in  the  milling  process.  Stannic 
chloride  is  not  a  suitable  mordant  for  wool,  but  impure  mixtures  of 
stannic  and  stannous  salts  are  often  used  as  mordants  for  cochineal 
scarlets  on  wool.  Wool  is  sometimes  prepared  with  sodium  stannate 
for  printing,  followed  by  treatment  with  dilute  sulphuric  acid. 

Black  silks  are  weighted  with  stannous  chloride  together  with 
catechu,  on  fibre  which  has  already  been  weighted  with  iron.  For 
weighting  light-colored  silks,  stannic  chloride  (tin  spirits)  is  often 
used.  The  raw  fibre  is  steeped  in  a  solution  of  tin  salt  until  im- 
pregnated, and  the  tin  hydroxide  is  fixed  by  treatment  with  cold  di- 
lute soda  solution,  or  by  merely  washing  in  water.  The  silk  is  then 
"  boiled-off  "  in  soap  liquor  to  remove  the  harsh  feel.  The  weight  is 
increased  about  25  per  cent  by  this  process.  But  stannic  chloride 
has  an  injurious  action  on  the  fibre  if  too  strong  (over  50°  Tw.)  and 
shrinks  it  very  much,  besides  destroying  certain  dyes  which  may  be 
afterwards  used. 

Acetic  acid  (p.  308)  is  largely  used  in  dyeing  and  printing,  but 
more  as  an  assistant  than  a  mordant.  It  neutralizes  many  bases 
without  affecting  the  dyeing  process,  and  it  does  not  attack  vegeta- 


518  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

ble  fibre.  Crude  pyroligneous  acid  contains  reducing  substances, 
and  because  of  this  is  used  where  oxidation  is  to  be  prevented. 

Oxalic  acid,  H2C2O4  •  2  H2O,  forms  crystals  readily  soluble  in 
water.  It  is  largely  used  in  dyeing,  mainly  as  an  addition  to  the 
dye-bath  to  retard  the  deposition  of  the  color,  and  for  a  fixing  agent 
in  mordanting  wool  with  bichromate,  aluminum  sulphate,  or  copperas. 

Tartaric  acid,  C2H2(OH)2(COOH)2,  is  often  used  as  an  addition  to 
the  mordant  bath  for  wool,  and  to  the  dye-bath  to  retard  the  dyeing, 
and  in  clearing  and  brightening  the  color  on  silk  after  dyeing ;  also 
as  a  "  resist  "  and  "  discharge  "  in  calico  printing.  The  most  im- 
portant tartrates  are  cream  of  tartar,  C4H4O4(OH)  •  (OK),  and  tartar 
emetic,  C4H4O6K  •  (SbO)  +  \  H2O. 

Citric  acid,  C3H4(OH)(COOH)3,  and  lactic  acid;  C2H4(OH)COOH 
(p.  467),  are  used  somewhat  in  place  of  tartaric  acid,  but  more  espe- 
cially as  resists,  etc.,  in  calico  printing. 

Turkey-red  oil  (p.  326),  or  soluble  oil,  is  used  as  a  mordant  on 
cotton  for  dyeing  with  basic  dyes  and  Turkey-reds,  and  for  preparing 
cloth  for  calico  printing. 

TANNINS 

Tannins,  many  of  which  are  used  in  tanning,  are  important  mor- 
dants, their  value  depending  on  the  fact  that  they  are  absorbed  by 
cotton,  linen,  and  silk,  while  they  retain  their  property  of  precipitat- 
ing insoluble  metallic  compounds  in  the  fibre,  and  also  of  uniting 
with  the  basic  dyes.  Tannins  from  different  sources  are  possibly 
not  of  the  same  composition  and  any  particular  sample  may  not  be 
homogeneous.  Some  of  the  tannins  are  glucose  esters  *  of  gallic  and 
digallic  acids ;  tannins  of  this  type  have  been  produced  synthetically, 
and  it  is  not  impossible  that  all  the  more  characteristic  tannins  are 
glucosides.  Tannic  acid,  the  most  important  of  the  tannins,  is  prob- 
ably an  ester  of  glucose  with  five  molecules  of  m-digallic  acid,  i.e.  a 
penta-gallate  of  glucose.  It  is  soluble  in  six  parts  cold  water,  and  is 
obtained  by  extracting  powdered  gall-nuts  with  water,  alcohol,  and 
ether.  On  evaporation  the  aqueous  solution  yields  the  tannin  as  a 
colorless,  or  light  yellow,  amorphous,  scaly,  or  vitreous  mass.  Tannic 
acid  is  precipitated  from  aqueous  solution  by  dilute  sulphuric,  or 
hydrochloric  acid,  by  alkalies,  chlorides,  etc.,  but  not  by  nitric  acid 
or  Glauber's  salt.  Gelatine  or  untanned  hide  removes  it  completely 
from  solution.  It  is  a  weak  acid,  but  will  decompose  alkali  carbon- 
ates. It  is  easily  oxidized,  and  reduces  many  metallic  salts,  Fehling's 

*Ber.  46  (1913),  3253. 


TEXTILE    INDUSTRIES  519 

solution,  and  permanganates.     It  forms  a  blue-black  precipitate  with 
ferric  salts,  which  is  the  basis  of  many  kinds  of  writing  ink. 

The  tannins  occur  in  numerous  plants,  being  found  in  the  roots, 
bark,  wood,  leaves,  flowers,  fruit,  seed-pods,  or  in  excrescences  on  the 
plant.  The  chief  commercial  sources  are  gall-nuts,  sumach,  oak  and 
hemlock  bark,  mimosa  bark,  chestnut  wood,  cutch  (catechu),  gambier, 
myrabolans,  valonia,  divi-divi,  kino,  quebracho,  and  canaigre. 

Galls,  or  nut-galls,  are  excrescences  on  various  kinds  of  oak  trees, 
produced  by  the  sting  of  the  female  gall  wasp,  Cynips  galloe  tinctorice, 
Oliv.,  and  in  which  the  eggs  are  deposited.  Young  nut-galls,  from 
which  the  insect  has  not  yet  escaped,  are  greenish  or  bluish  in  color, 
and  are  rich  in  tannin ;  afterwards  they  become  yellow,  and  the 
percentage  of  tannin  is  much  decreased.  The  best  qualities  come 
from  Persia,  but  the  Levant  galls,  from  Smyrna  and  Tripoli,  contain 
from  55  to  60  per  cent  tannic  acid  and  some  gallic  acid.  Poorer 
grades  come  from  Italy,  France,  Germany,  and  Austria. 

Japanese  and  Chinese  galls  are  "caused  by  the  sting  of  an  insect 
(plant  louse)  on  the  leaves  of  plants  (Rhus  semialata,  Murr.)  of  the 
sumach  family.  These  galls  are  irregular  in  shape,  and  are  light 
and  hollow,  but  contain  70  per  cent  tannin,  or  even  more. 

Sumach  of  commerce  consists,  of  the  leaves  and  young  twigs  from 
various  plants  of  the  Rhus  family,  especially  Rhus  Coriaria,  L. ; 
poorer  grades  are  derived  from  R.  Cotinus,  L.  These  shrubs  are 
found  in  many  countries,  but  Italy,  Spain,  Greece,  and  Virginia  fur- 
nish the  better  grades.  Sumach  is  largely  used  in  mordanting,  since 
it  contains  very  little  coloring  matter  to  stain  the  goods.  Good  sam- 
ples contain  from  15  to  20  per  cent  of  tannin,  and  are  sold  as  a  fine 
powder,  or  as  leaves,  mixed  with  twigs  and  stems.  'Much  is  now 
sold  as  "  extract,"  a  thick  brown  liquid  obtained  by  evaporating  the 
aqueous  solution,  usually  in  vacuum. 

Catechu,  or  cutch  (terra  japonica),  is  obtained  from  the  wood  and 
pods  of  Acacia  Catechu,  Willd.,  and  from  the  betel  nut,  the  fruit 
of  the  Areca  Catechu,  L.,  a  species  of  palm-tree.  Both  plants  are 
natives  of  India.  Cutch  appears  in  commerce  as  dark  brown,  irregu- 
lar lumps,  which  dissolve  in  water,  forming  a  dark  brown  solution. 
It  contains  a  tannin  called  catechu-tannic  acid,  and  another  body, 
catechin.  It  is  extensively  used  as  a  brown  dye  on  cotton,  for  calico 
printing,  and  also  in  the  weighting  of  black  silks.  It  is  a  good  mor- 
dant for  certain  basic  coal-tar  dyes,  when  employed  in  dyeing  com- 
pound shades.  On  cotton,  copper  salts  should  always  be  used  in 
conjunction  with  cutch. 


520  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

Gambier  is  extracted  from  the  leaves  of  an  Indian  shrub,  Uncaria 
dasyoneura,  Korth.  It  has  a  yellow  color,  and  is  used  somewhat  as 
a  pigment  and  as  a  yellow  dye.  It  is  slightly  soluble  in  cold  water, 
and  very  readily  so  in  hot  water.  In  commerce  it  appears  as  small 
cubical  blocks,  containing  about  40  per  cent  tannin,  chiefly  as  cate- 
chu-tannic  acid.  Gambier  is  used  in  silk  and  cotton  dyeing,  much 
in  the  same  way  as  catechu.  It  is  extensively  used  in  tanning  Mo- 
rocco leather. 

Myrabolans  are  the  dried  fruit  of  certain  Indian  and  Chinese 
trees,  Myrobolanus  Chebula,  Gsert.  They  appear  in  commerce  as 
dried  and  shrivelled  nuts  about  an  inch  long,  containing  about  30 
per  cent  tannin  (ellagitannic  acid),  and  also  a  brownish  coloring 
matter.  They  are  used  in  place  of  tannic  acid,  for  some  purposes  in 
mordanting  cloth,  and  also  in  weighting  black  silks. 

Valonia  is  the  acorn  cups  of  an  oak,  Quercus  JEgilops,  L.,  native 
of  Greece,  Asia  Minor,  and  France.  The  cups  are  very  large,  and  cov- 
ered with  coarse  hair,  or  "  beard,"  which  is  especially  rich  in  tannin. 
They  are  drab  in  color,  and  contain  a  yellow  coloring  matter.  Good 
valonia  contains  about  30  per  cent  of  true  tannic  acid. 

Divi-divi  is  the  fruit  of  a  West  Indian  tree,  Ccesalpinia  coriaria, 
Willd.  It  forms  very  thin  pods  about  three  inches  long,  and  often 
folded  and  twisted,  and  containing  about  30  per  cent  of  ellagitannic 
acid,  with  some  gallic  acid.  The  color  of  the  pods  varies  from  light 
brown  to  black,  and  considerable  coloring  matter  is  present,  which 
stains  the  goods.  It  is  used  for  mordanting  blacks  on  cotton  and  silk. 

Chestnut,  Castanea  saliva,  Mill.,  furnishes  a  tannin  extract,  the 
composition  of  whose  tannin  is  unknown.  The  extract  is  a  black 
solid,  or  a  brown  syrup,  forming  turbid  solutions  with  water.  It  is 
extensively  used  in  weighting  black  silk. 

Kino  is  the  dried  sap  of  certain  trees,  Pterocarpus  Marsupium, 
Roxb.,  Butea  frondosa,  Roxb.,  and  Eucalyptus  rostrata,  Schlecht.  It 
forms  small  garnet-red  angular  grains,  slightly  soluble  in  water,  and 
contains  a  large  quantity  of  kinotannic  acid,  a  substance  of  unknown 
composition.  The  chief  supplies  come  from  India,  Africa,  and 
Australia.  It  is  chiefly  used  in  medicine,  and  resembles  catechu. 

Oak  and  hemlock  bark  are  rich  in  tannins,  containing  about  15 
per  cent,  but  they  are  contaminated  with  certain  anhydride  substances 
which  are  slightly  soluble  in  water,  and  color  the  goods  a  deep  brown 
or  red,  and  hence  are  unsuitable  for  mordants.  These  anhydrides 
are  called  phlobaphenes,  and  are  much  like  the  tannins  in  their  action, 
combining  with  fibre'  and  precipitating  gelatine,  ferric  salts,  etc. 


TEXTILE    INDUSTRIES  521 

These  barks  are  extensively  used  for  making  leather,  especially 
the  heavy  and  strong  kinds. 

Mimosa  bark  (Wattle)  is  obtained  from  several  species  of  Acacia 
in  Australia,  Natal,  and  South  America.  It  contains  from  24  to  40 
per  cent  tannins. 

Quebracho  is  an  extract  made  from  hardwood  trees,  Aspidosperma 
Quebracho,  Schlecht,  and  Quebrachia  Lorentzii,  Griseb.,  natives  of 
South  America.  It  contains  about  25  per  cent  of  tannins,  contami- 
nated with  red  coloring  matter. 

Canaigre  is  obtained  from  the  roots  of  a  species  of  dock,  Rumex 
hymenosepalus,  Torr.,  a  native  of  Arizona  and  New  Mexico.  It  is 
now  extensively  cultivated  in  the  southwestern  part  of  the  United 
States.  It  contains  about  30  per  cent  of  tannin,  together  with  a 
bright  yellow  coloring  matter,  much  resembling  gambier.  It  is 
always  sold  as  extract. 

Extracts  are  now  prepared  from  nearly  all  of  the  above  tannin 
substances,  by  treating  them  with  water  and  evaporating  the  tannin 
solution  to  a  thick  syrup,  or  even  to  dryness,  generally  by  the  aid  of 
vacuum.  These  extracts  are  much  more  economical  to  ship,  and 
more  convenient  to  use,  but  are  frequently  adulterated  with  glucose 
or  other  matter. 

COLORING  MATTERS 

According  to  their  origin  coloring  matters  may  be  classified 
broadly  into  three  groups :  (1)  Natural  Organic  Dyes  tuffs  (Vegetable 
and  Animal) ;  (2)  Artificial  Organic  Dyestuffs ;  (3)  Mineral  Dye- 
stuffs.  For  practical  purposes,  however,  a  classification  based  upon 
the  method  of  application  to  the  fibres  (p.  531)  is  more  convenient. 

NATURAL  DYESTUFFS 

Natural  dyestuffs  have  been  employed  for  textile  coloring  since 
prehistoric  times.  They  are  soluble  in  water  and  have  more  or  less 
tendency  to  combine  directly  with  the  fibres.  Many  of  them  are 
not  in  themselves  dyes,  but  form  color  lakes  by  combination  with 
mordants.  In  recent  years  they  have  been  very  generally  replaced 
by  the  more  brilliant  and  readily  applied  artificial  colors. 

Indigo  is  one  of  the  oldest  known  dyes,  and  probably  originated 
in  India.  It  exists  in  the  indigo  plant,  Indigofera  tinctoria,  L.,  and 
in  woad,  I  satis  tinctoria,  L.,  in  the  form  of  a  glucoside,  indican, 
C26H3iNOi7,  which  is  decomposed  by  acids  to  form  the  coloring  prin- 
ciple indigotine,  Ci6HioN2O2,  and  a  sugar.  To  isolate  the  coloring 


522  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

matter,  the  stems  and  leaves  of  the  plant  are  put  into  a  cemented 
cistern  and  covered  with  water.  A  fermentation  soon  begins,  caus- 
ing a  rise  in  the  temperature,  while  the  indican  is  decomposed  and 
the  sugary  matter  destroyed;  at  the  same  time,  the  indigo  is  reduced 
to  indigo  white,  deH^^C^.  This  dissolves  to  form  a  greenish- 
yellow  liquid,  which  is  drawn  off  into  vats  and  violently  stirred  and 
splashed  by  the  workmen  for  several  hours,  in  order  to  thoroughly 
aerate  and  oxidize  the  indigo  white.  The  blue  pigment  precipitates, 
and  after  settling,  the  liquor  is  drained  off.  The  magma  is  repeatedly 
washed  and  finally  boiled,  to  prevent  any  further  fermentation, 
and  is  filtered,  drained  in  cloth-lined  frames,  and  finally  pressed 
into  cakes;  these  are  carefully  dried,  away  from  the  sunlight.  The 
yield  is  about  0.2  to  0.3  per  cent  of  the  weight  of  the  plant. 

The  indigo  of  commerce  forms  dark  blue  cubical  cakes  having 
a  matt,  earthy  appearance  on  the  fractured  surface.  Its  content 
of  pure  indigo  varies  from  20  to  90  per  cent  and  averages  about 
45  per  cent.  It  contains  indigo  red  and  indigo  brown,  which  affect 
the  shade  of  the  blue;  also  moisture  and  mineral  and  glutinous 
substances.  Indigo  is  tasteless,  odorless,  insoluble  in  water,  alcohol, 
ether,  dilute  acids  or  alkalies.  By  careful  heating  it  sublimes.  If 
very  finely  powdered,  concentrated  and  fuming  sulphuric  acid  dissolve 
it  to  form  mono-  and  disulphonic  acids,  the  latter  being  soluble  in 
water.  The  sodium  salts  of  these  indigo  sulphonic  acids  constitute 
the  indigo  extract,  soluble  indigo,  or  indigo  carmine  of  commerce. 
These  are  obtained  by  neutralizing  the  sulphuric  acid  solution  of 
indigo  with  sodium  carbonate,  and  precipitating  the  indigo  carmine 
by  adding  common  salt.  True  indigo  carmine  is  the  sodium  salt  of 
the  disulphonic  acid,  and  is  dyed  on  animal  fibres  as  an  acid  dye, 
p.  535  ;  when  sold  as  a  dry  powder  it  is  called  "  indigotine." 

The  vegetable  indigo  industry  is  now  greatly  diminished  through 
competition  by  the  artificial  product. 

Artificial  indigo  has  almost  entirely  replaced  natural  indigo 
since  about  1910,  its  successful  production  on  a  commercial  scale 
being  the  result  of  long  series  of  investigations  and  experiments. 
But  none  of  the  various  syntheses  proposed  were  feasible,  until  the 
discovery  that  naphthalene  could  be  used  as  raw  material. 

Naphthalene  is  oxidized  to  phthalic  anhydride  by  fuming  sulphuric 
acid  in  the  presence  of  mercury  bisulphate  to  moderate  the  reaction ; 
the  sulphur  dioxide  liberated  is  recovered  for  use  in  the  "  contact 
sulphuric  acid  process."  The  phthalic  anhydride  is  converted  into 
phthalimide,  which  by  oxidation  with  chlorine  yields  anthranilic 


TEXTILE    INDUSTRIES  523 

acid.  This  by  treatment  with  monochloracetic  acid  yields  phenyl- 
glycine-o-carboxylic  acid,  which  by  fusion  with  caustic  potash* 
forms  indoxylic  acid  and  indoxyl ;  these  are  converted  into  indigo  by 
oxidation  with  air. 

For  methods  of  indigo  dyeing,  see  p.  541. 

Logwood  is  the  heart  wood  of  a  tropical  tree,  Hoematoxylon 
Campechianum,  L.,  native  in  Central  America.  It  is  brought  into 
commerce  in  the  form  of  logs,  chips,  and  extract.  The  chromogen 
(p.  527)  in  the  wood  is  hcematoxylin,  CieHuOe,  which  forms  nearly 
colorless  crystals  when  pure;  it  exists  in  the  wood  as  a  glucoside 
and  partly  in  the  free  state.  It  is  readily  oxidized,  especially  in  the 
presence  of  an  alkali,  to  form  hsematein,  CieH^Oe,  which  is  the  real 
dyestuff.  This  forms  colored  lakes  with  metallic  bases,  yielding 
violets,  blues,  and  blacks  with  the  various  mordants. 

The  logs  are  chipped  or  rasped  to  form  a  coarse  powder,  which 
does  not  contain  much  hsematein  when  fresh,  the  dyestuff  being 
formed  by  "  curing  "  or  oxidizing.  The  rasped  wood  is  fermented 
by  moistening  with  water  and  exposing  in  heaps  to  the  air.  To 
control  the  temperature  and  give  better  exposure,  the  heap  is  shov- 
elled over  and  sprinkled  with  water  at  frequent  intervals,  until  the 
chips  assume  a  deep,  reddish-brown  color,  or  even  develop  a  bronze 
shade.  Alkalies,  potassium  nitrate,  chalk,  or  ammonium  chlorate 
are  sometimes  added  to  hasten  the  process.  The  cured  chips  yield 
a  decoction  which  is  rapidly  taken  up  by  the  fibre  in  dyeing  opera- 
tions. The  amount  of  water  in  cured  chips  is  nearly  double  that 
contained  in  the  fresh  wood. 

Most  "  extract  "  of  logwood  is  now  made  from  chips  which  are 
not  cured.  They  are  put  into  an  extractor,  an  iron  vessel  provided 
with  a  false  bottom  and  a  perforated  steam  coil.  The  extractors 
are  often  set  in  batteries,  so  arranged  that  the  liquor  from  one  flows 
into  the  next  more  recently  filled  vessel,  finally  leaving  that  con- 
taining the  freshest  wood.  Pressure  extraction  is  often  used,  but  an 
increase  of  over  15  pounds  is  liable  to  cause  decrease  in  the  coloring 
power  of  the  product.  After  settling  to  separate  wood  fibre  and 
resin,  the  liquid  from  the  extractors  is  evaporated  in  vacuum  pans, 
the  Yaryan  being  often  used  for  the  dilute  liquors.  When  it  becomes 
thick,  the  evaporation  is  continued  in  a  common  vacuum  pan  (strike 
pan)  until  a  density  of  about  50°  Tw.  is  reached  for  liquid  extract ; 
or  it  may  be  continued  until  a  solid  extract  is  obtained  on  cooling. 

*  Better  yields  are  obtained  if  sodamide  is  used  instead  of  caustic  potash  for 
the  fusion,  but  its  price  is  relatively  high, 


524  OUTLINES   OF    INDUSTRIAL   CHEMISTRY 

Throughout  the  process,  precautions  are  taken  to  prevent  access  of 
air  and  consequent  oxidation  of  the  product.  The  use  of  chemicals 
to  develop  the  color  in  the  extract  itself  is  of  doubtful  value,  as  this 
development  should  only  take  place  in  the  dye-bath.  The  yield 
of  solid  extract  is  about  20  per  cent  with  pressure,  and  without  press- 
ure about  16  per  cent. 

Logwood  extract  is  frequently  adulterated  with  glucose,  molasses, 
and  chestnut,  hemlock,  and  quercitron  extracts.  Logwood  is  chiefly 
used  with  a  chrome  or  iron  mordant  for  blacks  on  wool  and  cotton. 

Red  woods  of  commerce  are  Brazil  wood,  Ccesaljrinia  Brasiliensis, 
L.,  and  Pernambuco  wood  (C.  Crista,  L.),  from  Brazil,  West  Indies, 
and  Bahama;  sappan  wood,  C.  Sappan,  L.,  from  China,  Japan,  and 
Siam ;  Lima  wood,  C.  bijuga,  Sw.,  from  Central  America ;  and  peach 
wood,  C.  echinata,  Lam.  These  contain  the  chromogen  brazilin, 
CieHuOs,  which  is  chemically  related  to  haematoxylin.  Brazilin  is 
colorless,  but  dissolves  in  alkalies,  forming  a  red  solution  which 
oxidizes  on  exposure  to  the  air,  forming  brazilein,  CieH^Os;  this 
combines  with  alumina  to  form  red  lake  similar  to  alizarin  red,  but 
more  fugitive. 

Another  class  of  red  woods  contains  santalin  (CisHuOs).  These 
resemble  Brazil  woods  in  color,  but  are  heavier  and  of  harder  tex- 
ture. The  more  common  ones  are  sandal  wood,  Pterocarpus  santa- 
linus,  L.,  from  Madagascar  and  the  East  Indies ;  barwood,  Baphia 
nitida,  Lodd.,  and  camwood. 

Madder  is  the  pulverized  root  of  Rubia  tindorum,  L.,  a  plant 
formerly  largely  cultivated  in  Europe  and  Asia  Minor.  It  contains 
glucosides  which  are  decomposed  by  fermentation,  forming  alizarin, 
Ci4H6O2(OH)2,  and  purpurin,  Ci4H5O2(OH)3,  which  are  identical  with 
di-  and  trioxyanthrachinon.  Madder  extract  is  prepared  by  fer- 
mentation and  evaporation  of  the  filtered  solution,  yielding  "  gar- 
ancine  "  and  "  madder  flowers." 

Madder  has  been  used  for  ages  in  dyeing  Turkey-red  on  cotton, 
affording  one  of  the  brightest  and  fastest  colors.  But  in  1868, 
Grsebe  and  Liebermann  made  artificial  alizarin  from  anthracene 
derived  from  coal-tar.  In  consequence  of  this  discovery,  the  madder 
industry  has  nearly  disappeared. 

Alizarin  is  made  from  anthracene  by  oxidizing  the  latter  with 
chromic  acid,  to  form  anthraquinone.  This  is  treated  with  fuming 
sulphuric  acid,  which  converts  it  into  a  monosulphonic  acid,  soluble 
in  water.  By  neutralizing  with  caustic  soda,  the  difficultly  soluble 
sodium  salt  is  precipitated  from  the  solution.  The  sodium  salt  is 


TEXTILE    INDUSTRIES  525 

mixed  with  caustic  soda  and  an  oxidizing  agent  (KC1O3)  and  heated 
for  two  days  in  an  autoclave  at  180°  C.,  whereby  the  sulphonic  group 
is  replaced  by  hydroxyl,  and  another  hydroxyl  group  is  introduced 
in  the  ortho  position  to  the  first.  By  dissolving  the  fused  mass  in 
water  and  adding  sulphuric  acid,  the  alizarin  is  precipitated  as  a 
nearly  insoluble  yellow  mass,  which  is  brought  into  commerce  as  a  wet 
paste  containing  about  20  per  cent  of  coloring  matter.  Other  methods  * 
of  preparation  without  sulphonation  are  also  in  use. 

Archil  or  orseille  (cudbear)  is  an  important  dyestuff  derived 
from  certain  lichens,  Roccella  tinctoria,  D.  C.,  R.fuciformis  (L.)  D.  C., 
indigenous  in  Madagascar,  Zanzibar,  Azores,  Ceylon,  and  France,  and 
Lecanora  tartar ea,  Achar.,  from  Sweden.  They  contain  mixtures  of 
phenols  and  phenol  acids,  which,  when  treated  with  ammonia  and 
exposed  to  the  air,  yield  orcein,  a  violet  powder  sold  as  "  cudbear." 
It  is  either  a  paste  or  powder  prepared  by  evaporating  the  aqueous 
extract  to  dryness  in  vacuum.  The  powder  dissolves  in  alkalies 
and  forms  colored  lakes  with  heavy  metals  and  lime.  It  was  for- 
merly much  used  in  wool  dyeing,  yielding  violet  and  red  shades. 

Litmus  is  obtained  by  treating  the  above-mentioned  lichens  with 
ammonia  and  potash,  and  fermenting  the  mass.  The  dyestuff  forms 
a  red  color-acid,  whose  alkali  salts  are  blue.  The  commercial  article 
consists  of  calcium  carbonate,  or  sulphate,  which  is  mixed  with  the 
coloring  matter  and  formed  into  small  cubes.  It  is  not  used  as  a 
dye,  but  is  interesting  because  of  its  use  as  an  indicator. 

Cochineal  consists  of  the  dried  bodies  of  the  female  insects,  Coccus 
cacti.  These  insects  live  on  certain  cactus  plants  in  Mexico,  Cen- 
tral America,  Algeria,  and  the  East  Indies;  they  are  collected, 
and  killed  by  placing  them  in  ovens  or  in  hot  water,  or  by  steaming 
them.  When  killed  by  dry  heat,  the  cochineal  is  coated  with  a 
silvery  gray  powder,  consisting  of  a  wax,  coccerin;  but  if  boiled  or 
steamed,  the  cochineal  is  "  black,"  and  of  less  tinctorial  power.  The 
silver  gray  is  often  imitated  by  dusting  the  black  cochineal  with 
powdered  stearic  acid  or  talc.  The  coloring  principle  is  carminic 
acid,  CivHigOio,  a  glucoside,  soluble  with  a  deep  red  color  in  water, 
and  forming  scarlet  lakes  with  alumina  and  tin  salts.  Cochineal 
contains  about  10  per  cent  carminic  acid.  The  dye  is  chiefly  used 
on  wool.  Cochineal  yields  the  pigment  carmine  (p.  245). 

Lac  dye  is  also  obtained  from  an  insect,  Coccus  lacca,  which  exudes 
the  lac  resin  (p.  396).  The  collection  and  preparation  of  the  resin  in- 
volve the  preparation  of  the  dye.  The  latter  is  very  similar  to  carminic 
acid,  and  is  prepared  by  extracting  the  gum  with  sodium  carbonate, 


526  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

Kermes  is  similar  to  cochineal,  and  consists  of  dried  insects, 
Coccus  ilicis,  from  northern  Africa  and  Spain.  It  is  seldom  used  in 
dyeing  at  the  present  time. 

Fustic  is  the  heart  wood  of  Chlorophora  tinctoria,  Gaud.,  or 
Madura  tinctoria,  native  in  West  Indies  and  tropical  South  America. 
It  yields  a  coloring  principle,  morin,  C^HioOy  •  2  H2O,  which  forms 
lemon  yellow  lakes  with  alumina.  It  is  sold  as  chips,  and  as  an 
extract,  and  is  chiefly  used  for  wool  dyeing,  especially  for  modifying 
the  shade  of  logwood  and  other  dyes. 

Young  fustic  is  the  heart  wood  of  a  sumach,  Rhus  Cotinus,  L., 
native  in  Spain,  Italy,  Hungary,  and  the  Levant.  It  yields  an 
orange-colored  lake  with  alumina  and  tin.  The  color  principle  is 
fisetin,  CisHioOe. 

Quercitron  is  the  powdered  bark  of  the  North  American  tree, 
Quercus  coccinea,  var.  tinctoria,  Gray.  It  contains  a  dyestuff,  quer- 
citrin,  C2iH2oOn  •  2  H2O,  which  is  converted  by  dilute  acid  into  quer- 
cetin,  CisHioOy,  and  isodulcit,  CeH^Os.  Quercetin  dissolves  in  alkali 
with  a  yellow  color,  and  forms  yellow  lakes  with  alumina  and  tin. 
By  extracting  the  bark  with  alkali,  and  neutralizing  the  extract  with 
sulphuric  acid,  a  mixture  of  quercitrin,  quercitin,  and  isodulcit  is 
obtained,  which  appears  in  commerce  as  "  flavine."  Both  the  bark 
and  the  extract  are  used  in  wool  dyeing  and  calico  printing. 

Persian  berries  are  the  dried  fruit  (berries)  of  certain  buckthorn 
(Rhamnus)  species,  growing  throughout  southern  Europe.  The  col- 
oring principle  is  a  glucqside,  which  is  decomposed  by  acids  into 
isodulcit  and  rhamnetin,  CieH^O?,  the  latter  being  the  dyestuff.  It 
forms  yellow  and  orange  shades  with  alumina  and  tin,  and  is  mainly 
used  in  calico  printing. 

Curcuma,  or  turmeric,  is  the  dried  root  of  various  species  of 
Curcuma  of  Central  Asia.  The  dyestuff  is  curcumin,  C^Hi^,  or 
C2iH2oO6,  which  yields  a  tolerably  fast  yellow  on  cotton.  It  is  also 
used  to  color  oils  and  wax. 

Annatto  (arnotto)  is  obtained  from  the  fruit  of  the  West  Indian 
and  South  American  trees,  Bixa  Orellana,  L.  It  contains  the  orange 
dye,  bixin,  C28H34O5,  and  comes  in  commerce  as  a  thick  paste,  or  dry 
cakes.  It  is  mainly  used  for  coloring  butter  and  cheese. 

Cutch  is  described  on  p.  519. 

ARTIFICIAL  DYESTUFFS 

The  artificial  organic  dyestuff  industry  originated  in  England 
with  the  discovery  of  the  lilac  color,  mauve,  by  Perkin,  in  1856, 


TEXTILE    INDUSTRIES  527 

This  was  obtained  by  direct  oxidation  of  aniline  containing  toluidine. 
In  1859  Verguin  made  magenta,  or  fucHsine,  and  each  following 
year  other  colors  were  discovered,  until  at  the  present  time  there  are 
several  thousand  dyes  on  the  market,  and  a  stupendous  industry  has 
arisen  in  their  manufacture.  Because  the  first  artificial  dyes  were 
prepared  from  aniline,  the  colors  were  known  as  "  aniline  dyes,"  a 
name  still  applied  to  them,  but  they  are  now  more  properly  called 
"  coal-tar  dyestuffs."  They  are  made  from  various  aromatic  sub- 
stances largely  derived  from  coal-tar,  especially  the  benzene  hydro- 
carbons, phenols,  and  pyridine  bases. 

The  relation  of  the  color  to  the  constitution  in  the  coal-tar  dyes 
has  been  explained  by  Witt.*  He  shows  that  the  introduction  of 
certain  groups  (called  chromophores)  into  colorless  aromatic  hydro- 
carbons produces  colored  substances  called  chromogens.  The 
chromogens  possess  very  slight  coloring  power  in  themselves,  but  are 
converted  into  dyestuffs  by  the  addition  of  certain  salt-forming 
(auxochromous)  groups,  such  as  hydroxyl  (OH),  or  the  amino  group 
(NH2).  Thus  benzene  is  colorless,  but  the  introduction  of  chromophor 
groups,  such  as  the  nitro  group  (NO2),  or  the  azo  group  (—  N  =  N  — ), 
forms  the  colored  chromogens,  mono-,  di-,  and  tri-nitrobenzene,  or 
azobenzene.  The  chromogens  may  take  on  the  auxochromous 
groups  (OH)  or  (NH2),  and  form  dyestuffs  such  as  picric  acid, 
C6H2(NO2)3(OH),  or  amino-azobenzene,  C6H5N  =  NC6H4  •  NH2.  If 
the  auxochromous  groups  are  converted  into  salts,  the  color  is  much 
intensified ;  thus  sodium  picrate  is  a  deeper  yellow  than  picric  acid. 
But  the  sulpho-group,  SO3H,  and  the  carboxyl  group,  CO2H,  are  not 
auxochromous,  notwithstanding  that  they  form  salts,  and  they 
impart  little  tinctorial  power  to  the  chromogens.  From  this  Witt 
drew  the  following  conclusions :  — 

(1)  The  simultaneous  occurrence  of  a  chromophor  and  an  auxo- 
chromous group  is  essential  to  the  development  of  tinctorial  prop- 
erties in  an  aromatic  substance. 

(2)  The  chromophor  exerts  a  greater  color-generating  influence 
in  the  saltlike  derivatives  of  the  dyestuff  than  in  the  free  compounds. 

(3)  In  the  case  of  dyes  of  similar  constitution,  the  one  having  the 
more  stable  salts  is  the  better. 

A  classification  of  the  synthetic  dyestuffs  according  to  their 
constitution,  with  reference  to  Witt's  theory,  may  be  made,  but  for 

*  Ber.  d.  deutsch.  Chem.  Gesel.  9  (1876),  522. 


528  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

practical  uses  a  grouping  according  to  the  methods  of  application  to 
the  textile  fibres  is  more  useful  (see  p.  531). 

Classified  according  to  structure  the  following  groups  *  are  dis- 
tinguished :  —  ^  p Q 

I.  Nitroso-  or  Quinoneoxime  derivatives ;  chromophor,     |        | 

>C— N-OH 

II.  Nitro  derivatives ;  chromophor,  — NO2 
AyIII.  Azo  dyestuffs  ;  chromophor,  — N  =  N— 
N/IV.  Triphenylmethane  dyestuffs ;  chromophor,  =  <H>  = 

V.  Pyronine  dyes ;  chromophor,  '      ^ 

\C/ 

VI.  Acridine  dyestuffs ;  chromophor,       |    /  CO 

VII.  Oxyketone  dyestuffs;    chromophor, 

VIII.  Oxazine  dyes  ;  chromophor,  /   ^  CO 

\N-^ 

IX.  Thiazine  dyes ;  chromophor, 


X.  Azine  dyes ;  chromophor,  or 

\]sj/ 

XL  Miscellaneous  dyestuffs. 

The  limits  of  this  book  will  not  permit  a  full  consideration  of  the 
individual  dyestuffs,  and  for  them  recourse  must  be  had  to  the  hand- 
books mentioned  in  the  list  of  references. 

Dyestuffs  are  often  called  substantive  and  adjective ;  the  former 
will  color  fibres  directly,  the  latter  will  only  color  with  any  perma- 
nence when  used  in  conjunction  with  a  mordant.  Nietzki  desig- 
nates f  the  two  classes  as  direct  dyes  and  mordant  dyes.  Hummel 
divides  {  coloring  matters  into  monogenetic,  or  those  which  produce 
only  one  color  under  any  condition  ;  poly  genetic,  those  which  produce 
several  colors,  according  to  the  mordant  used. 

DYEING 

Dyeing  is  the  process  of  precipitating  coloring  matter  upon,  or 
within,  the  substance  of  a  body  which  is  to  be  colored.  Dyestuffs 
are  distinguished  from  pigments  by  the  fact  that  they  are  soluble  in 

*  After  Gardner  in  the  Dictionary  of  Applied  Chemistry,  2d  ed.,  Vol.  II,  282. 

t  Farber-Zeit.,  1889-90. 

J  Dyeing  of  Textile  Fabrics,  p.  147. 


TEXTILE    INDUSTRIES  529 

water,  or  in  the  liquid  of  the  dye-bath,  from  which  solution  they  are 
abstracted  by  the  material  to  be  dyed.  In  the  majority  of  cases 
dyes  are  applied  to  textile  fibres  or  fabrics,  but  occasionally  natural 
products,  such  as  straw,  feathers,  horn,  leather,  ivory,  bone,  or  wood 
may  be  dyed.  The  substance  is  immersed  in  a  hot  or  cold  aqueous 
solution  of  the  dyestuff,  except  in  a  few  rare  cases  where  other  sol- 
vents than  water  may  be  used,  or  the  solution  applied  as  a  spray. 
The  solution  may  be  acid,  alkaline,  or  neutral,  according  to  the  nature 
of  the  material  and  of  the  dyestuff ;  thus  alkaline  or  neutral  baths  are 
generally  used  for  cotton  and  vegetable  fibres,  neutral  or  acid  baths 
for  wool,  and  acid  or  alkaline  baths  for  silk. 

Several  theories  concerning  the  nature  of  the  dyeing  process 
have  been  proposed.  The  mechanical  theory  assumes  the  coloring 
to  be  due  to  mechanical  absorption  of  the  dye  within  the  capillary 
tubes  and  pores  of  the  fibres.  The  inability  of  many  dyes  to  color 
all  fibres  equally  well  is  ascribed  to  the  different  size  of  the  pores 
of  the  fibres,  relative  to  the  size  of  the  dye  molecules.  Also  the 
size  of  the  pores  may  be  affected  by  heat,  or  by  the  action  of  certain 
chemicals,  as  astringents. 

The  chemical  theory*  supposes  a  chemical  combination  to  take 
place  between  the  coloring  matter  and  some,  or  all,  of  the  constituents 
of  the  fibre,  f  It  has  been  shown  that  silk  and  wool,  when  brought 
into  reaction  with  many  dyes,  will  set  free  the  acid  united  with  the 
color  base ;  also  that  the  colorless  rosaniline  base  in  the  dye-bath  will 
color  wool  by  the  formation  of  a  salt  with  the  constituents  of  the 
fibre.  The  action  of  silk  and  wool  towards  acids  and  bases  is  in 
general  similar  to  that  of  amino-acids,  of  which  these  fibres  are  con- 
densation products.  The  relative  fastness  of  a  color  on  different 
fibres  is  also  in  accord  with  the  chemical  theory. 

The  solid  solution  theory,  advanced  by  O.  N.  Witt  in  1889,  supposes 
that  dyeing  consists  in  the  formation  of  a  solid  solution  of  the  dye, 
or  of  the  mordant  in  the  case  of  mordant  colors,  in  the  fibre,  anal- 
ogous to  the  solution  of  metallic  oxides  in  colored  glass.  The  color- 
ing substance  is  withdrawn  from  its  liquid  solution  in  the  dye-bath 
and  passes  into  the  fibre,  the  fibre  substance  acting  as  the  solid  sol- 
vent ;  this  action  is  similar  to  the  extraction  of  a  substance  from  its 
aqueous  solution,  by  ether  or  other  solvent  in  which  the  body  is  more 
readily  soluble  than  it  is  in  water. 

*  See  Knecht,  Jour.  Soc.  Chem.  Ind.,  1889,  457. 

t  This  applies  to  animal  fibres  but  is  difficult  to  reconcile  with  the  chemical  in- 
ertness of  cellulose. 


530  OUTLINES   OF    INDUSTRIAL   CHEMISTRY 

Recent  investigations  *  indicate  that  dyeing  is  due  to  adsorption 
of  the  colloidal  coloring  substance  on  the  surface  of  the  fibre,  and 
that  the  amount  of  color  deposited  from  solution,  on  any  kind  of 
fibre,  depends  on  the  same  laws  that  control  the  adsorption  of  gases, 
or  of  dissolved  substances,  upon  the  surface  of  adsorbing  media,  such 
as  bone-black,  etc.  It  has  been  found  experimentally,  that  in  adsorp- 
tion processes,  the  amount  of  substance  condensed  on  the  surface  of 
the  adsorbing  agent  is  a  power  function  of  the  concentration  of  the 
adsorbed  material,  whether  this  exists  as  a  gas,  or  in  solution,  and 
furthermore,  it  has  been  shown  that  the  removal  of  many  dyestuffs 
from  solution  by  such  diversified  substances  as  cotton,  silk  and  wool 
fibres,  bone-char,  precipitated  silica,  metallic  hydroxides,  etc.,  follows 
this  law ;  and  also  that  the  constants  of  the  adsorption  equation  are 
of  the  same  order  of  magnitude  for  the  different  adsorbing  agents. 
Thus  according  to  Freundlich,  and  others,  dyeing  phenomena  obey 

x  - 

the  formula  —  =  K  •  Cn,  where  x  denotes  the  weight  of  color  taken 

from  solution ;   m  is  the  weight  of  fibre  dyed ;   C  is  the  final  concen- 
tration of  color  in  the  dye-bath ;  and  K  and  --  are  constants. 

This  last  hypothesis  seems  to  throw  more  light  on  the  nature 
of  the  dyeing  process  than  any  of  the  others,  and  while  in  some  cases 
chemical  action  with  the  fibre  and  the  mordant  undoubtedly  plays  a 
part,  in  the  following  the  facts  given  will  in  general  be  interpreted  in 
terms  of  the  adsorption  theory. 

The  methods  of  dyeing  and  composition  of  the  dye-bath  vary 
with  the  nature  of  the  fibre  and  of  the  dye.  Silk  and  wool  are  often 
dyed  directly,  although  mordants  are  frequently  used ;  cotton  and 
linen  have  much  less  affinity  for  coloring  matters ;  dyes  of  the  ben- 
zidine  class  and  the  sulphur  colors  are  used  for  these  fibres  directly, 
but  basic  and  mordant  colors  require  the  fibre  to  be  mordanted. 

The  character  of  the  water  is  very  important  in  dyeing.  Iron  is 
the  most  injurious  impurity,  since  it  dulls  (saddens)  the  shade  of 
most  colors.  Hard  water  containing  lime  or  magnesium  salts  should 
generally  be  purified  before  use,  but  in  a  few  cases,  as  in  dyeing  Turkey- 
reds,  and  with  logwood,  a  little  lime  is  beneficial.  Suspended  dirt 
must  be  removed. 

The  tanks  used   for  dyeing  are  usually  made  of   iron;    but   for 

*  Miiller  and  Slassarski.  Krafft,  J.  Soc.  Dyers  and  Col.,  1899,  211.  Biltz,  ibid., 
1904,  145. 


TEXTILE    INDUSTRIES  531 

certain  delicate  colors,  especially  on  silk,  they  are  made  of  wood,  so 
put  together  that  no  metal  comes  in  contact  with  the  dye-liquor. 
The  pipes  and  coils  used  for  heating  are  generally  copper. 

Loose  cotton  and  wool  are  dyed  by  submerging  in  vats  filled  with 
the  dye-liquor.  Or  the  mass  of  fibre  may  be  compressed  into  a 
closed  vat  having  a  false  bottom,  the  liquor  being  circulated  through 
the  mass  by  pumping  from  below  the  false  bottom,  and  returning 
it  to  the  top.  An  apparatus  similar  to  that  shown  in  Fig.  120  is 
sometimes  used. 

Hanks  of  yarn  are  often  dyed  by  suspending  from  sticks,  or  rods, 
laid  across  the  top  of  the  open  dye-vat,  which  has  a  false  bottom, 
under  which  the  heating  steam  is  introduced.  Turning  the  hanks 
by  hand  involves  much  labor,  and  machines  have  been  devised  in 
which  the  hanks,  weighted  at  the  lower  end  by  rollers  to  keep  them 
straight,  are  suspended  on  rollers  of  wood  or  porcelain,  which  are 
rotated  by  driving  gears.  Or  the  hanks  are  fixed  on  rods,  on  the  pe- 
riphery of  a  rotating  drum,  which  is  partly  submerged  in  the  dye-bath ; 
the  rods  are  revolved  slightly,  at  each  turn  of  the  drum,  so  the  skeins 
are  moved  frequently  during  the  dyeing.  The  apparatus  is  enclosed 
in  a  wooden  case,  to  confine  the  steam  and  heat,  and  prevent  too  much 
cooling  of  the  yarn  while  not  submerged. 

Much  yarn  is  dyed  while  wound  on  the  "  cops  "  or  spools  formed 
on  the  spinning  frames,  the  dye-liquor  being  forced  through  the  per- 
forated tubes  of  the  spools,  from  the  interior  to  the  exterior  of  every 
spool.  Yarn  in  warps  is  dyed  by  running  the  warp  over  numerous 
rollers  submerged  in  the  dye-liquor,  in  a  deep  vat. 

The  commercial  dyes  may  be  grouped,  according  to  the  method 
of  their  application  to  the  fibre,  into  eight  classes :  — 

I.  Direct  dyes,  yielding  full  colors  on  all  fibres  without  mordants. 

II.  Basic  dyes,  which  form  insoluble  tannates  and  require  mor- 
dants on  vegetable  fibres,  but  color  animal  fibres  without  mordants. 

III.  Acid  dyes,  which  require  no  mordant  on  animal  fibres,  but 
are  only  of  limited  use  with  vegetable  fibres,  mordanted  or  not. 

IV.  Mordant   dyes,    which   require   metallic   mordants   on   both 
animal  and  vegetable  fibres. 

V.  Acid-mordant   dyes,   which   will   dye   animal   fibres   directly, 
but  require  mordants  for  the  development  of  full  and  fast  colors. 

VI.  Sulphide   colors   which   dye   vegetable   fibres   from   alkaline 
baths  containing  sodium  sulphide  in  solution. 

VII.  Vat  dyes,  which  require  reduction  to  a  soluble  form  in  dilute 


532  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

alkaline  solution,  followed  by  reoxidation  of  the  dyestuff  on  the  fibre, 
to  develop  the  color. 

VIII.  Ingrain  colors,  which  are  produced  directly  from  their  con- 
stituents upon  the  fibre. 

I.  The  direct  dyes  are  soluble  colors  which  are  adsorbed  from 
solution  by  all  fibres,  although  the  adsorption  from  the  bath  is  usually 
not  very  complete.  These  dyes,  therefore,  tend  to  "  bleed  "  when 
washed,  but  this  same  property  makes  them  easy  to  dye  evenly, 
("  level  ")  on  the  goods,  as  they  readily  redissolve  from  a  point  where 
heavily  deposited  and  again  precipitate  on  less  heavily  colored  places. 
They  are  rather  fugitive  to  light,  and  are  affected  by  acids  and  alka- 
lies. By  after-treatment  with  certain  metallic  salts  (copper,  chro- 
mium, etc.)  the  fastness  to  light  and  washing  is  much  improved.  Those 
dyes  in  which  the  auxochrome  is  an  amino  group  may  be  diazotized 
and  "  developed  "  on  the  fibre,  with  phenols  or  amino-compounds,  and 
thus  their  fastness  can  be  increased. 

The  dye-baths  for  direct  colors  must  be  concentrated  color  solu- 
tions, and  do  not  exhaust  well,  hence  the  practice  of  using  standing 
baths  is  common,  a  certain  amount  of  dye  being  added  to  the 
bath  before  the  next  batch  of  goods  is  entered.  A  so-called  "  assist- 
ant "  is  usually  added  to  the  dye-bath  to  accelerate,  retard,  or  modify 
the  deposition  of  the  color ;  but  this  does  not  enter  into  combination 
with  the  color  (or  with  the  mordant  when  used  with  basic,  acid, 
or  other  dyes).  The  assistants  used  for  direct  dyes  are  Glauber's 
salt,  common  salt,  soda,  borax,  sodium  phosphate,  or  soap ;  these 
are  added  in  amounts  varying  from  5  to  50  or  more  per  cent  of  the 
weight  of  the  goods  to  be  dyed.  The  assistant,  when  a  neutral  salt, 
renders  the  dye  less  soluble  and  causes  more  complete  precipitation 
on  the  goods,  by  its  "  salting-out  effect  "  * ;  an  assistant  with  alkaline 
or  acid  reaction  is  more  generally  used  to  retard  the  deposition  by 
increasing  the  solubility. 

Wool  is  dyed  with  the  direct  dyes  by  boiling  in  neutral  or  slightly 
acid  (acetic  acid)  baths,  usually  with  the  addition  of  Glauber's  salt. 
As  a  rule  the  acetic  acid  is  not  added  until  the  dye-bath  is  nearly 
exhausted.  The  shades  produced  on  wool  are  tolerably  fast  to  acids, 
washing,  and  milling,  in  most  cases. 

Silk  is  seldom  dyed  with  direct  dyes,  but  may  be  colored  in  weak 
acid  (acetic,  tartaric,  citric,  or  sulphuric)  baths  of  "  boiled-off " 
liquor  (p.  494),  or  soap,  starting  at  about  40°  C.,  and  slowly  raising 
the  temperature  to  boiling. 

*  See  Nernst's  Theoretical  Chemistry,  p.  537. 


TEXTILE    INDUSTRIES  533 

Cotton  is  dyed  with  direct  colors  in  cold,  luke-Warm,  or  boiling 
baths,  containing  5  to  20  per  cent  Glauber's  salt,  and  3  to  5  per  cent 
soda-ash.  Sometimes  2  to  10  per  cent  common  salt  is  used  with,  or 
in  place  of,  the  Glauber's  salt.  Caustic  soda  and  soap  may  be  used 
in  the  bath  for  cold  dyeing.  After  dyeing  the  goods  are  worked  in 
a  solution  of  Turkey-red  oil,  or  this  may  be  added  to  the  dye-bath. 

Mixed  wool  and  cotton  goods  ("  unions  ")  are  often  colored  with 
such  direct  dyes  as  have  equal  affinity  for  the  two  fibres,  in  order 
that  the  shades  may  match.  Mixed  cotton  and  silk  goods  are  also 
dyed  with  direct  colors ;  since  some  of  them  do  not  color  silk  in  soap 
baths,  it  is  often  possible  to  dye  two  shades  on  such  mixed  goods 
producing  varieties  of  "  changeable  "  or  "  shot  "  effect.  Thus,  the 
cotton  may  be  dyed  in  a  soap-bath  and  the  silk  in  a  second  bath  of  an 
azo  or  acid  color,  which  has  no  effect  on  the  cotton. 

Diazotizing  the  dyed  goods  with  sodium  nitrite  in  acid  solution, 
washing  in  cold  water,  and  passing  directly  into  a  developing  bath 
containing  a  phenol,  or  amino-compound  (resorcinol,  /3-naphthol,  etc.), 
increases  the  fastness  greatly  of  many  of  these  colors  on  cotton.  Or 
the  dyed  goods  may  be  worked  in  a  diazotized  solution  of  an  ammo- 
body  (e.g.  p-nitraniline).  This  process  is  called  "  coupling'' 

After-treatment  with  metallic  salts,  by  working  the  dyed  and  rinsed 
goods  in  a  warm  acetic  acid  solution  of  copper  sulphate,  potassium 
bichromate,  or  chromium  fluoride,  is  much  employed  with  those 
dyes  containing  free  OH  or  COOH  groups,  to  increase  the  fastness. 
Many  of  the  direct  dyes  when  dyed  on  cotton  act  as  mordants  for 
basic  colors,  which  are  thus  used  for  "  topping  "  the  dyed  goods. 

II.  Basic  dyes  are  the  salts  of  colorless  bases  which  contain 
chromophorous  groups ;  the  color  does  not  appear  until  the  salt  is 
formed.  These  salts  are  not  appreciably  adsorbed  by  fibres,  except 
those  of  an  acid  character,  such  as  wool  and  silk,  in  which  case  an 
insoluble  color  salt  or  lake  of  the  base  with  the  fibre  itself  is  prob- 
ably formed;  the  acid  of  the  salt  in  the  dye-bath  is  largely  left  as 
free  acid  in  the  solution.  The  dyes  of  this  group  are  the  most  bril- 
liant known  (such  as  auramine,  rhodamine,  malachite  greens,  methy- 
lene  blue,  and  methyl  violets),  and  are  monogenetic ;  they  vary  much 
in  constitution  and  fastness,  but  in  general  are  rather  fugitive  and 
fade  through  the  action  of  light,  soap,  and  milling.  They  have  great 
tinctorial  power,  one  per  cent  usually  yielding  full  shades. 

These  dyes  are  usually  applied  in  neutral,  or  very  slightly  acid 
or  alkaline  baths.  Calcarious  water  is  bad  for  these  dyes,  as  it  pre- 


534  OUTLINES   OF    INDUSTRIAL   CHEMISTRY 

cipitates  the  color  bases  as  a  sticky,  curdy  mass,  which  adheres  to 
the  fibre,  causing  spots  and  unevenness.  The  commercial  dyestuffs 
are  usually  hydrochlorides,  but  some  are  acetates,  oxalates,  sulphates, 
or  double  salts  with  zinc  chloride. 

Wool  is  dyed  directly  in  a  boiling  bath,  by  the  basic  dyes,  for 
which  it  has  great  affinity,  as  above  explained,  but  since  with  few 
exceptions  the  colors  are  not  fast,  they  are  little  used  on  this  fibre. 
The  addition  of  a  little  acetic  or  sulphuric  acid,  or  alum,  to  the  bath 
moderates  the  color  deposition  by  rendering  the  dye  more  soluble, 
and  affords  more  level  dyeing.  Certain  basic  dyes  (e.g.  methyl  and 
benzaldehyde  greens)  have  no  affinity  for  wool  until  it  has  been 
mordanted  with  sulphur,  by  treating  with  sodium  thiosulphate  and 
sulphuric  acid,  or  alum.  A  few  of  the  basic  dyes  (e.g.  Victoria  blues) 
are  very  fast  to  milling  on  wool,  and  thus  find  considerable  use. 

Silk  is  largely  dyed  with  basic  dyes,  since  fastness  to  light  is  less 
important  with  this  material,  while  brilliancy  of  shade  is  much  de- 
sired. The  dyeing  is  done  in  neutral,  or  slightly  acid  or  alkaline 
baths,  containing  "  boiled-off  "  liquor,  or  neutral  soap  solution,  and 
the  temperature  is  usually  kept  between  70°  and  100°  C.  Some  acetic, 
tartaric,  or  citric  acid,  or  often  sulphuric  acid,  is  used  to  neutralize 
the  alkalinity  of  the  "  boiled-off  liquor,"  and  the  dyed  material, 
after  washing,  is  generally  "  brightened  "  by  passing  through  dilute 
acetic  or  tartaric  acid,*  hydroextracting,  and  drying  without  washing. 

Cotton  having  no  affinity  for  basic  dyes  requires  a  mordant  of 
an  acid  nature.  Tannin  (fixed  f  as  antimony,  tin,  or  iron  salt)  or 
Turkey-red  oil  (fixed  with  aluminum  acetate  as  the  insoluble  alu- 
minum salt  of  the  sulpho-acid)  are  the  usual  mordants  for  basic 
colors,  the  cotton  being  mordanted  first,  and  then  dyed  in  luke-warm 
baths,  which  are  slowly  heated  to  60°  C.  Higher  temperature  may 
cause  a  loss  of  brilliancy  in  shade.  The  goods  are  hydroextracted, 
or  evenly  wrung,  and  dried  without  washing.  Probably  the  basic 
dyestuff  combines  with  the  acid  of  the  mordant  to  form  an  insoluble 
or  at  least  highly  adsorbed  salt,  leaving  the  free  metallic  hydrate  in 
the  pores  of  the  fibre.  The  deposited  color  may,  however,  be  of  the 
nature  of  a  double  salt  of  the  color-base  and  the  metal. 

Union  goods  are  dyed  in  neutral  or  acid  bath,  the  cotton  having 
been  previously  mordanted  cold,  with  tannin  and  antimony,  which 

*  It  is  probable  that  a  part  of  the  dye  is  adsorbed  as  the  free  color-base,  espe- 
cially from  neutral  or  alkaline  dye-baths.  This  acid  serves  to  convert  all  to  the 
colored  salt. 

t  That  is,  rendered  insoluble. 


TEXTILE    INDUSTRIES  535 

have  no  effect  on  the  wool.  Silk  and  cotton  mixed  goods  are  first 
dyed,  so  that  the  silk  is  colored,  and  then  passed  through  cold  tannin 
solution  to  mordant  the  cotton  and  dyed  in  a  second  bath. 

III.  Acid  dyes  constitute  the  most  numerous  class  of  artificial 
coloring  matters.  All  are  dyed  on  animal  fibres  in  acid  baths,  and 
may  be  mixed  in  the  same  bath  for  compound  shades.  The  com- 
mercial dyestuffs  consist  of  alkali  or  lime  salts  of  the  color  acid, 
except  in  the  case  of  picric  acid,  which  is  used  in  the  free  state.  The 
color  acids  of  these  dyes  are  strongly  adsorbed  on  animal  fibres, 
(perhaps  due  to  interaction  with  the  amido-groups  of  the  fibre  sub- 
stance) but  are  not  appreciably  adsorbed  by  cellulose. 

The  acid  dyes  are  grouped,  according  to  their  constitution,  into 

(a)  Nitro  compounds. 

(6)  Sulphonated  basic  dyes. 

(c)  Azo  colors. 

(d)  Phthaleins. 

The  nitro-dyes  are  all  yellows  and  owe  their  acid  nature  and  col- 
oring properties  to  the  chromophorus  nitro-groups  present.  They 
usually  have  auxochromous  groups,  such  as  OH,  or  imido  (NH)  also. 

The  sulphonated  basic  dyes  are  derived  from  coloring  matters 
which  are  bases,  by  introducing  the  sulpho-group  (SO3H).  This  does 
not  materially  change  the  hue  of  the  basic  dye,  but  does  reduce  its 
tinctorial  power,  and  destroys  its  affinity  for  tannin  mordants. 

The'  azo  colors  contain  besides  the  chromophor  (azo-group) 
—  N  =  N  — ,  certain  auxochromous  groups,  either  OH  or  NH2. 
These  are  the  most  numerous  and  important  .of  the  acid  dyes,  and 
are  extensively  used  on  wool.  The  colors  are  fast  on  wool  to  light 
and  acids,  and  fairly  so  on  silk. 

The  phthaleins  comprise  certain  brilliant  pinks  and  reds  (e.g. 
the  eosins)  much  used  for  silk.  They  are  dyed  from  very  weak  (acetic) 
acid  baths. 

Related  to  the  acid  dyes  are  the  acid-chrome  colors,  which  are 
dyed  on  wool  from  acid  baths,  and  then  fixed  or  developed  by  an 
after-treatment  with  chrome  mordants. 

Wool  is  dyed  with  acid  colors  by  boiling  in  baths  containing  free 
sulphuric  acid  and  10  to  20  per  cent  Glauber's  salt.  The  former  sets 
free  the  color-acid  and  reduces  its  solubility  by  driving  back  its 
dissociation  in  accordance  with  the  law  of  mass  action,  while  the 
latter  acts  as  a  restraining  assistant,  and  promotes  level  dyeing  by 
driving  back  the  dissociation  of  the  sulphuric  acid,  thus  decreasing 


536  OUTLINES   OF    INDUSTRIAL   CHEMISTRY 

both  the  amount  of  color-acid  set  free,  and  the  lowering  of  its  solubility. 
Acetic  or  formic  acid  may  be  used  in  place  of  the  sulphuric,  and  being 
weaker,  promote  level  shades,  though  their  greater  cost  lessens  their 
use.  By  adding  the  acid  a  little  at  a  time  during  the  boiling,  the 
color-acid  is  liberated  gradually  and  level  dyeing  is  facilitated.  The 
use  of  ammonium  acetate  in  the  dye-bath  is  advantageous,  since  it 
hydrolyzes  slowly  in  the  boiling  liquor,  the  ammonia  volatilizing  and 
setting  free  its  acid,  which  then  decomposes  the  dyestuff  and  the 
color-acid  is  deposited  on  the  fibre.  In  the  case  of  the  alkali  blues, 
the  color-acid  is  insoluble  in  water  but  its  alkali  salt  dissolves  readily, 
giving  a  colorless  solution  with  borax  or  soda.  The  wool  on  boiling 
in  this  bath  is  impregnated  with  the  alkaline  solution  but  shows  no 
color ;  on  passing  into  an  acid  bath,  the  alkali  salt  is  decomposed,  and 
the  free  color-acid  develops  on  the  fibre  as  a  deep-blue  color. 

Silk  is  dyed  with  acid  dyes  in  a  bath  containing  a  large  quantity 
of  "  boiled-off  "  liquor,  which  is  made  slightly  acid  by  acetic  or  formic 
acid.  The  temperature  is  kept  between  70°  and  90°  C.,  since  boiling 
lessens  the  affinity  of  the  silk  for  the  dye.  After  dyeing  and  washing, 
the  silk  is  "  brightened  "  *  in  dilute  acid  and  dried  without  washing. 

Cotton  and  other  vegetable  fibres  have  no  affinity  for  acid  dyes, 
and  even  mordanting  with  alum  and  soda,  or  stannic  chloride,  fol- 
lowed by  basic  alum,  does  not  produce  satisfactory  results.  The 
colors  are  not  fast  to  washing  nor  to  light. 

IV.  The  mordant  dyes  are  substances  not  adsorbed  by  fibres, 
but  strongly  adsorbed  on  various  weak,  insoluble  metallic  hydroxides, 
or  in  some  cases  perhaps  forming  definite  salts  with  them.  In  either 
case  the  product  of  the  condensation  of  the  dye  on  the  hydrate  is 
called  a  color-lake.  They  yield  colors  which  are  generally  fast  to 
washing,  soaping,  milling,  and  light.  They  comprise  a  great  variety 
of  coloring  matters,  both  of  natural  and  artificial  origin,  which  in 
view  of  their  nature  must  be  dyed  on  all  fibres  by  the  aid  of  metallic 
mordants.  Many  of  these  dyes  are  polygenetic. 

The  mordanted  goods  are  passed  into  a  dye-bath,  usually  con- 
taining the  color  alone ;  but  in  the  case  of  certain  natural  dyewoods, 
the  mordant  and  dye  may  be  applied  in  the  same  bath;  in  others, 
the  goods  are  first  impregnated  with  the  dye,  and  the  color  fixed  on 
the  fibre  by  subsequent  treatment  in  the  mordant  bath  (dyeing  and 

*  See  p.  534.  In  this  case  it  is  possible  that  the  color-acid  forms  with  the 
fibre  a  less  highly  colored  salt ;  the  acid  treatment  decomposes  this,  leaving  all  the 
color  in  the  acid  form. 


TEXTILE    INDUSTRIES  537 

saddening  method).  Mordant  colors  may  be  mixed  in  the  same  dye- 
bath,  provided  the  same  mordant  is  used  for  each. 

The  mordant  oxides  chiefly  employed  are  those  of  aluminum, 
chromium,  iron,  and  tin.  The  mordant  colors  themselves  serve  as 
mordants  for  fixing  basic  dyes,  hence  the  latter  are  often  used  to 
brighten  the  shade  of  the  former.  Many  of  the  artificial  mordant 
colors  are  nearly  insoluble  in  water,  and  if  once  dried  are  difficult  to 
again  dissolve  in  the  dye-bath ;  these  are  often  sold  as  "  pastes," 
containing  from  60  to  80  per  cent  of  water. 

Cotton  is  always  mordanted  in  separate  baths  before  dyeing  with 
these  colors.  Cotton  mordanting  with  chromium  is  difficult,  but  the 
use  of  basic  chromium  acetates,  chlorides,  etc.,  by  Koechlin's  method 
(p.  514),  makes  it  possible.  Often  cotton  is  prepared  with  Turkey- 
red  oil  before  mordanting  with  chromium.  Aluminum  mordants  are 
largely  used  on  cotton,  but  iron  and  tin  less  frequently.  Turkey- 
reds,  alizarin  red,  ccerulein,  and  other  alizarin  colors,  logwood  blacks, 
and  catechu  browns  are  the  chief  mordant  colors  on  cotton. 

For  centuries  Turkey-reds  have  been  produced  on  cotton  by  the 
aid  of  madder,  oil,  and  aluminum  salts;  this  gives  a  brilliant  red, 
very  fast  to  light,  washing,  or  friction,  and  to  chemical  agents.  By 
the  old  process,  about  four  weeks  was  required  for  the  dyeing,  but  the 
new  process  reduces  the  time  to  about  three  days.  Madder  has  been 
completely  displaced  by  artificial  alizarin  made  from  anthracene 
(p.  524).  The  Turkey-red  process  on  cotton  is  complicated,  and 
requires  a  special  mordanting  of  the  goods.  In  outline  the  process  is 
as  follows :  The  bleached  cotton  (p.  506)  is  first  oiled  by  steeping 
or  padding  in  a  10  or  15  per  cent  solution  of  neutralized  Turkey-red 
oil  (p.  362)  in  water.  The  excess  of  oil  is  squeezed  out  and  the  goods 
"  aged,"  or  steamed,  at  about  5  pounds  pressure,  to  render  the  oil 
insoluble  and  to  fix  it  on  the  fibre.  Oxidation  and  probable  polymer- 
izing of  the  oleic  acid  and  other  constituents  of  the  oil  occur,  and 
substances  are  fixed  on  the  fibre  which  combine  with,  and  assist  in 
fixing,  the  metallic  mordants,  and  perhaps  form  a  varnish  coat  over 
the  color-lake,  protecting  it  from  air  and  chemicals,  thus  increasing 
the  fastness  and  lustre  of  the  dyed  fabric.*  The  goods  are  mordanted 
by  working  in  a  tepid  solution  of  aluminum  acetate  (red  liquor),  or 
basic  aluminum  sulphate,  the  oxide  being  fixed  by  aging;  or  in  a 
bath  of  powdered  chalk  and  water,  or  of  sodium  phosphate,  which 
removes  the  excess  of  oil.  Formerly  sodium  arsenate  was  used  for 

*  The  oiled  cotton  may  be  steeped  in  a  decoction  of  sumach,  but  this  is  not 
essential,  and  is  generally  omitted. 


538  OUTLINES   OF    INDUSTRIAL    CHEMISTRY 

this  "  dung-bath,"  and  afforded  very  light  shades.  For  dyeing,  the 
mordanted  cotton  is  first  worked  in  a  cold  bath  of  alizarin  suspended 
in  water,  containing  some  lime,  calcium  being  essential  to  the  forma- 
tion of  the  color-lake ;  hard  water,  free  from  iron,  is  preferred  for  this 
bath,  but  if  not  available,  powdered  chalk  or  calcium  acetate  is  added. 
The  bath  is  then  very  slowly  heated  to  70°  C.,  where  it  is  kept  until 
the  dye  is  all  deposited.  The  cotton  at  this  time  is  a  dull  red,  and  to 
develop  the  brilliant  shade,  the  goods  are  steamed  at  about  15  pounds 
pressure  for  an  hour.  Sometimes  they  are  oiled  a  second  time  before 
steaming.  Then  they  are  thoroughly  washed  with  soap,  two  or  three 
soapings  being  given ;  stannous  chloride  is  often  added  to  the  soap 
bath  to  increase  the  brilliancy.  It  is  very  essential  that  neither  the 
mordants  nor  the  dye-bath  be  contaminated  with  the  slightest  trace 
of  iron  in  any  form.  Turkey-reds  are  dyed  by  several  other  processes, 
which  cannot  be  considered  here. 

Various  shades  of  violet,  lilac,  and  purple  are  dyed  on  cotton 
with  alizarin,  by  mordanting  with  ferrous  acetate  (pyro-iron,  p.  309) 
instead  of  red  liquor,  and  usually  omitting  the  oiling.  A  tannin-iron 
mordant  affords  purple  blacks,  while  mixtures  of  iron  and  aluminum 
mordants  give  shades  from  claret  red  to  chocolate.  Other  alizarin 
colors  are  dyed  on  cotton  and  linen  with  aluminum,  chromium,  and 
iron  mordants.  The  methods  vary  somewhat  with  each  dye,  and 
must  be  sought  for  in  special  works  on  dyeing. 

Linen  is  dyed  with  alizarin  in  the  same  way  as  cotton.  The 
fastness  of  Turkey-red  to  washing  and  soap  makes  it  especially 
valuable  for  dyeing  linen  yarn,  which  is  then  woven  into  figured 
wash-goods. 

Logwood  yields  blacks  and  grays  on  cotton  mordanted  with  tannin 
and  iron,  which  were  formerly  very  important  because  of  their  cheap- 
ness, but  the  new,  fast,  vat  dyes  (p.  541)  and  the  sulphur  colors 
(p.  540)  have  largely  replaced  them,  as  well  as  most  other  mordant 
dyes  for  cotton  dyeing. 

Wool  is  largely  dyed  with  mordant  colors  because  of  their  fastness 
to  light,  chemicals,  milling,  and  washing.  The  fibre  must  be  well 
scoured  to  remove  oil  or  grease  before  mordanting,  otherwise  uneven 
dyeing  will  result.  The  mordants  used  on  wool  are  mainly  chromium 
salts ;  aluminum  salts  find  some  use  with  the  alizarin  colors.  The 
wool  is  boiled  with  2  to  3  per  cent  (of  the  weight  of  the  goods)  of 
potassium  bichromate  with  the  addition  of  1  per  cent  of  sulphuric 
acid ;  often  cream  of  tartar  is  used  with  bichromate.  Chromium 
fluoride  (3  per  cent)  with  oxalic  acid  is  also  used  for  wool.  After 


TEXTILE   INDUSTRIES  539 

aging  for  several  hours  in  a  dark  place  to  fix  the  oxide,  the  goods 
are  washed  and  at  once  dyed  without  drying. 

The  dye-bath  usually  contains  only  water  and  the  dyestuff,  but  with 
some  alizarins  a  little  acetic  acid  is  added.  The  goods  are  entered 
with  the  bath  at  about  40°  C.,  and  the  temperature  slowly  raised  to  the 
boiling  point  in  about  an  hour ;  boiling  is  continued  for  another  hour 
or  more. 

Some  alizarin  colors  are  applied  with  the  mordant  (potassium 
bichromate  or  chromium  fluoride)  and  the  dye  together  in  the  same 
bath  ;  the  goods  are  entered  in  the  cold  bath,  which  is  slowly  raised  to 
boiling.  This  "single  bath"  process  wastes  color  (due  to  oxidation) 
and  produces  less  fast  dyeings. 

Silk  is  rarely  dyed  with  mordant  colors,  since  the  hues  are  less  bril- 
liant than  those  obtained  with  substantive  dyes,  and  the  latter  are 
cheaper  and  sufficiently  fast.  Silk,  mordanted  with  chromium 
chloride,  or  with  basic  aluminum  sulphate  or  acetate,  fixed  with 
silicate  of  soda  solution,  may  be  dyed  in  a  bath  of  "boiled  off"  liquor, 
neutralized  or  slightly  acidified  with  acetic  acid.  The  goods  are 
entered  in  the  cold  bath,  which  is  very  slowly  heated  to  boiling  and 
held  at  that  temperature  for  an  hour.  After  washing  the  dyed  goods 
are  boiled  in  soap  liquor  and  brightened  in  dilute  acetic  acid  at  30°  C. 

V.  Acid-mordant  dyes  (acid-chrome  colors)  are  chiefly  used  on 
wool,  and  to  a  small  extent  on  silk ;  they  are  not  applied  to  cotton. 
These  dyestuff s  are  usually  sulphonated  azo-derivatives  of  salicylic 
acid,  or  of  orthoaminophenol  bodies ;  some  are  derived  from  anthra- 
cene or  pyrogallol.  They  may  be  used  as  acid  dyes  in  the  usual  way, 
but  faster  and  better  colors  are  developed  when  they  are  used  with 
mordants,  chiefly  chromium.  These  dyes  include  a  full  series  of 
colors  from  reds  to  violets  and  also  browns,  grays,  and  blacks.  They 
are  especially  useful  for  loose  wool  and  yarn  because  of  their  fastness 
to  milling  and  light. 

Wool  is  dyed  by  heating  to  boiling  in  a  bath  containing  a  little  free 
acid  (1  to  4  per  cent  sulphuric,  acetic,  or  formic  acid)  and  5  to  10  per 
cent  of  Glauber's  salt.  After  boiling  until  the  color  is  all  deposited 
(which  is  aided  by  the  gradual  addition  of  a  little  more  acid),  the  goods 
are  lifted  from  the  bath,  and  potassium  bichromate  or  other  metallic 
salt  added,  the  wool  reentered,  and  the  boiling  continued  another  half 
hour.  By  using  a  mixture  of  neutral  potassium  chromate  and  am- 
monium sulphate  (meta-chrome  mordant)  instead  of  the  bichromate, 
a  more  gradual  and  even  deposition  of  color  is  secured,  owing  to  the 


540  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

slow  liberation  of  the  acid  from  the  ammonium  salt  during  the  boiling. 
Other  special  modifications  of  the  process  are  in  use. 

Silk  is  dyed  like  wool  with  these  colors,  but  often  chromium  fluoride 
and  acetic  acid  are  used  in  the  after-chroming. 

VI.  The  sulphide  dyes  constitute  a  large  and  important  group  of 
colors,  yielding  fast  dyeings  on  cotton  and  other  vegetable  fibres. 
They  are  made  by  fusing  sulphur  or  sodium  sulphide  with  various  aro- 
matic bodies  containing  nitro-,  amino-,  or  imino-groups.  The  constitu- 
tion of  these  colors  is  not  fully  known,  but  they  probably  contain  free 
sulphur  and  mercaptans.  They  are  insoluble  in  water,  but  dissolve 
in  alkaline  reducing  solutions,  especially  sodium  sulphide,  sodium 
hydrosulphite,  or  caustic  soda  and  glucose.  These  dyestuffs  form 
insoluble  products  with  the  oxygen  of  the  air  and  precipitate;  this 
necessitates  a  strongly  reducing  bath,  and  also  keeping  the  goods 
entirely  submerged.  Since  the  sulphide  acts  upon  copper,  forming 
oxygen-carrying  copper  salts,  the  dye-vats  must  be  made  of  wood  or 
iron,  and  no  brass  or  copper  fittings  should  touch  the  dye  liquor. 

The  commercial  dyestuffs  are  sold  under  trade  names  adopted  by 
the  different  makers,  such  as  Immedial,  Katigene,  Kryogene,  Pyro- 
gene,  Sulphur,  Thiogene,  Thion,  Thionol,  and  others.  They  are 
little  used  for  wool  and  silk  dyeing,  since  the  alkaline  bath  is  inju- 
rious to  these  fibres ;  but  the  addition  of  glucose  to  the  bath  protects 
these  fibres  to  some  extent,  and  thus  "  unions  "  may  be  dyed  in  the 
presence  of  glucose.  The  addition  of  glue  to  the  bath  prevents  silk 
from  taking  the  color,  and  thus  mixed  silk  and  cotton  goods  can  be 
dyed  in  two-color  effects. 

Cotton  and  linen  are  dyed  with  sulphide  colors,  without  previous 
preparation.  The  bath  is  made  up  with  the  dyestuff  and  an  equal 
weight  of  sodium  sulphide,  dissolved  in  hot  water,  to  which  is  then 
added  about  5  per  cent  of  soda  and  10  to  50  per  cent  of  Glauber's 
salt,  or  common  salt.  Turkey -red  oil,  or  monopol  soap  or  oil, 
glue,  and  glucose  may  also  be  added.  The  bath  is  heated  to  35°  to 
75°  C.,  depending  on  the  color  used.  Most  of  these  dyes  work  well 
in  cold  baths.  The  goods  should  be  kept  entirely  submerged  in  the 
liquor,  to  prevent  irregular  color  deposition.  When  removed  from  the 
bath,  the  goods  are  rapidly  freed  from  excess  liquor  by  squeeze-rolls 
or  centrifugal  wringing,  to  afford  level  shades.  Sometimes  the  goods 
are  immediately  rinsed,  and  in  other  cases  a  short  exposure  to  the 
air  is  desirable  before  rinsing. 

Generally  the  dyed  goods  receive  some  kind  of  after-treatment, 


TEXTILE    INDUSTRIES  541 

as  with  metallic  salts,  such  as  a  mixture  of  copper  sulphate  and  po- 
tassium bichromate,  with  a  little  acetic  acid,  for  most  colors ;  but  for 
blacks,  no  copper  salts  should  be  used,  as  they  are  prone  to  assist 
oxidation  of  the  sulphur  in  the  dye  by  catalysis,  thus  forming  sul- 
phuric acid,  which  weakens  the  fibre  after  a  time.  A  further  after- 
treatment  of  the  dyed  material  with  soda,  soap,  sodium  acetate,  or 
formate  is  recommended  to  prevent  the  subsequent  "  tendering  "  of 
the  goods.  Tendering  does  not  become  obvious  for  several  weeks  or 
months  after  the  goods  are  dyed,  and  has  caused  much  deterioration 
of  goods  in  storage. 

Some  of  these  colors  (Immedial  and  Kryogene  blues  and  others) 
are  improved  by  developing,  by  steaming  for  half  an  hour,  or  by  aging 
several  hours  in  a  warm,  damp  atmosphere. 

VII.  The  vat  dyes  constitute  an  important  group  of  dyestuffs,  of 
which  indigo  (p.  521)  was  for  long  the  only  one  known ;  but  recently 
numerous  others  have  been  synthesized.  The  vat  colors  are  readily 
reduced  in  alkaline  solutions,  and  become  soluble,  but  on  oxidation, 
or  exposure  to  the  air,  the  -insoluble  color  is  reprecipitated.  The 
solution  of  reduced  color  is  called  the  "  vat,"  and  may  be  prepared 
in  various  ways.  Some  of  them  are  derivatives  of  indigotine  (the  in- 
digoids)  and  others  are  anthracene  derivatives.  The  indigotine  deriva- 
tives can  be  applied  to  both  animal  and  vegetable  fibres  in  the  hydro- 
sulphite  vat  and  as  they  may  be  applied  to  vegetable  fibres  in  the 
presence  of  sodium  sulphide,  they  are  often  used  in  the  same  bath 
with  sulphide  colors  for  compound  shades  ;  but  the  anthracene  deriva- 
tives require  strong  alkaline  (caustic  soda)  vats,  and  are  only  suitable 
for  cotton. 

Dyeing  with  natural  indigo  has  been  practised  in  India,  Egypt, 
and  other  eastern  countries  for  centuries,  by  methods  very  similar 
to  some  now  in  use.  It  was  not  until  the  synthesis  of  artificial  indigo, 
however,  that  the  other  dyes  of  this  group  were  produced.  It  has 
recently  been  shown  that  the  ancient  Tyrian  purple  obtained  from  a 
mollusk  (Murex)  is  probably  identical  with  one  of  these  vat  colors 
(a  dibrom-indigotine).  The  commercial  vat  dyes  besides  indigo  are 
the  various  halogen  derivatives  of  indigotine,  methyl  and  tolyl  indigo- 
tine, ciba  colors,  thioindigos,  algole  dyes,  helindone  dyes,  indanthrene 
dyes,  and  others. 

Wool  is  dyed  with  indigo  in  the  old  fermentation  vat,  and  more 
largely  now  by  the  use  of  the  hydrosulphite  vat.  Several  varieties  of 
the  fermentation  vat  are  used,  the  woad  yat  being  most  important 


542  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

for  cloth.  In  this,  a  mixture  of  woad  with  water  is  incorporated 
with  bran,  madder,  finely  ground  indigo,  and  some  lime.  A  butyric 
fermentation  sets  in  and  hydrogen  is  evolved  and  reduces  the  indigo 
to  indigo  white,  which  dissolves  in  the  alkaline  liquor.  The  addition 
of  more  lime  checks  the  fermentation,  while  adding  bran  accelerates 
it.  The  wool,  wet  in  warm  water,  and  wrung,  is  submerged  in  the  vat 
and  worked  for  some  time.  After  wringing  to  remove  excess  indigo 
solution,  the  goods  are  exposed  to  the  air  to  oxidize  the  indigo  white. 
For  dark  shades  the  goods  are  returned  to  the  vat  two  or  three 
times. 

The  hydrosulphite  vat  is  much  used  for  rapid  dyeing  of  large 
quantities  of  material,  or  where  dyeing  is  carried  on  irregularly,  and 
subject  to  frequent  interruptions.  A  stock-vat  is  first  prepared  *  by 
suspending  20  Ibs.  of  indigo  (artificial  20  per  cent  paste)  in  2  gallons  of 
water,  and  stirring  in  4  Ibs.  of  anhydrous  hydrosulphite  (p.  60). 
After  10  minutes,  4  pints  of  caustic  soda  liquor  (76°  Tw.)  are  added 
and  the  mixture  heated  to  50°  C.  Solution  takes  place  rapidly, 
forming  a  clear  greenish  yellow  liquid. 

The  dye-vat  is  prepared  *  by  adding  to  1000  gallons  of  water, 
warmed  to  50°  C.,  about  J  gallon  of  ammonia,  9  ounces  hydrosulphite 
powder,  and  3|  gallons  of  a  solution  of  glue  (1  :  10).  The  required 
amount  of  stock  indigo  solution  is  then  added,  stirred  well,  and  the 
goods  at  once  entered,  and  worked  about  20  minutes.  After  squeez- 
ing out  excess  liquor,  the  goods  are  exposed  to  the  air  to  oxidize  the 
indigo,  and  then  well  washed.  Often  the  goods  are  first  dyed 
(bottomed)  with  a  red  dye,  as  barwood  or  diamine  reds,  before  the 
indigo  dyeing.  This  may  be  followed  by  "  topping  "  with  some  red 
or  violet,  to  add  "  bloom  "  to  the  color. 

Cotton  is  dyed  with  indigo  in  several  types  of  vat,  which  are, 
however,  more  strongly  alkaline  than  for  wool,  and  as  a  rule  are 
worked  cold.  The  hydrosulphite  vat,  similar  to  that  for  wool  above, 
is  largely  used  for  piece-goods,  with  jiggers,  and  in  dyeing  machines 
for  yarn  and  loose  cotton. 

The  zinc-lime  vat,  suitable  for  hanks  and  piece-goods,  is  prepared  by 
mixing  the  indigo  (20  per  cent  paste)  with  zinc-dust  and  quick-lime,  sus- 
pended in  water,  and  heating  to  about  55°  C.,  for  3  to  5  hours.  When 
the  liquor  is  a  clear  yellow  color,  it  is  decanted  from  the  sediment 
into  the  dye-vat  containing  more  water  and  a  little  lime  and  zinc- 
dust.  The  wet  goods  are  then  entered  and  worked  in  the  liquor. 

*  From  Pocket  Guide  to  the  Application  of  the  Dyestuffs  of  the  Badische  Anilin- 
und  Soda-Fabrik.  Ludwigshafen  am  Rhine. 


TEXTILE    INDUSTRIES  543 

The  bath  may  be  replenished  with  more  reduced  indigo  liquor,  and 
thus  kept  in  operation  for  subsequent  lots. 

The  copperas  vat,  also  used  for  yarn  and  piece-goods,  is  prepared 
by  mixing  indigo  (paste)  with  wrarm  (50°  C.)  milk  of  lime,  to  which 
is  added  a  solution  of  copperas  (ferrous  sulphate),  and  the  whole 
allowed  to  stand  5  or  6  hours,  with  occasional  stirring.  The  ferrous 
hydroxide,  precipitated  in  the  presence  of  excess  calcium  hydroxide 
and  the  indigo,  reduces  the  latter.  The  reactions  are  probably  as 
follows :  — 

FeS04  +  Ca(OH)2  =  Fe(OH)2  +  CaSO4. 
C16H10N202  +  2  Fe(OH)2  +  2  H2O  =  C16H12N2O2  +  2  Fe(OH)3. 

The  indigo  white  then  dissolves  in  the  excess  milk  of  lime  to  form  a 
brownish  yellow  solution,  which  after  settling  is  ready  for  use.  There 
is  much  sediment  produced  in  this  vat,  and  considerable  dyestuff  is 
lost,  probably  by  adsorption  on  the  ferric  hydroxide;  but  the  vat  is 
easy  to  set,  and  keeps  in  good  order. 

Fermentation  vats  are  also  used  for  cotton,  especially  in  India, 
Egypt,  China,  and  other  eastern  countries. 

VIII.  The  ingrain  colors  comprise  a  number  of  insoluble  sub- 
stances, which  are  produced  directly  on  the  fibres,  by  saturating  the 
goods  with  one  or  more  of  the  constituents  of  the  color,  and  then  caus- 
ing a  suitable  chemical  reaction  to  take  place,  by  subjecting  the  ma- 
terial to  treatment  with  the  other  constituents,  to  produce  the  in- 
soluble colored  precipitate  within  the  pores  of  the  fibre.  The  more 
important  of  these  colors  are  aniline  black,  certain  azo  bodies  (as  para 
reds  and  browns,  azo-blues,  etc.),  and  the  mineral  dyes.  Each  of 
these  colors  is  produced  by  a  special  process,  and  they  are  chiefly  im- 
portant as  cotton  dyes. 

Aniline  black  consists  of  an  insoluble  black  pigment  produced  by 
the  oxidation  of  aniline  in  acid  solution,  by  various  agents  such  as 
chlorate,  chromates,  ferrocyanides,  and  salts  of  copper,  vanadium, 
cerium,  etc.,  acting  as  catalyzers  to  aid  oxidation  by  air.  It  is  used 
only  on  cotton,  and  much  care  is  necessary  to  prevent  weakening  of 
the  fibre.  It  is  also  very  liable  to  turn  greenish  hue  in  time.  Much 
investigation  *  has  been  carried  on  to  determine  the  composition  of 
the  black,  which  is  yet  somewhat  uncertain. 

*  Green  and  Woodhead,  Trans.  Chem.  Soc.,  1910,  223.  Willstatter  and  Moore, 
Ber.,  1907,  2665  ;  1909,  4118.  Ibid.,  J.  Soc.  Dyers  and  Col.,  1908, 4.  Marsden,  J. 
Soc.  Dyers  and  Col.,  1908,  9.  Nietzki,  Ber.,  1878,  1094.  Ibid.,  Chemie  d.  Organ. 
Farbstoffe,  5th  ed.  p.  267. 


544  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

The  methods  of  producing  aniline  black  industrially  may  be 
grouped  under  the  headings :  (a)  Dyed  blacks;  (b)  Aged  blacks; 
(c)  Steam  blacks. 

Dyed  blacks  (one-bath  blacks),  chiefly  produced  on  yarn  by  working 
in  a  solution  containing  aniline  hydrochloride,  bichromate  of  soda, 
hydrochloric  and  sulphuric  acids,  and  water,  while  slowly  heating 
nearly  to  boiling,  are  not  very  well  fixed  and  the  color  is  liable  to 
"  rub.'*  By  steaming  the  dyed  goods,  the  fastness  is  improved. 
This  method  is  less  injurious  to  the  strength  of  the  fibre  than  is  the 
aging  process. 

Aged  black  is  produced  on  both  yarn  and  piece-goods,  by  padding 
in  a  solution  of  aniline  salt  an  oxidizing  agent  (sodium  chlorate) 
and  a  catalyzer  (copper  or  vanadium  salt,  or  a  ferrocyanide).  The 
material  is  dried  and  "  aged  "  for  six  or  eight  hours,  by  passing  slowly 
through  an  aging-room  in  which  the  air  is  moist  and  the  tempera- 
ture is  kept  at  45°  to  50°  C.  The  goods  acquire  a  dark,  greenish 
black  color  in  the  ager,  and  this  is  converted  to  a  fast  black,  by  chrom- 
ing (without  washing)  for  15  minutes  in  a  warm  solution  of  bichro- 
mate containing  a  little  sulphuric  acid.  Then  the  goods  are  soaped, 
rinsed,  and  dried.  After  padding  and  during  the  aging,  the  goods 
must  be  carefully  protected  from  drops  of  water  (condensed  moisture, 
wet  hands,  etc.)  and  from  alkali,  or  spots  will  be  produced.  The 
aging  process  is  liable  to  weaken  the  fibre,  and  if  not  carefully  watched 
may  ruin  the  goods.  In  Green's  process,*  atmospheric  air  is  the 
oxidizing  agent,  acting  with  cuprous  chloride  as  catalyzer,  and  with 
a  paradiamine  in  the  padding  liquor.  Formic  acid  is  used  in  place  of 
sulphuric  to  reduce  the  risk  of  tendering  the  fibre. 

Steam  blacks  are  produced  by  padding  in  a  liquor  containing  aniline 
salt,  sodium  chlorate,  and  potassium  ferrocyanide,  after  which  the 
goods  are  dried  and  steamed  for  three  minutes,  then  chromed  and 
soaped.  These  blacks  are  less  apt  to  injure  the  fibre,  but  the  method 
is  expensive. 

The  insoluble  azo  dyes  are  developed  on  the  fibre  by  first  impreg- 
nating the  goods  with  a  phenol  (j8-naphthol)  solution,  and  then  pass- 
ing into  a  cold  bath  of  a  diazo-compound,  whereby  the  color  is  pro- 
duced on  the  fibre.  It  is  essential  to  keep  the  diazotized  bath  as  cool 
as  possible,  and  this  is  often  done  by  putting  ice  into  the  bath  (hence 
the  name  "  ice-colors,"  sometimes  applied  to  these  dyes).  The  color 

*  J.  Soc.  Dyers  and  Col.,  1908,  231 ;  1909,  191. 


TEXTILE    INDUSTRIES  545 

is  produced  immediately  as  the  goods  enter  the  developing  bath,  and 
then  they  pass  at  once  to  the  washing  machines. 

The  most  important  of  these  colors  is  par anitr aniline  red,  produced 
from  /3-naphthol  and  diazotized  p-nitraniline.  It  is  a  fast  and  brilliant 
red,  used  as  a  substitute  for  Turkey-red  (p.  537).  Azo-blues  are 
obtained  with  /3-naphthol  and  dianisidine,  with  subsequent  treatment 
with  copper  salts.  Chloranisidine  yields  fast  scarlets. 

The  mineral  dyes  are  produced  on  the  fibre  by  saturating  it  with  a 
solution  of  a  metallic  salt,  and  passing  into  a  second  solution,  which 
decomposes  the  first  salt,  forming  a  colored  precipitate.  The  most 
important  colors  are  the  following :  — 

Iron  buff  or  Nankin  yellow,  which  consists  of  ferric  hydroxide. 
It  is  dyed  on  cotton  by  steeping  the  goods  in  a  solution  of  iron  salt 
(basic  ferric  sulphate,  ferric  nitrate,  or  copperas),  and  the  color  de- 
veloped by  treatment  with  calcium  hydroxide  solution,  or  caustic 
soda,  or  soda-ash,  as  in  mordanting  (p.  515). 

Chrome  green  can  be  formed  on  cotton  by  processes  similar  to 
those  used  for  mordanting  with  chromium  salts  (p.  514).  It  is  not 
very  important.  Khaki  is  a  greenish  brown  produced  by  the  simul- 
taneous precipitation  of  chromium  and  ferric  hydroxides  on  the  fibre. 
The  material  is  padded  in  a  mixture  of  chromium  and  ferrous  acetates, 
or  chrome  alum  and  ferric  chloride,  dried,  and  steamed.  The  cloth 
is  then  boiled  in  a  solution  of  soda-ash  containing  some  caustic  soda 
to  complete  the  precipitation. 

The  color  is  very  fast  to  light,  but  leaves  the  goods  stiff  and  harsh. 
Close  imitations  of  this  color  are  obtained  with  some  of  the  sulphide 
browns,  and  with  certain  indanthrene  dyes. 

Chrome  yellow  is  dyed  on  cotton  by  soaking  in  lime-water  and 
after  wringing,  passing  into  a  solution  of  basic  lead  acetate  or  nitrate. 
Repeat  the  lime-water  treatment,  wring,  and  work  in  a  solution  of 
sodium  bichromate.  Finally  the  goods  are  rinsed  in  dilute  hydro- 
chloric acid  (1 : 300),  washed,  and  dried.  The  shade  can  be  light- 
ened by  adding  zinc  sulphate  to  the  bichromate  solution.  The 
color  is  fast  to  light,  soap,  and  weak  acids,  but  is  turned  red  by  alka- 
lies, and  brown  or  black  by  sulphuretted  hydrogen.  The  goods  are 
heavily  weighted  by  this  process. 

Manganese  brown,  or  bronze,  consists  of  the  hydrated  peroxide  of 
manganese,  and  is  only  produced  on  cotton.  The  goods  are  steeped 
in  neutralized  manganese  chloride,  and  passed  through  a  hot,  dilute 
solution  of  caustic  soda,  to  which  some  sodium  hypochlorite  has  been 


546  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

added.  Precipitation  and  oxidation  occur  simultaneously,  and  a  full 
neutral  brown  is  developed.  A  mixture  of  potassium  permanganate 
and  soda-ash  in  solution  can  also  be  used  as  the  developing  bath. 
The  color  is  fast  to  light,  soap,  alkalies,  and  weak  acids. 

Prussian  blue  is  chiefly  dyed  on  silk  and  cotton,  especially  as  a 
base  or  ground  color,  upon  which  blacks  or  other  dark  colors  can  be 
dyed.  On  silk,  Prussian  blue  is  dyed  in  the  process  of  weighting, 
the  material  being  worked  in  a  solution  of  basic  ferric  sulphate, 
and  the  iron  hydroxide  formed  by  treatment  in  a  soap  bath  containing 
soda.  The  process  is  repeated  several  times,  and  the  material  then 
passed  into  an  acidulated  bath  of  potassium  ferrocyanide.  If  the 
blue  is  to  remain  as  the  final  color,  the  goods  are  softened  in  a  bath 
of  olive  oil  and  a  little  sulphuric  acid. 

Cotton  is  first  dyed  an  iron  buff  (p.  515)  and  then  passed  into  a 
dilute  sulphuric  acid  solution  of  ferrocyanide.  By  repeating  the 
process  deeper  shades  can  be  attained.  The  color  may  serve  as  a  base 
on  which  logwood  blacks,  or  other  mordant  dyes,  may  be  deposited. 

Wool  can  be  dyed  by  steeping  in  the  ferrocyanide  solution,  made 
acid  with  sulphuric  or  nitric  acid,  then  slowly  raising  the  temperature 
of  the  bath  to  boiling.  The  ferrocyanide  is  decomposed  in  part,  some 
prussic  acid  escapes,  and  the  blue  pigment  is  deposited  in  the  wool. 

TEXTILE  PRINTING 

Textile  printing  may  involve  the  application  of  a  single  coloring 
matter  to  one  side  of  the  fabric,  or  the  forming  of  intricate  designs 
in  as  many  as  18  or  20  different  colors,  by  one  passage  of  the  cloth 
through  the  printing  machine.  The  pattern  is  usually  produced  on 
one  side  only  of  the  cloth,  but  sometimes  the  same  or  a  different 
design  appears  on  each  side.  There  may  be  a  colored  figure  on  a 
white  or  colored  background,  or  a  colorless  design  may  be  produced 
on  a  colored  background. 

The  earliest  attempts  at  this  form  of  decoration,  made  by  pre- 
historic races,  were  doubtless  carried  out  by  mixing  pigments  with 
water  or  with  a  gum  solution,  and  painting  the  design  on  the  fabric. 
Later,  the  art  was  developed  to  painting  the  mordants  in  the  form  of 
the  design,  and  then  dyeing  the  fabric  in  some  natural  dyestuffs. 
Stencilling  was  invented  early,  but  great  advances  were  made  with  the 
invention  of  block  printing,  which  was  followed  by  roller  printing. 

For  block  printing  the  design  is  made  in  relief  on  blocks  of  hard 
wood.  The  cloth  is  spread  evenly  on  a  firm  table,  and  the  printer, 


TEXTILE    INDUSTRIES  547 

having  daubed  the  relief  with  color,  applies  the  block  to  the  cloth 
and  strikes  it  with  a  hammer  to  drive  the  color  into  the  fabric.  In 
order  that  the  lines  of  the  figure  may  not  overlap,  or  spaces  be  left 
unprinted  which  should  be  coloreg!,  exact  placing  or  "  registering  " 
of  the  block  is  important.  This  is  gauged  by  pin  points  set  in  the 
corners  of  the  block,  which  mark  the  exact  spot  where  it  is  to  be 
applied  for  the  next  impression.  Much  experience  is  necessary  for 
this  and  also  for  judging  of  the  amount  of  color  taken  from  the  daub- 
ing pad  by  the  block.  At  the  present  time,  block  printing  is  used  only 
for  large  designs ;  those  containing  many  colors  may  be  printed  thus, 
but  a  separate  block  is  necessary  for  each  color  used ;  and  since  one 
block  usually  serves  only  for  a  part  of  the  whole  design,  several 
blocks  may  be  needed  for  each  color.  Thus  the  process  is  slow,  labo- 
rious, and  expensive. 

Roller  or  machine  printing  has  now  generally  replaced  all  other 
processes.  One  engraved  copper  roll  is  employed  for  each  color  in 
the  design,  except  in  a  few  cases  where  a  color  is  produced  by  print- 
ing one  over  another,  as  a  yellow  over  a  blue  to  make  green.  The 
design,  drawn  by  the  artist,  is  enlarged  several  times  and  engraved 
on  a  zinc  plate.  The  copper  roll  is  turned  perfectly  true  in  a  lathe, 
and  then  polished.  Its  surface  is  coated  with  wax  or  a  special  varnish, 
through  which  the  design  is  scratched  by  a  stylus  of  a  pantagraph 
machine,  following  the  pattern  on  the  zinc  plate ;  this  reproduces  the 
design  and  at  the  same  time  reduces  it  to  the  required  size.  The  roll 
is  then  etched  with  nitric  acid,  until  the  figures  have  the  necessary 
depth.  After  washing  off  the  acid,  the  wax  is  removed,  and  the 
hollow  roll  is  slipped  on  a  mandrel  for  use  in  the  machine.  The  color 
is  fed  to  the  print  roll  from  the  color  box  by  a  revolving  cylindrical 
brush  called  the  "  furnisher,"  which  dips  into  the  color  paste.  This 
covers  the  -entire  surface  of  the  roll  with  the  color  and  fills  the  depres- 
sions of  the  design.  A  sharp  steel  blade,  called  the  "doctor,"*  rubs 
against  the  surface  of  the  roll  as  the  latter  revolves,  and  scrapes  off 
all  excess  of  color,  leaving  only  that  contained  in  the  depressions  of 
the  pattern.  Beneath  the  cloth  a  similar  blade  rubs  the  roll,  remov- 
ing from  it  any  bits  of  dirt  or  lint  which  may  adhere  after  the  cloth 
has  been  printed.  The  print  rolls  are  all  set  around  one  central  drum 
called  the  "  bowl,"  against  which  they  press,  and  which  is  covered 
with  several  thicknesses  of  strong  linen  and  woollen  cloth  called 
"  lapping,"  which  will  withstand  the  repeated  pressure  without  break- 

*  In  order  that  irregularities  may  not  be  worn  in  the  edge  of  the  doctor  or  on  the 
print  roll,  the  former  is  given  a  slight  sidewise  movement  by  a  suitable  gearing. 


548  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

ing.  This  lapping  must  be  evenly  placed,  or  streaks  will  appear 
on  the  printed  goods.  The  cloth  to  be  printed  passes  between  the 
rolls  and  the  bowl,  considerable  pressure  being  brought  to  bear  upon 
it,  so  that  it  is  forced  into  the  engraving  on  the  roll  and  takes  out  all 
the  color.  Between  the  lapping  and  the  cloth  to  be  printed,  an  end- 
less band  or  "  blanket  "  of  thick  woollen  cloth  passes.  This  adds  to 
the  elasticity  of  the  lapping,  affording  a  better  impression  of  the  en- 
graving, and  protecting  the  lapping  from  color  and  moisture.  The 
blanket  is  often  40  to  50  yards  long,  and  goes  over  drying  drums  before 
it  passes  around  the  bowl.  In  order  to  keep  the  blanket  free  from 
color  stains,  a  piece  of  unbleached  cotton  cloth,  called  "  gray  cloth  " 
or  "  back  cloth,"  is  interposed  between  it  and  the  print  cloth.  This 
gray  cloth  is  sometimes  used  once  or  twice  for  this  purpose  and  then 
sent  to  the  singeing  and  bleaching  process,  after  which  it  is  itself 
printed,  usually  with  a  dark  color.  Thus  three  long  webs  of  cloth 
pass  between  the  rolls  and  the  bowl  at  once,  —  the  blanket,  back 
cloth,  and  print  cloth. 

The  printing  colors  may  be  soluble  dyestuffs  or  insoluble  pig- 
ments made  into  a  paste  with  water,  oil,  or  other  medium ;  in  many 
cases  mordants  alone  are  printed  on  the  fabric.  It  is  also  essential  that 
the  color  pastes  shall  contain  some  material  by  which  the  pigments 
may  be  fixed  on  the  fibre  so  that  they  will  not  rub  off  in  the  finishing 
operations.  In  order  that  the  printing  colors  may  adhere  to  the  rolls 
and  not  run  when  applied  to  the  cloth,  thickening  agents  are  em- 
ployed. The  most  important  of  these  are  British  gum,  starch',  flour, 
gum  arabic,  Senegal,  or  tragacanth,  and  blood  or  egg  albumin.  It  is 
necessary  that  these  shall  not  form  any  chemical  combination  with 
the  color  or  the  mordants.  Some  thickeners  are  insoluble  in  cold 
water,  while  others  are  more  or  less  soluble,  and  the  printer  must 
select  that  best  adapted  to  his  purpose  and  the  color  he  wishes  to  use. 
The  preparation  of  color  pastes  is  called  "  color  mixing  "  and  requires 
much  care.  The  ingredients  are  mixed  in  special  vessels  called 
"  color  pans,"  these  being  jacketed  copper  kettles  which  may  be 
heated  by  steam  or  cooled  by  water,  as  required.  If  starch  or  flour 
is  used,  it  must  be  very  well  boiled  to  a  smooth  paste  before  the  color 
is  stirred  in.  British  gum  and  Senegal  are  dissolved  in  hot  water 
with  constant  stirring,  while  tragacanth  is  boiled  for  several  hours. 
Albumin  is  dissolved  in  water  at  less  than  50°  C.,  while  stirring  con- 
stantly. After  mixing,  the  color  paste  must  be  strained  to  remove 
any  lumps,  dirt,  or  grit,  and  to  form  a  smooth  paste  of  homogeneous 
character.  For  large  lots,  this  is  sometimes  done  by  machinery,  but 


TEXTILE    INDUSTRIES  549 

in  most  cases  the  straining  cloth  is  folded  over  the  paste  like  a  bag, 
and  then  twisted  by  hand  by  the  workmen,  thus  forcing  the  paste 
through  the  cloth.  It  is  now  ready  to  put  into  the  color  boxes  of  the 
machine,  from  which  the  furnisher  roll  feeds  it  to  the  print  roll. 

But  the  color  is  not  always  printed  on  the  goods.  Sometimes 
only  the  mordants,  mixed  in  the  thickener,  are  printed,  the  goods 
being  afterwards  immersed  in  the  dye-bath,  and  taking  the  color 
only  where  mordanted.  Or  a  substance  called  a  "  resist  "  is  printed 
to  prevent  the  dye  from  taking  the  fibre  in  the  printed  portions ;  thus 
white  spots  or  figures  are  left  on  a  colored  background.  Or  "  dis- 
charges "  may  be  printed  on  dyed  material,  destroying  or  bleaching 
the  color  where  they  touch. 

After  printing,  the  cloth  is  dried  by  passing  above  a  series  of 
steam  boxes,  or  hot  pipes,  but  generally  not  close  enough  to  touch 
them,  lest  some  of  the  colors  should  be  changed  by  the  heat.  With 
many  colors,  however,  the  drying  is  done  more  quickly  by  passing 
the  print  over  a  steam-heated  roll  or  "  drying-can."  For  pigments 
in  albumin  thickening,  this  direct  drying  is  sufficient  to  fix  the  color 
on  the  fibre,  and  the  goods  may  be  finished  at  once. 

The  method  of  producing  the  colored  design  in  calico  printing  is 
called  a  "  style."  The  following  are  the  more  important :  pigment 
style,  steam  style,  madder  or  dyeing  style,  oxidation  style,  discharge 
style,  and  resist  style.  The  pigment  style  is  of  less  importance 
than  it  formerly  was.  Insoluble  pigments,  such  as  ultramarine, 
Guignet's  green,  chrome  yellow,  vermilion,  etc.,  are  mixed  with  the 
thickening  paste,  printed  directly,  and  the  print  dried  by  passing 
over  a  hot  roll.  If  the  thickening  is  gum,  starch,  or  dextrine,  the 
resulting  print  is  not  fast  to  washing,  and  is  known  as  "  loose  pigment 
style."  But  if  blood  or  egg  albumin  is  used,  and  the  print  dried  at 
a  high  temperature,  or  steamed  to  coagulate  the  albumin,  the  color 
is  fixed  on  the  fibre,  and  is  fast  to  ordinary  washing  and  soaping. 

The  steam  style,  formerly  called  the  extract  style,  is  used  for 
those  colors  in  which  the  mordant,  dyestuff,  and  thickening  can  be 
mixed  cold  or  at  moderate  temperatures  without  the  formation  of 
the  color  lake.  Acetic  acid  is  often  added  to  retard  the  action 
between  the  dyes  tuff  and  mordant.  Tannic  acid  is  much  used  as  a 
mordant  in  steam  colors.  The  cloth  is  generally  prepared  by  oiling 
it  slightly  with  Turkey-red  oil,  or  "  oleine,"  before  printing.  The 
printed  cloth  is  arranged  on  racks  on  a  car  which  can  be  run  directly 
into  the  steamer,  or  the  goods  are  made  to  pass  through  a  continu- 


550  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

ous  steamer,  consisting  of  a  large  closed  vessel  containing  numerous 
rollers  at  the  top  and  bottom,  over  which  the  cloth  passes  up  and 
down  many  times.  The  steam  is  under  3  to  10  pounds  pressure, 
whereby  the  acetic  acid  vaporizes,  the  reaction  between  the  mor- 
dant and  dyestuff  is  brought  about,  and  the  color  developed  on 
the  fibre.  The  print  is  washed  in  a  soap  bath  to  remove  the 
thickening.  Steam  style  is  largely  used,  and  with  many  dyestuffs. 

When  basic  dyes  and  tannic  acid  are  used,  the  printed  and  steamed 
goods  are  passed  through  a  bath  of  tartar  emetic  or  other  antimony 
salt,  to  fix  the  color  on  the  fibre. 

In  the  madder  or  dyeing  style,  only  the  mordant  is  printed,  and 
fixed  on  the  fibre  by  drying,  steaming,  or  aging.  The  goods  are 
usually  "  dunged  "  in  a  bath  of  phosphate  or  arsenate  of  soda  (for- 
merly cow-dung  and  chalk  were  used)  to  remove  excess  of  mordant 
from  the  surface  of  the  fibre,  and  thus  prevent  its  spreading  to  the 
unprinted  portions  of  the  cloth  and  blending  the  figures.  After 
dunging,  the  goods  are  thoroughly  washed,  and  at  once  dyed  in  an 
alizarin  or  madder  bath.  With  different  mordants  these  give  differ- 
ent shades:  thus  alumina  yields  reds  and  pinks;  tin  gives  scarlet; 
chromium,  maroon ;  and,  iron,  chocolate  or  brown.  But  the  number 
of  colors  obtained  in  this  way  is  limited,  and  the  process  is  largely 
given  up  in  favor  of  the  more  convenient  steam  style. 

The  oxidation  style  is  chiefly  used  for  aniline  blacks.  The  goods 
are  printed  with  a  paste  containing  aniline  salt,  sodium  or  potassium 
chlorate,  and  usually  a  trace  of  vanadium  salt,  all  worked  into  a 
suitable  thickening.  After  printing,  the  goods  are  "  aged  "  for  two 
days,  or  for  a  short  time  in  a  steam  "  ager,"  and  are  passed  through 
a  potassium  bichromate  solution  at  70°  C. ;  they  are  then  washed  in 
a  hot  soap  solution.  Manganese  browns  for  backgrounds  are  some- 
times printed  by  padding  the  surface  of  the  cloth  with  manganous 
chloride  or  sulphate,  and,  after  drying,  padding  again  with  caustic 
soda.  The  cloth  is  then  washed  and  passed  into  a  solution  of  bleach- 
ing powder,  whereby  a  hydrated  peroxide  of  manganese  is  formed  on 
the  fibre  as  a  uniform  brown  color.  This  is  then  printed  again  by 
the  discharge  style  to  produce  a  figured  pattern. 

In  the  discharge  style,  the  dyed  cloth  is  printed  with  a  discharge 
paste,  leaving  a  white  figure  on  a  colored  ground.  Or  it  is  often  cus- 
tomary to  add  some  color  to  the  paste  which  is  not  affected  by  the 
discharge,  and  which  remains  on  the  goods  where  printed ;  e.g.  certain 
pigments,  such  as  chrome  yellow,  Guignet's  green,  and  vermilion. 
Thus  colored  figures  are  obtained  on  a  ground  of  different  color. 


TEXTILE    INDUSTRIES  551 

Common  discharges  are  stannous  chloride,  zinc  dust,  and  sodium 
bisulphite,  or  sodium  bichromate,  the  last  being  used  in  connection 
with  a  sulphuric  acid  bath.  Tartaric,  citric,  and  oxalic  acids  are 
used  as  discharges,  rendering  the  mordants  soluble  in  the  printed 
portions,  whence  they  are  removed  by  washing,  so  that,  in  subse- 
quent dyeing,  the  color  does  not  take  the  fibre  in  these  spots.  Alka- 
line discharges,  made  with  caustic  soda  and  potassium  ferricyanide, 
or  potassium  bichromate  and  caustic  soda,  are  used  with  indigo. 

In  the  resist  style,  substances  are  printed  on  the  cloth  which 
prevent  the  fixing  of  the  mordant  or  color  in  the  printed  portions. 
Thus,  when  dyed,  the  printed  pattern  appears  white  on  a  colored 
ground.  Resists  may  act  mechanically  or  chemically.  Those  of  the 
first  kind  are  generally  oils  or  resins  with  china  clay,  which  are  in- 
soluble and  prevent  access  of  the  dyestuff  to  the  fibre.  Chemical 
resists  are  generally  citrate  of  sodium,  or  acetate  of  calcium,  the  former 
being  preferred  for  preventing  the  fixing  of  alumina  or  iron  mordants, 
and  the  latter  to  hinder  the  development  of  aniline  blacks.  After 
printing,  the  cloth  is  dunged,  washed,  and  dyed.  For  resists  on  indigo- 
dyed  goods,  the  cloth  is  printed  with  zinc  sulphate  or  copper  sulphate. 

In  all  styles  where  the  cloth  is  dyed  after  printing,  the  white  parts 
of  the  figure  are  usually  discolored  by  the  dye,  and  it  becomes  neces- 
sary to  "  clear  "  them,  generally  by  "  chemicking  "  in  a  solution  of 
bleaching  powder  so  dilute  as  not  to  affect  the  color  in  the  mordanted 
parts  of  the  goods.  This  is  followed  by  a  thorough  soaping  and 
washing.  The  printed  calico  is  usually  finished  by  starching,  bluing 
slightly  to  improve  the  appearance  of  the  white,  tentering,  and  finally 
calendering  between  hot  rolls. 

Wool  is  extensively  printed  for  delaines  and  challis,  the  steam 
and  discharge  styles  being  most  commonly  employed.  It  is  usually 
prepared  for  printing  by  passing  through  bleaching  powder  liquor, 
and  then  through  an  acid  bath,  the  chlorine  imparting  to  the  wool 
a  greater  affinity  for  the  acid  colors.  The  color  is  prepared  with 
thickening,  much  as  for  cotton,  and  after  printing  the  cloth  is  usually 
steamed  and  washed.  Direct  and  basic  colors  are  printed  without 
further  addition  to  the  paste ;  acid  colors  require  a  little  oxalic  or 
tartaric  acid;  for  mordant  colors,  acetate  of  chromium  or  of  alumi- 
num is  employed,  while  for  discharge  styles  stannous  salts  are  used 
as  reducing  agents  in  the  paste. 

Silk  is  printed  in  much  the  same  way  as  wool.  It  is  usually 
mordanted  with  tin,  and  sometimes  with  an  acid. 


552  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

REFERENCES 

Dyeing  and  Calico  Printing.     F.  Crace-Calvert,  Manchester,  1876. 

Etudes  sur  les  Fibres  vegetales  textiles.     M.  Vetillard,  Paris,  1876. 

Le  Conditionnement  de  la  Soie.     Jules  Persoz,  Paris,  1878. 

Calico  Printing,  Bleaching,  and  Dyeing.     C.  O'Neill,  London,  1878. 

Bleicherei,  Farberei  und  Appretur.     C.  Romen,  Berlin,  1879. 

Die  Gewinnung  der  Gespinnstfasern.     H.  Richard,  Braunschweig,  1881. 

The  Wild  Silks  of  India.     Thomas  Wardle,  London,  1881. 

Die  Technologic  der  Gespinnstfasern.     2  Bde.     H.  Grothe,  Berlin,  1882. 

Die  Wascherei,  Bleicherei  und  Farberei  von  Wollengarnen.     R.  Sachse, 

Leipzig,  1882. 

Dyeing  and  Tissue  Printing.     W.  Crookes,  London,  1882.     (Bell  &  Sons.) 
Structure  of  the  Cotton  Fibre.     F.  Bowman,  Manchester,  1882. 
Ramie,  Rhea,  Chinagras  und  Nesselfaser.     Bouche  u.  Grothe,  Berlin,  1882. 
Traite  pratique  du  Degraissage,  etc.     A.  Gillet,  Paris,  1883. 
Ueber  pflanzliche  Faserstoffe.     F.  von  Hohnel,  Wien,  1884. 
Bleaching,  Dyeing,  and  Calico  Printing.     J.  Gardner,  London,  1884. 
The  Structure  of  Wool  Fibre.    F.  J.  Bowman.    2d  ed.    Manchester,  1885. 
Les  Soies.     N.  Rondot,  Paris,  1885. 
Report  on  Indian  Fibres  and  Fibrous  Substances.     C.  F.  Cross,  E.  J. 

Bevan,  C.  M.  King,  and  E.  Joynson,  London,  1887. 
Microscopie  der  Faserstoffe.     F.  von  Hohnel,  Wien,  1887. 
Dyeing.     A.  Sansone,  Manchester,  1888.     (Hey wood  &  Son.) 
Das  Farben  und  Bleichen  von  Baumwolle,  Wolle,   Seide,  Jute,  u.s.w. 

J.  Herzfeld,  Berlin,  1889. 
Die  Echtfarberei  der  losen  Wolle  in  ihrem  ganzen  Umfange.     Alfred 

Delmart.     3  Bde.,  1887-1891.     Rechenberg  i.  B. 

Die  Jute  und  ihre  Verarbeitung.     E.  Pfuhl.     3  Bde.     Berlin,  1888-1891. 
Handbuch  der  Farberei.     A.  Ganswindt,  Weimar,  1889. 
L' Industrie  de  la  Teinture.     C.  L.  Tassart,  Paris,   1890.     (Bailliere.) 
The  Cotton  Fibre,  Its  Structure,  etc.     Hugh  Monie,  Manchester,  1890. 
Report  on  Flax,  Hemp,  Ramie,  etc.  U.  S.  Dep't  of  Agriculture,  Washington, 

1890. 

La  Soie.     L.  Vignon,  Paris,  1890. 
Industrie  de  la  Soie.     F.  Debaitre,  Paris,  1890. 
Traite  de  Teinture  sur  laine  et  sur  etoffes  de  laine.     P.  F.  Levaux,  Liege, 

1890.     (J.  Godenne.) 
Traite  Pratique  de  Teinture  et  Impression.      M.   de  Vinant.     2d  ed. 

Paris,  1891. 

Die  chemische  Technologie  der  Gespinnstfasern.     O.  N.  Witt,  Berlin,  1891. 
Tintura  della  Seta.     Teodoro  Pascal,  Milano,  1892.     (U.  Hoepli.) 
Traite  de  la  Teinture  et  de  1'Impression.     J.  Depierre,  Paris,  1891-1892. 

2  Tomes.     (Baudry  et  Cie.) 

Die  Praxis  der  Farberei  von  Baumwolle  u.s.w.     J.  Herzfeld,  Berlin,  1892. 
Silk  Dyeing,  Printing,  and  Finishing.    J.  H.  Hurst,  London,  1892.     (Bell.) 
Textiles  Vegetaux.     E.  Lecompte,  Paris,  1893. 
La  Pratique  du  Teinturier.    Jules  Jarcon,  Paris,  1894.     2  Tomes. 
Cellulose.     Cross  &  Bevan,  London,  1895. 

Bleichen  u.  Farben  der  Seide  u.  Halbseide.     C.  H.  Steinbeck,  Berlin,  1895. 
Bleaching  and  Calico  Printing.     Geo.  Duerr  and  Wm.  Turnbull,  London, 

1896. 
The  Cotton  Plant.     Bui.  No.  33,  U.  S.  Dep't  of  Agriculture,  Washington, 

D.C.,  1896. 

Das  Anthracene  und  seine  Derivate.     G.  Auerbach.     2te  Auf.     Braun- 
schweig, 1880. 

Die  Industrie  der  Theerfarbstoffe.     C.  Haussermann,  Stuttgart,  1881. 
Die    Chemie    des    Steinkohlentheers.     G.    Schultz.     2te    Auf.     2    Bde. 

Braunschweig,  1886. 

Die  kiinstlichen  organischen  Farbstoffe.     P.  Julius,  Berlin,  1887. 
The  Chemistry  of  the  Coal-Tar  Colours.     R.  Benedikt,  translated  by 

E.  Knecht.     3d  ed.     London,  1900.     (Bell  &  Sons.) 


TEXTILE    INDUSTRIES  553 

Organische  Farbstoffe,  welche  in  der  Textilindustrie  Verwendung  finden. 

R.  Mohlau,  Dresden,  1890.     (Julius  Bloem.) 
Les  Matieres  colorantes,  etc.     C.  L.  Tassart,  Paris,  1890. 
Chemistry  of  the  Organic  Dyestuffs.     R.  Nietzki,  translated  by  Collin  & 

Richardson,  London,  1892. 
Tabellarischen     Uebersicht     der     kiinstlichen     organischen     Farbstoffe. 

A.  Lehne,  Berlin,  1894. 

Die  Chemie  der  Natiirlichen  Farbstoffe.     H.  Rupe,  Braunschweig,  1900. 
Descriptive    Catalogue   of   the   Useful    Fibre   Plants.     Dodge.     Report 

No.  9,  U.  S.  Dep't  of  Agriculture,  Washington,  D.  C.,  1897. 
Report  on  Flax  Culture.     Dodge.     Report  No.  10,  U.  S.  Dep't  of  Agri- 
culture, Washington,  D.C.,  1898. 

Die  Mercerisation  der  Baumwolle.     Gardner,  Berlin,  1898. 
Die  Kunstliche  Seide.     Carl  Silvern,  Berlin,  1900.     (Springer.) 
Die  Vegetabilischen  Faserstoffe.     Bottler,  Leipzig,  1900. 
The  Printing  of  Cotton  Fabrics.     A.  Sansone,  Manchester,  1887.     Lon- 
don, 1901. 

The  Dyeing  of  Textile  Fabrics.     J.  J.  Hummel,  London,  1902. 
Die  Animalischen  Faserstoffe.     Bottler,  Leipzig,  1902. 
The  Dyeing  of  Cotton  Fabrics.     Franklin  Beech,  London,  1901. 
The  Dyeing  of  Woollen  Fabrics.     Franklin  Beech,  London,  1902. 
Researches  on  Cellulose.     3  vols.     C.  F.  Cross  and  E.  J.  Bevan,  London, 

1901-1912. 
The  Chemical  Technology  of  Textile  Fibres.     G.  von  Georgievics,  trans. 

by  Chas.  Salter,  London,  1902. 
Taschenbuch  fur  die  Farberei  und  Farbenfabriken.     R.  Gnehm,  Berlin, 

1902. 

Textile  Fibres  of  Commerce.     Hannan,  London,  1902. 
Die  Rohstuffe  des  Pflanzenreiches.     2  vols.     J.  Wiesner,  Leipzig,  1903. 
Mercerization.     Editors  of  Dyer  and  Calico  Printer.     London,  1903. 
Tabellarische  Uebersicht  der  kiinstlichen  organischen  Farbstoffe.     Schultz 

&  Julius.     4te  Auf.     Berlin,  1903. 

Principles  of  Dyeing.     G.  S.  Fraps,  New  York,  1903.     (Macmillan  Co.) 
A  Systematic  Survey  of  the  Organic  Colouring  Matters.     Arthur  G.  Green. 

2d  ed.     London,  1904.     (Macmillan  &  Co.) 

The  Synthetic  Dyestuffs.     J.  C.  Cain  and  J.  F.  Thorpe,  London,  1905. 
Chemie  der  organischen  Farbstoffe.     R.  Nietzki.     5te  Auf.     Berlin,  1906. 
The  Textile  Fibres.     J.  Merritt  Matthews.     2d  ed.     New  York,  1907. 
Laboratory    Manual    of    Dyeing    and    Textile    Chemistry.     J.    Merritt 

Matthews,  New  York,  1909. 
Manual  of  Dyeing.     E.  Knecht,  C.  Rawson,  and  R.  Loewenthal.   2d  ed. 

3  vols.     London,  1910.     (Griffin  &  Co.) 

Chemical  Aspects  of  Silk  Manufacture.     R.  L.  Fernbach,  New  York,  1910. 
Farbenmethoden  der  Neuzeit.     Max  Bottler,  Halle,  a.  S.,  1910.     (Knapp.) 
Die  Zellulose.     C.  Piest,  Stuttgart,  1910.     (Enke.) 
Identification  of  the  Commercial  Dyestuffs.     Samuel  P.  Mulliken,  New 

York,  1910.     (Wiley  &  Sons.) 
Die  Schwefelfarbstoffe.     O.  Lange,  Leipzig,  1911. 
Tabellarische  Uebersicht  der  wichtigsten  Kupenfarbstoffe.     M.  Battegay 

u.  E.  Grandmougin.     Elssaachen  Textil-Blatt,  Gebweiler,  1911. 
The  Chemistry  of  the  Coal-tar  Dyes.     Irving  W.  Fay,  New  York,  1911. 
The  Principles  of  Bleaching  and  Finishing  Cotton.     R.   S.   Trotman, 

London,  1911. 
Bleaching  and  Dyeing  of  Vegetable  Fibrous  Material.     J.  Htibner,  New 

York,  1912. 

The  Chemistry  of  Dyeing.    J.  K.  Wood,  1913. 
Manufacture  of  Organic  Dyestuffs.    A.  Wahl,  1914. 


PAPER 

Paper  consists  of  cellulose  fibres  matted  or  felted  into  a  coherent 
sheet.  Usually  a  certain  amount  of  mineral  matter,  or  "  loading," 
is  incorporated  with  the  paper  to  increase  the  weight  and  render  it 
smooth  and  less  porous.  The  raw  materials  furnishing  the  fibre  are 
wood  pulp,  cotton  or  linen  rags,  esparto,  straw,  hemp,  flax,  jute,  etc. 
Old  paper  and  the  trimmings  and  waste  from  paper  mills  are  also  re- 
worked. The  common  loading  materials  are  clay  (kaolin),  ground 
talc  or  steatite,  gypsum,  or  precipitated  calcium  sulphate  (pearl 
hardening,  crown  filler,  etc.),  and  barium  sulphate  (blanc  fixe). 

In  nearly  every  case  the  cellulose  fibres  must  be  freed  from  in- 
crusting  matter  and  treated  in  such  a  way  as  to  reduce  the  substance 
to  a  state  of  minute  subdivision  and  to  isolate  more  or  less  com- 
pletely the  individual  fibres.  It  is  largely  in  this  isolation  that  chemi- 
cal processes  are  involved  in  the  industry. 

Wood  pulp  is  made  from  poplar  (Populus  grandidentata,  Michx.), 
spruce  (Picea  rubra,  Link.),  hemlock  (Tsuga  Canadensis,  Carr.),  pine 
(Pinus  Strobus,  L.),  cottonwood  (Populus  monilifera,  Ait.),  basswood 
(Tilia  Americana,  L.),  white  birch  (Betula  papyri/era),  and  maple 
(Acer  dasycarpum,  Ehrh.). 

Wood  pulp  is  of  two  kinds,  mechanical  and  chemical.  Mechani- 
cal pulp  is  made  by  forcing  a  large  stick  of  wood  against  a  revolving 
sandstone,  or  emery  wheel,  over  which  a  jet  of  water  plays  continu- 
ously. The  resulting  pulp  is  washed  away  by  the  water  and  passes 
several  screens  to  remove  insufficiently  disintegrated  particles.  The 
mixture  of  pulp  and  water  then  flows  into  a  tank  in  which  a  cylinder 
covered  with  wire  gauze  is  revolving.  The  water  passes  through 
and  a  layer  of  pulp  adheres  to  the  cylinder  and  is  delivered  on  to  an 
endless  blanket;  this  carries  it  to  a  pair  of  squeeze-rolls  where  it  is 
compacted.  It  is  then  cut  into  sheets  of  convenient  size,  several  of 
which  are  pressed  into  one  thick  "  board  "  for  transportation.  Me- 
chanical pulp  is  contaminated  with  lignin  and  resinous  matters, 
which  turn  brown  on  exposure  to  light.  The  fibres  are  short  and  do 
not  mat  together  well,  so  the  paper  made  from  it  is  not  strong ;  such 
pulp  is  only  used  for  cheap  paper  (e.g.  newspaper)  and  generally  in 
conjunction  with  other  fibres  and  chemical  pulp.  By  dipping  a  strip 
of  paper  into  a  solution  of  phloroglucin  in  hydrochloric  acid,  the 
presence  of  ground  pulp  may  be  detected  by  the  appearance  of  a 

554 


PAPER  555 

magenta  red  color ;  an  aqueous  solution  of  aniline  sulphate  will  yield 
a  yellow  color. 

Chemical  pulp  is  prepared  by  the  soda  process,  the  sulphite  process, 
or  by  the  sulphate  process.  The  soda  process  is  largely  used  for  soft 
woods,  especially  poplar,  cottonwood,  and  basswood.  The  bark  is  re- 
moved by  hand  shaves,  but  the  knots  and  rotten  wood  are  generally 
disregarded.  The  wood  is  put  through  a  chipping  machine  which  cuts 
it  across  the  grain  and  reduces  it  to  fragments  about  three-eighths  of 
an  inch  thick.  After  the  chips  are  dusted  by  blowing  them  against  a 
screen,  they  are  filled  into  the  digesters.  These  consist  of  upright 
steel  boilers  with  electrically  welded  joints,  and  heated  by  live  steam ; 
they  hold  3  to  4  cords  of  chips  at  one  charge.  Sometimes  rotary 
globular  boilers  holding  4  to  5  cords  are  used.  The  digester  is  nearly 
filled  with  chips,  which  are  then  covered  with  a  caustic  soda 
liquor  of  about  11°  Be.  They  are  boiled  for  from  8  to  10  hours  at  a 
pressure  of  from  90  to  120  pounds.  The  effect  of  this  "  cooking  "  is 
to  reduce  the  wood  to  a  soft  mass  of  grayish  brown  color,  while  the 
liquor  has  become  dark  brown  and  has  a  density  of  llj°  Be.  The 
non-cellulose  matters  of  the  wood  (lignin,  resins,  etc.),  which  consist 
largely  of  organic  acids,  are  decomposed  by  or  combine  with  the  soda, 
and  consequently  the  alkali  is  nearly  all  neutralized  during  the  pro- 
cess. The  pulp  and  "  black  liquor  "  are  blown  out  into  a  tank  having 
a  sloping  bottom  and  covered  with  a  closely  fitting  lid.  Here  the 
pulp  is  systematically  washed  and  the  wash-waters  are  saved  until 
their  average  density  falls  below  8°  or  9°  Be.  The  liquor  is  pumped 
into  a  multiple-effect  evaporator  and  concentrated  to  38°  Be.,  when  it  is 
sent  directly  to  a  revolving  calcination  furnace  (p.  4)  from  which  a  dry 
soda-ash  is  recovered;  this  is  recausticized  for  use  in  the  digesters. 
From  85  to  90  per  cent  of  the  original  soda  is  thus  recovered. 

The  caustic  soda  has  a  direct  action  on  the  .cellulose,  especially 
when  the  pressure  is  high ;  hence  some  of  the  fibre  is  dissolved  or 
destroyed,  while  all  of  it  is  weakened  somewhat.  The  pulp  produced 
is  soft,  and  though  of  a  dark  color,  is  easily  bleached  in  the  case  of 
poplar.  The  yield  from  this  wood  is  about  40  per  cent  of  its  weight. 

In  the  sulphite  process,  the  wood  (generally  coniferous  wood)  is 
boiled  under  pressure  with  sulphurous  acid  or,  more  commonly,  with 
acid  sulphite  of  calcium  and  magnesium.  The  action  of  the  sulphur- 
ous acid  under  pressure  and  at  a  high  temperature  upon  the  lignin 
and  other  incrusting  matters  of  the  wood  fibre  is  probably  a  hydroly- 
sis ;  by  this,  these  complex  molecules  are  broken  down,  the  resulting 
products  being  largely  organic  acids  and  aldehydes,  soluble  in  the 


556  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

liquor.  But,  owing  to  secondary  reactions  among  themselves,  cer- 
tain acids  and  insoluble  tar-like  substances  are  also  formed,  which 
the  reducing  nature  of  the  sulphurous  acid  does  not  appear  to  entirely 
prevent.  The  acid  sulphites  react  much  like  sulphurous  acid,  but 
the  bisulphites  combine  with  the  aldehydes  formed  in  the  first  stage 
of  the  decomposition,  producing  stable  and  soluble  double  salts.  The 
organic  acids  which  are  also  formed  decompose  the  bisulphites  and 
form  soluble  calcium  and  magnesium  salts,  while  sulphurous  acid  gas 
is  set  free,  causing  a  constant  increase  in  the  pressure  within  the  diges- 
ter. The  acid  sulphites  also  tend  to  bleach  the  coloring  matter  of  the 
fibres  by  forming  colorless  compounds  with  them,  but  this  is  a  very 
unstable  bleach  and  the  original  color  soon  returns  when  the  pulp  is 
made  into  paper.  Hence  for  permanent  whiteness  the  pulp  is  further 
bleached  with  chlorine.  Bisulphite  of  calcium  is  unstable  and  de- 
composes readily  into  neutral  sulphite,  setting  free  sulphurous  acid. 
This  results  in  the  precipitation  of  the  neutral  sulphite  on  the  fibre, 
which  is  left  harsh,  even  after  long  washing.  Magnesium  bisulphite 
is  more  stable,  and,  although  less  corrosive  to  the  fibre,  it  dissolves  the 
non-cellulose  matter  even  more  completely  than  does  the  lime  salt ; 
further,  any  sulphate  or  neutral  sulphite  which  may  be  formed  is 
easily  washed  off. and  the  pulp  is  left  soft  and  white.  Sodium  bisul- 
phite gives  a  better  product  than  either  of  the  above,  and  strong 
liquors  can  be  made  from  it ;  but  it  is  too  expensive  for  general  use. 

Bisulphite  liquors  are  made  by  passing  sulphur  dioxide  through 
towers  packed  with  dolomite,  over  which  water  is  trickling;  or  by 
leading  sulphur  dioxide  into  closed  vessels  about  half  full  of  milk  of 
lime  (prepared  from  dolomite).  Within  the  vessel  is  a  system  of  re- 
volving paddles,  half  submerged  in  the  liquor,  and  thus  presenting 
large  surfaces,  wet  with  the  liquor,  to  the  action  of  the  gas;  they 
also  splash  the  spray  into  the  atmosphere  of  gas,  thus  securing  rapid 
and  complete  absorption.  Usually  a  series  of  three  of  these  tanks 
is  used,  the  strong  gas  entering  the  most  concentrated  liquor,  which 
is  thus  brought  up  to  a  gravity  of  about  1.045  to  1.060  (6°  to  8°  Be.), 
and  containing  3J  to  4j  per  cent  SC>2.  The  sulphur  dioxide  is  pre- 
pared by  burning  brimstone  in  an  iron  retort.  Much  care  is  neces- 
sary in  regulating  the  air  supply  to  the  burner ;  too  much  air  forms 
SOa,  which  produces  sulphates  in  the  liquor;  it  also  causes  over- 
heating of  the  furnace,  and  consequent  sublimation  of  sulphur  into 
the  cooling  pipes  and  absorption  tanks,  where  polythionic  acids  (thio- 
sulphates)  are  formed.  These  precipitate  sulphur  in  the  pulp  in  the 
digester,  and  cause  trouble  in  the  paper  making.  TOO  little  air  sup- 


PAPER  557 

plied  to  the  burner  also  causes  sublimation  of  sulphur.  The  hot  gases 
from  the  burner  are  cooled  to  10°  or  15°  C.,  by  passing  through  water- 
cooled  lead  pipes.  For  the  strongest  liquor,  the  temperature  in  the 
absorption  tanks  must  be  kept  as  low  as  possible.  The  tanks  for 
storing  the  sulphite  liquors  are  sometimes  lined  with  lead,  though 
unlined  tanks  of  hard  pine  are  often  used.  Large  quantities  of  liquor 
may  be  kept  without  much  loss  of  strength,  either  through  oxidation, 
or  evolution  of  gas.  Bronze  rotary  pumps  or  lead-lined  acid-eggs  are 
used  for  pumping  the  liquor. 

Sulphite  digesters  are  usually  made  of  steel,  lined  with  lead,  and, 
inside  of  this,  a  layer  of  hard-burned,  acid-resisting  brick  laid  in 
Portland  cement.  Numerous  half -inch  holes  in  the  steel  plates  allow 
the  escape  of  steam  or  gas  from  behind  the  lining  in  case  of  a  leak, 
thus  preventing  warping  of  the  lead  when  the  digester  is  blown  off. 
Sometimes  the  lead  lining  is  omitted  and  the  brick  laid  in  a  litharge- 
glycerine  cement,  directly  against  the  steel.  The  acid  liquors  have  a 
very  corrosive  action  on  iron,  and  much  experimenting  has  been  done 
to  find  a  suitable  lining.  Lead  resists  the  action  very  well,  but  when 
used  alone  as  a  lining  it  soon  cracks  or  warps,  and  also  gives  trouble 
through  its  tendency  to  "  crawl."  By  filling  the  digester  entirely  full 
of  liquor  and  heating,  a  layer  of  calcium  sulphite  may  be  deposited 
as  scale  on  the  walls,  and  affords  much  protection.  Bronze  digesters 
have  been  tried,  but  are  expensive,  do  not  resist  the  liquor,  and  are 
lacking  in  strength,  several  having  exploded.  Digesters  are  built 
upright  or  horizontal,  and  less  frequently  of  globular  form,  the  latter 
intended  to  rotate,  the  steam  being  admitted  through  the  trunnions. 
Large  digesters  hold  12  to  14  cords  of  chips  at  one  filling ;  they  are 
provided  with  blow-off  valves  for  the  escape  of  gas  during  the  cooking. 

For  making  sulphite  pulp,  all  bark,  knots,  and  dead  wood  are  cut 
out  of  the  sticks,  which  are  then  chipped  across  the  grain,  as  for 
soda  pulp.  The  boiling  is  carried  on  by  the  "  quick-cook  "  or  the 
"  slow-cook  "  method.  In  the  quick-cook  system  the  digester  is  com- 
pletely filled  with  chips,  and  all  the  liquor  (about  1200  gallons  per 
cord  of  chips)  is  run  in  as  rapidly  as  possible,  through  a  large  pipe. 
As  a  rule  the  liquor  is  about  10°  Tw.  (7°  Be.),  with  3|  per  cent  SO2. 
The  pressure  is  raised  slowly,  in  order  to  avoid  the  hammer  effect 
of  the  live  steam  coming  in  contact  with  the  cold  digester  content, 
and  also  to  avoid  too  high  a  temperature  before  the  liquor  has  pene- 
trated into  the  interior  of  the  chips;  otherwise  the  wood  may  be 
burned,  and  rendered  brown  or  red.  The  temperature  (which  is  the 
most  important  factor  in  the  process)  should  not  exceed  300°  to  312° 


558  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

F.  (149°  to  156°  C.).  It  should  be  regulated  by  a  thermometer,  since 
no  dependence  can  be  placed  on  the  pressure  indications  as  a  means 
of  determining  the  conditions  within  the  digester.  During  the  8  or  10 
hours'  boiling,  considerable  gas  is  evolved,  and  there  is  a  steady  in- 
crease in  the  pressure,  which  reaches  75  to  85  pounds. 

In  the  slow-cook  process  a  large  digester  (14  by  45  feet),  heated 
by  lead  coils  in  the  lower  part,  is  used.  The  chips  are  packed  evenly 
in  the  digester,  arid  wet  steam  at  100°  C.  is  introduced  for  12  hours, 
until  all  the  air  is  expelled  and  the  charge  heated  to  100°  C.  No 
pressure  is  used,  and  the  condensed  water  is  allowed  to  flow  out 
freely.  Then  the  manhole  and  outlet  cocks  are  closed,  and  the  cold 
liquor  of  1.042  sp.  gr.  is  run  in.  This  causes  a  partial  vacuum,  and  a 
better  penetration  of  the  liquor  into  the  chips  is  secured.  When  the 
digester  is  almost  full  of  liquor,  the  heating  is  begun,  and  raised  to 
110°  as  rapidly  as  possible,  though  it  usually  requires  12  hours.  The 
steam  is  so  regulated  that  this  temperature  is  maintained  for  about  12 
hours,  when  it  is  slowly  raised  to  120°  C.,  and  a  maximum  pressure 
of  about  50  pounds  is  secured.  The  total  time  of  boiling  is  about  36 
hours.  Usually  the  pulp  is  blown  out  of  the  digester  into  a  draining 
tank,  where  it  is  washed  with  pure  water.  When  washed  in  the 
digester,  as  is  sometimes  done,  cold  water  must  be  run  in  at  once  after 
the  liquor  is  drawn  off,  to  prevent  burning  the  pulp  by  the  heat  radiated 
from  the  digester  walls.  Pulp  which  is  to  be  bleached  must  be 
thoroughly  washed,  since  any  bisulphite  left  in  the  fibre  acts  as  an 
"  antichlor,"  and  destroys  the  bleach  liquor.  The  undecomposed 
shives  must  be  removed  by  screening  the  pulp  before  bleaching. 

Sulphite  pulp  has  longer  and  stronger  fibre  than  soda  pulp,  and 
is  ligher  colored,  some  samples  being  nearly  as  white  as  the  bleached 
pulp.  It  is  often  used  unbleached,  but  contains  some  dirt  and  has  a 
harsh  feel.  If  the  chips  have  not  been  entirely  covered  by  the  liquor, 
or  if  the  latter  has  been  weakened  by  too  much  gas  blown  off  during 
the  boiling,  the  pulp  may  be  burned,  and  black,  charcoal-like  specks 
appear  in  it.  The  waste  sulphite  liquors  are  light  brown  color,  and 
contain  much  extractive  matter  from  the  wood ;  their  disposal  is  often 
a  serious  matter,  and  it  has  been  suggested  *  that  they  may  furnish 
material  for  oxalic  or  pyroligneous  acid,  or  alcohol. 

In  the  sulphate  process,  the  lignin  and  other  non-cellulose  matter 

of  coniferous  woods  are  dissolved  in  hot  solutions  of  alkali  sulphides, 

leaving  a  fibre  of  unusual  strength.     The  sodium  sulphide  employed  is 

made  by  the  reduction  of  sodium  sulphate  (salt-cake).     The  sulphide 

*  Griffin  and  Little,  Chemistry  of  Paper  Making,  p.  271. 


PAPER  559 

is  largely  recovered  by  evaporation  and  incineration  of  the  "  black 
liquors  "  from  washing  the  pulp ;  the  organic  matter  in  the  liquor  is 
more  than  sufficient  to  reduce  the  sulphate  added  to  make  up  the 
sulphide  loss.  The  chipped  wood  (spruce,  fir,  pine,  etc.)  is  cooked 
from  four  to  seven  hours  at  100  Ibs.  pressure  (about  160°  C.)  in  a  solu- 
tion containing  sodium  hydroxide,  sulphide,  sulphate,  and  carbonate ; 
of  these  only  the  first  two  are  active  in  disintegrating  the  wood. 
Approximately  six  equivalents  of  hydroxide  to  four  of  sulphide  are 
used ;  high  sulphide  with  less  alkali  and  longer  cooking  yields  better 
and  stronger  pulp.  The  time  of  cooking  is  influenced  by  the  tempera- 
ture, pressure,  concentration  of  the  liquor,  and  amount  of  moisture  in 
the  wood.  After  cooking,  the  stock  is  blown  into  drainers  and  then 
washed  by  counter-current  flow ;  the  strongest  wash-water,  or  black 
liquor,  is  returned  to  the  digester  room  and  used  to  dilute  the  solution 
for  the  next  cook ;  the  intermediate  wash-water  (about  10°  Be.)  passes 
to  the  concentration  and  recovery  system ;  the  very  dilute  washings 
serve  as  first  wash-liquor  on  the  next  batch  of  pulp.  The  concentra- 
tion of  the  intermediate  wash-liquor  is  done  in  multiple  effects  to  25° 
Be. ;  then  in  a  Porion  surface  heated  evaporator  (p.  4)  to  35°  Be. ;  the 
thick  liquor  now  passes  through  a  25-foot  rotary  furnace,  where  it  is  re- 
duced to  a  pasty  mass,  which  flows  into  a  calcining  furnace  (about  10 
feet  diameter  by  15  feet  high)  lined  with  magnesia  brick  and  in  which 
salt-cake,  to  make  up  the  loss,  is  added.  The  charge,  as  a  burning 
semi-fluid  mass,  lies  in  the  bottom  of  the  furnace,  and  wood  is  charged 
on  top  as  fuel.  A  large  excess  of  air  is  blown  in  at  the  bottom  to 
secure  rapid  combustion,  and  the  melt  is  drawn  off  into  a  tank  of 
water ;  after  solution,  the  carbonate  is  causticized  with  lime,  and  the 
settled  liquor,  containing  about  5  Ibs.  of  available  Na2O  per  cubic 
foot,  is  sent  to  the  digester  room  and  diluted  with  black  liquor  before 
use.  The  combustion  gases  from  the  calciner  pass  to  the  rotary  fur- 
nace and  Porion  evaporator,  which  they  heat  by  counter-current  flow. 
About  400  Ibs.  of  available  Na2O  per  ton  of  chips  are  required,  and  each 
digester  yields  about  6|  tons  of  finished  pulp  (10  per  cent  moisture). 
The  pulp  is  difficult  to  bleach  and  finds  use  mainly  for  tough  and  strong 
wrapping  paper  (Kraft  paper).  Much  sulphur  dioxide  is  lost  in  the 
furnace  gases,  which  lowers  the  sulphide  content  of  the  liquor 
materially. 

The  pulp  made  by  any  of  the  above  processes  is  sent  to  the 
"  Hollander,"  or  "  beating  engine  "  (Fig.  121).  This  is  an  oval  tub 
15  to  20  feet  long  by  3j  feet  deep,  and  having  a  vertical  partition 
called  the  "  mid-feather  "  extending  along  the  middle,  about  two- 


560 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


FIG.  121. 


thirds  of  its  length.  On  one  side  of  this  and  extending  across  one- 
half  of  the  width  of  the  tub  is  a  large  roll  (A),  carrying  on  its  circum- 
ference a  number  of  knives  (C).  The  floor  is  curved  upward  behind 

the  roll  (A),  conforming 
closely  with  its  curvature, 
but  extending  only  about 
half  its  height,  as  shown 
at(B).  From  this  highest 
point  the  floor  falls  away 
to  the  level  of  the  rest  of 
the  tub  bottom.  Under 
the  roll  is  the  "bed-plate" 
(D),  fitted  with  knives 
similar  to  those  on  (A). 
(A)  is  revolved  in  the 
direction  shown  by  the 
arrow,  and  the  pulp  is 
drawn  in  between  the  roll  (A)  and  the  curved  bottom  (D),  and 
the  fibres  are  torn  apart.  It  then  passes  over  the  back-fall  (B) 
and  thence  around  through  the  passage  on  the  other  side  of  the  mid- 
leather  to  the  front  of  the  roll  and  again  passes  between  the  knives. 
(A)  is  suspended  upon  adjustable  bearings  so  that  the  distance  between 
the  two  sets  of  knives  may  be  regulated.  They  are  not  set  very  close 
for  breaking  and  disintegrating  the  washed  pulp,  as  it  is  not  desired 
to  break  the  knots  and  undecomposed  wood,  which  would  cause  dirt 
and  shive  in  the  pulp. 

In  order  to  complete  the  washing  of  the  pulp  during  its  disin- 
tegration one  or  two  drum-washers  (E)  are  usually  placed  in  each  hoi- 
lander.  These  are  rotating  cylinders  covered  with  fine  wire  gauze 
and  divided  into  compartments  by  curved  partitions.  A  conical  tube 
passes  through  the  centre  of  the  drum,  the  narrow  end  being  towards 
the  mid-feather.  The  partitions  radiate  from  this  cone  to  the  wire 
gauze  periphery  of  the  drum.  The  outer  end  of  the  drum  is  solid, 
but  that  next  the  mid-feather  has  a  central  opening  (F),  through 
which  each  compartment  discharges  its  content  of  water  into  the 
trough  attached  to  the  mid-feather.  The  drum,  supported  in  adjust- 
able bearings,  is  partly  submerged,  and  the  water,  passing  through  the 
gauze,  is  caught  in  the  compartments  as  the  drum  rotates  and  dis- 
charged through  (F).  It  flows  into  the  trough  and  out  through  the 
pipe  (G).  The  gauze  holds  back  the  pulp,  which  again  passes  around 
the  mid-feather  to  the  roll  (A). 


PAPER 


561 


A  form  of  Hollander,  requiring  less  floor  space,  is  shown  in  Fig. 
122.  In  this  the  pulp  passes  below  the  floor  and  back-fall  on  its 
return  to  the  front  of  the  roll.  The  machine  is  but  little  wider  than 
the  length  of  the  roll  (A),  the  washing  drum  (E)  being  directly  behind 
the  roll. 

After  breaking,  the  pulp  is  carried  by  a  strong  stream  of  water 
on  to  a  sluice  or  inclined  way  having  a  number  of  transverse  slats 
across  the  bottom.  The  knots  and  lumps  lodge  against  these  obstruc- 
tions, while  the  fine  pulp  flows  on  with  the  water  to  the  bleaching 
tanks. 

Rags,  both  cotton  and  linen,  are  largely  used  in  paper  making. 
These  are  collected  in  all  countries,  and  arrive  at  the  mill  in  vari- 
ous conditions  of  filth.  They  are  sorted  by  hand,  the  seams  cut 


FIG.  122. 

open,  and  all  buttons,  metallic  hooks,  etc.,  removed.  The  dust  is 
beaten  out  in  machines  having  rapidly  revolving  arms,  and  then 
the  rags  are  cut  into  small  pieces  and  boiled  for  12  hours  or  longer, 
under  the  pressure  of  60  or  70  pounds,  in  rotary  horizontal  cylinders, 
or  in  horizontal  kiers  (p.  504),  with  5  to  18  per  cent  of  milk  of  lime. 
Sometimes  a  little  soda-ash  is  added  to  the  liquor  for  colored  rags. 
After  boiling,  they  are  dumped  in  heaps  to  drain  and  soften  for  a  day 
or  two.  After  washing  with  hot  water,  they  are  sent  to  the  pulping 
machine. 

Esparto,  or  Spanish  grass,  is  derived  from  Lygeum  Spartum,  Loefl, 
and  Stipa  tenacissima,  L.  The  bast  fibres  are  similar  to  those  of 
straw,  but  give  a  stronger  paper.  It  is  chiefly  used  in  Europe,  being 
too  expensive  to  compete  with  wood  pulp  in  this  country.  Esparto 
and  straw  are  boiled  with  caustic  soda  in  upright  digesters.  In  rotary 
boilers  the  fibre  forms  little  balls  ("  fish  eggs  "),  which  cause  little 
2o 


562  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

spots  or  lumps  in  the  paper.  The  pressure  and  time  of  boiling  vary. 
The  waste  liquor  is  evaporated,  and  the  alkali  recovered  (p.  555). 
After  washing,  the  pulp  bleaches  well  with  bleaching  liquor.  In  this 
country,  straw  is  generally  boiled  with  lime  to  prepare  a  pulp  for 
strawboard. 

Jute  has  very  short  fibre,  so  the  fibre  bundles  are  not  separated, 
and  only  the  lime-boil  is  employed. 

The  bleaching  of  paper  pulp  is  done  by  agitation  with  a  weak  cal- 
cium hypochlorite  solution.  If  the  liquor  is  heated  to  90°  or  100°  F., 
or  a  little  acid  added,  the  process  is  hastened.  Alum  forms  aluminum 
hypochlorite  with  bleaching  powder  solutions,  which  is  very  effective ; 
a  slightly  acid  alum  or  "  bleaching  "  alum  is  commonly  used.  The 
bleaching  is  carried  on  in  special  vessels  ("  chests  "),  or  in  the  beating 
engines  or  hollanders,  the  latter  giving  the  best  results.  Only  a  clear 
solution  of  bleaching  powder  should  be  used,  so  that  no  dirt  be  intro- 
duced, as  it  would  cause  spots  in  the  paper.  Rags  require  the  least 
bleaching  (2  to  5  pounds  bleaching  powder  to  100  pounds  of  stock), 
and  spruce  pulp  the  most  (about  18  to  25  pounds  per  100  pounds  for 
sulphite  spruce  pulp).  As  soon  as  bleached,  the  process  should  be 
stopped,  especially  if  the  liquor  has  been  heated ;  otherwise  the  fibre 
is  liable  to  be  chlorinated,  and  color  again  taken  up.  The  excess  of 
hypochlorite  in  the  pulp  is  washed  out  with  water,  or  is  destroyed  by 
adding  an  antichlor,  such  as  sodium  thiosulphate  (p.  61),  in  the  beat- 
ing engine.  Neutral  calcium  sulphite  is  also  recommended,  but  its 
action  is  slow  :  — 

Ca(C10)2  -1-  2  CaSO3  =  2  CaSO4  +  2  CaCl2. 

The  pulp  must  be  thoroughly  washed  after  bleaching,  even  when 
antichlors  are  used,  since  injurious  substances  may  be  left  in  the  pulp. 
The  action  of  the  antichlor  is  as  follows  :  — 

2  Ca(C10)2  +  Na2S2O3  +  H2O  =  2  NaCl  +  2  CaSO4  +  2  HC1 ; 
or,  in  dilute  solutions  :  — 
Ca(ClO)2  +  4  Na2S2O3  +  H2O  =  2  Na2S4O6  +  2  NaOH  +  CaO  +  2  NaCl. 

Materials  such  as  ozone,  hydrogen  peroxide,  sulphurous  acid,  or 
liquid  chlorine,  have  been  suggested  for  bleaching,  but  these  are  of 
much  less  importance  than  the  hypochlorites. 

The  paper-making  process  is  chiefly  mechanical.  It  is  essential 
that  the  water  used  be  clear  and  colorless,  since  color  or  suspended 


PAPER  563 

matter  will  he  taken  up  l>y  the  pulp.  The  first  operation  is  "  fur- 
nishing "  or  charging  the  hollander  with  the  stock ;  the  kinds  and 
quantity  of  material  employed  depend  on  the  quality  of  the  paper  to 
be  produced.  Rag  stock  is  only  used  for  the  best  grades,  especially 
writing  papers.  New  linen  rags  and  waste  are  used  for  bond  paper, 
but  the  softer  writing  papers  are  made  from  old  rags.  The  quality 
of  paper  depends  largely  on  the  thorough  separation  of  the  fibres  and 
mixing  of  the  ingredients  in  the  hollander.  In  order  to  give  the  paper 
body,  weight,  and  smoothness,  mineral  filler  or  "  loading  "  material 
is  employed.  This  must  be  exceedingly  fine,  and  not  have  too  high 
a  specific  gravity  or  solubility  in  water,  as  its  retention  in  the  mat 
of  the  fibre  would  be  thus  reduced.  It  must  be  free  from  dirt,  grit, 
and  mica,  since  these  cause  scratches  on  the  polishing  rolls  or  spots' 
on  the  paper.  The  loading  is  done  in  the  hollander  after  the  fibre 
has  been  well  beaten  with  water.  The  filler  is  mixed  with  the  pulp, 
and  then,  for  engine-sized  paper,  the  sizing  materials  are  added,  and 
the  whole  beaten  until  a  perfect  mixture  of  the  materials  is  obtained. 
Papers  intended  for  printing  or  writing  must  be  sized  or  coated 
on  the  surface  with  some  substance  which  will  prevent  the  absorp- 
tion and  consequent  spreading  of  the  ink.  For  liquid  writing  inks,  the 
sizing  must  be  more  perfect  than  for  the  viscid  printing  inks.  Almost 
the  only  sizing  materials  now  used  are  gelatine,  "  animal  size  "  (used 
on  the  better  grades  of  paper),  rosin,  and  casein.  These  are  applied 
in  several  ways.  Animal  size  is  applied  to  hand-made  papers  by 
dipping  each  sheet  separately  into  a  tub  of  the  glue  solution,  and 
allowing  it  to  dry  slowly.  The  operation  is  called  "  tub  sizing.'* 
Machine-made  writing  paper  is  passed  in  continuous  web  through  a 
trough  filled  with  the  glue  solution.  It  is  then  cut  into  sheets,  and 
dried  very  slowly  by  hanging  it  in  a  loft  kept  at  an  even  temperature ; 
or,  in  cheaper  grades,  after  leaving  the  size  trough,  the  web  passes 
over  a  series  of  skeleton  driers,  within  which  fans  keep  up  a  rapid 
circulation  of  air.  Slow  drying  is  essential  to  animal  size,  in  order  to 
bring  it  to  the  surface.  Printing  papers  (except  some  kinds  of  news- 
paper) are  "  engine-sized  " ;  i.e.  a,  rosin  soap  (prepared  by  boiling 
rosin  with  soda-ash)  is  added  in  the  hollander,  and,  after  beating,  a 
solution  of  aluminum  sulphate  is  introduced.  The  alum  decomposes 
the  rosin  soap,  forming  a  precipitate  of  free  rosin,  and  perhaps  some 
alumina,  which  become  entangled  between  the  fibres.  When  the 
paper  passes  between  the  hot  calender  rolls  in  finishing,  this  rosin 
fuses  and  forms  a  varnish-like  layer  on  the  surface.  The  aluminum 
sulphate  should  be  neutral  or  basic,  since  free  acid  decomposes  the 


564  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

size  and  injures  the  color  and  strength  of  the  paper.  An  excess  of 
alum  over  the  amount  needed  to  decompose  the  rosin  soap  must  be 
used ;  and  the  precipitated  alumina  helps  to  hold  the  finer  parts  of 
the  fibre  and  filler  in  the  pulp  while  forming  the  sheet. 

Paper  is  usually  colored  by  adding  pigments  or  dyes  to  the  pulp 
in  the  hollander.  For  white  paper,  the  slight  yellow  tinge  of  bleached 
fibre  is  neutralized  with  a  trace  of  blue  or  pink,  ultramarine  or  coal- 
tar  dyes  being  used.  Some  pigments  are  precipitated  on  the  fibre 
by  adding  solutions  in  the  hollander ;  e.g.  potassium  bichromate  and 
lead  acetate. 

The  sheet  is  formed  in  three  different  ways :  by  the  hand  frame, 
by  the  cylinder  machine,  and  by  the  Fourdrinier  machine.  The  hand 
frame,  used  for  hand-made  paper,  is  simply  a  rectangular  frame, 
covered  with  wire  gauze,  and  having  a  slight,  removable  ledge  around 
the  sides.  This  frame  is  submerged  in  the  pulp,  mixed  to  a  thin 
cream  with  water ;  when  raised,  the  ledge  retains  some  of  the  pulp  on 
the  gauze,  while  the  water  drains  through;  at  the  same  time  the 
workman  shakes  the  frame  slightly  from  side  to  side,  causing  the  fibres 
to  "  felt,"  and  forming  a  mat  of  pulp  on  the  gauze.  The  frame  is  then 
inverted  over  a  woollen  felt  blanket,  on  which  the  sheet  of  pulp  drops. 
A  number  of  these  pieces  of  felt,  each  carrying  a  sheet  of  pulp,  are 
piled  one  above  the  other,  and  heavily  pressed  until  the  water  is  ex- 
pelled. The  sheets  are  then  "  tub-sized,"  as  above  described.  The 
final  finish  is  given  by  calendering  between  hot  rolls. 

The  cylinder  machine  is  essentially  the  same  as  that  described  for 
mechanical  pulp,  on  p.  554.  The  web  of  paper  pulp  is  carried  on  an 
endless  blanket  over  a  large  drying  cylinder,  and  then  lifted  and  passed 
between  heated  rolls.  The  paper  thus  made  is  weak,  since  the  fibres 
are  not  well  felted.  They  are  used  for  tissue  and  blotting  papers, 
and  are  not  sized. 

The  Fourdrinier  machine  is  very  complicated.  Essentially,  it  is 
as  follows:  An  endless  web  of  wire  gauze  is  supported  horizon- 
tally on  a  number  of  rollers,  and  travels  continually,  in  one  direction. 
The  paper  pulp  flows  on  to  this  from  a  storage  tank  called  the  "  stuff 
chest,"  the  thickness  of  the  sheet  being  regulated  by  the  supply  of 
pulp.  The  wire  gauze  is  given  a  continuous  sidewise  shaking  motion 
which  felts  the  pulp,  while  the  water  drains  away.  The  water  is 
drawn  away  by  the  action  of  "  suction  boxes  "  from  which  the  air 
can  be  partially  exhausted,  and  over  which  the  gauze  travels.  The 
web  is  next  transferred  to  an  endless  blanket  which  carries  it  between 
squeeze-rolls,  and  then  on  to  a  second  felt,  where  it  is  again  passed 


PAPER  565 

between  rolls.  It  finally  passes  a  series  of  "  couch  rolls/'  "  press 
rolls,"  drying  cylinders,  and  calender  rolls  to  compact,  dry,  and  polish 
the  paper. 

By  fixing  a  slightly  raised  design  on  the  wire  gauze  of  the  hand 
frame  the  paper  is  made  slightly  thinner  along  the  lines  of  the  pattern, 
and  so-called  "  water  marks  "  are  made.  The  same  effect  is  obtained 
on  paper  made  on  the  Fourdrinier  machine  by  placing  a  light  roller 
("  dandy  roll  ")  carrying  the  design  in  relief,  between  the  first  and 
second  suction  boxes,  so  that  an  impression  is  made  on  the  soft  pulp. 
If  the  roll  is  covered  with  wire  gauze,  the  impression  of  the  weave  of 
the  gauze  is  obtained,  producing  the  "  wove  "  papers.  A  smooth  roll 
carrying  ridges  forms  the  parallel  lines  on  "  laid  "  paper.  By  using 
a  roll  with  a  depressed  or  engraved  design  the  paper  is  made  thicker 
in  the  lines  of  the  pattern.  Imitation  water  marks  are  often  made 
by  pressing  the  finished  paper  with  plates  carrying  the  design  in  re- 
lief, or  by  slightly  parchmentizing  the  surface  by  printing  with  cer- 
tain chemicals,  such  as  zinc  chloride  or  sulphuric  acid. 

The  finishing  of  smooth  and  highly  sized  paper  is  done  by  calen- 
dering, or  passing  the  web  between  polished  rolls  of  chilled  iron, 
under  heavy  pressure.  A  higher  gloss  is  obtained  by  using  calenders 
with  rolls  made  of  heavily  pressed  paper,  alternating  with  polished 
iron  rolls.  Friction  calendering  consists  in  passing  the  paper  between 
a  pressed  paper  roll  running  at  high  speed,  and  an  iron  roll  running 
slowly.  For  very  high  gloss  the  paper  is  "  plated  " ;  i.e.  passed 
through  heavy  rolls  while  the  sheets  lie  between  polished  zinc  plates. 

Printing  papers  are  usually  white,  and  often  contain  a  large  amount 
of  loading  material.  In  this  country  they  are  chiefly  made  from 
wood  pulp.  Some  kinds  are  heavily  calendered  to  secure  a  smooth 
surface.  Cheap  newspaper  is  largely  made  of  mechanical  pulp. 

Wrapping  papers  are  made  from  straw,  jute,  manila  hemp,  old 
rope,  and  colored  rags.  The  stock  is  seldom  bleached,  and  hence  is 
very  often  deeply  colored.  Wrapping  papers  are  frequently  calendered 
and  always  sized. 

Writing  papers  are  made  from  the  best  materials,  and  are  highly 
sized  and  carefully  calendered. 

Blotting  and  tissue  papers  are  unsized  and  unfilled,  the  former 
being  loosely  felted  and  thick;  the  latter  is  made  from  long  fibres, 
especially  hemp  and  cotton,  and  is  the  thinnest  paper  made. 

Parchment  paper  is  made  by  dipping  unsized  paper  into  sulphuric 
acid,  diluted  with  one-fourth  its  volume  of  water,  to  which  a  little 
glycerine  is  added.  It  is  quickly  removed  and  washed  with  water, 


566  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

then  with  dilute  ammonia,  and  again  with  water.  The  acid  converts 
the  exterior  cellulose  of  the  fibres  into  amyloid,  which  coats  the  fibres 
and  cements  them  together,  forming  a  translucent  parchment-like 
material  of  great  toughness.  The  action  of  strong  zinc  chloride  solu- 
tion (sp.  gr.  1.82)  is  also  to  parchmentize  the  paper.  After  washing, 
the  paper  is  pressed  between  rolls,  dried,  and  calendered. 

By  long-continued  beating  of  pulp  or  rags,  in  the  hollander,  until 
all  fibre  structure  is  broken  down,  a  gelatinous  mass  is  produced, 
which,  when  run  upon  a  paper  machine,  gives  a  thin,  transparent 
film,  resembling  ordinary  parchment  paper.  This  is  much  used  for 
wrapping  confectionery,  butter,  and  for  other  purposes  when  imper- 
viousness  is  desirable. 

Willesden  paper  is  made  by  passing  the  web  through  a  strong 
solution  of  Schweitzer's  reagent  (copper  hydroxide  dissolved  in  strong 
ammonia),  and  pressing  together  several  sheets  so  prepared  without 
washing.  The  surface  of  the  cellulose  is  softened  and  the  sticky 
sheets  are  compacted  into  a  single  thick  one.  The  evaporation  of  the 
ammonia  leaves  the  cupro-cellulose  in  the  fibres,  which  a*e  thus 
coated  with  a  green  varnish-like  substance,  and  rendered  water-proof. 

Vulcanized  fibre  *  was  invented  by  an  English  chemist  named 
Taylor  about  the  year  1869.  Although  the  original  patents  included 
the  use  of  sulphuric  and  nitric  acids,  with  or  without  the  addition  of 
various  metallic  salts,  the  process  as  commercially  practised  to-day 
is  confined  to  the  action  of  zinc  chloride  on  pure  cotton  cellulose 
paper,  f  The  paper  is  passed  over  heated  cylinders  through  a  bath 
of  zinc  chloride  maintained  at  about  70°  Be.  and  40°  C.,  depending 
upon  the  quality  of  the  paper  and  the  atmospheric  conditions.  It  is 
then  rolled  up  over  large  heated  drums  -to  the  desired  thickness, 
the  zinc  chloride  hydrolyzing  the  cellulose  and  gelatinizing  the 
surface  to  such  an  extent  that  the  paper  unites  together  and  forms  an 
almost  homogeneous  mass:  Fibre  tubes  may  be  made  in  a  similar 
manner  by  substituting  for  the  large  drums  mandrels  of  the  proper 
size  to  give  the  desired  inside  diameter.  The  "  green  fibre  "  is  now 
washed  in  baths  of  zinc  chloride  of  progressively  diminishing  concen- 
tration until  it  is  entirely  pure,  when  it  is  dried  at  40°  to  60°  C.,  pressed, 
and  calendered.  The  finished  product,  which  has  shrunk  to  one-half 
its  original  thickness,  is  a  homogeneous,  tough,  hornlike  material, 
which  can  be  readily  machined,  threaded,  embossed,  etc.,  and  which 
can  be  given  a  high  polish.  It  may  be  rendered  flexible  by  soaking 

*  J.  Soc.  Chem.  Ind.,  1897,  552. 
tU.S.  Pat.,  114880. 


PAPER  567 

in  calcium  chloride  or  glycerine  solutions.  Some  of  its  more  important 
properties  are:  Specific  gravity,  1.2-1.5;  dielectric  strength,  100- 
175  kilo  volts  per  cm. ;  tensile  strength,  10,000-12,000  Ibs.  per  sq. 
in. ;  compressive  strength,  35,000-40,000  Ibs.  per  sq.  in. 

Vulcanized  fibre  is  used  for  all  kinds  of  electrical  insulation ;  for 
trunks,  roving  cans,  waste  baskets,  and  similar  receptacles ;  and  for  a 
great  variety  of  mechanical  purposes,  such  as,  gears,  valves,  washers, 
bushings,  etc. 

The  testing  of  paper  should  be  both  microscopical  and  chemical ; 
considerable  attention  is  given  to  this  on  the  continent  of  Europe, 
but  in  this  country  it  is  seldom  employed.  The  methods  and  details 
may  be  found  fully  described  in  Griffin  and  Little's  Chemistry 
of  Paper-Making,  Chap.  IX.,  and  in  the  works  of  Wiesner  and  of 
Herzberg. 

REFERENCES 

Die  Fabrikation  des  Papiers.     L.  Miiller,  Berlin,  1877. 

The  Manufacture  of  Paper.     C.  T.  Davis,  Philadelphia,  1882. 

Guide  pratique  de  la  Fabrication  du  Papier.     A.  Proteaux,  Paris,  1884. 

Handbuch  der  Papierfabrikation.     S.  Mierzinski,  Wien,  1886. 

Die  Microscopische  Untersuchung  des  Papiers.     J.  Wiesner,  Leipzig,  1887. 

Die  Fabrikation  des  Papiers.     E.  Hoyer,  Braunschweig,  1887.     (Vieweg.) 

Die  Bestimmung  des  Holzschliffes  im  Papier.     A.  Miiller,  Berlin,  1887. 

The  Practical  Paper  Maker.    J.  Dunbar.  3d  ed.    London,  1887.     (Spon.) 

Papier  Priifung.     W.  Herzberg,  Berlin,  1888.      (J.  Springer.) 

Le  Papier.     P.  Charpentier,  Paris,  1890.     (Tome  X.,  Encyclope  die  Chi- 

mique,  par  M.  Fremy.) 

The  Art  of  Paper  Making.     A.  Watt,  London,  1890. 
Technologie  der  Papier  Fabrikation.     Wurtemberg,  1893. 
The  Chemistry  of  Paper-Making.     R.  B.  Griffin  and  A.  D.  Little,  New 

York,  1894.     (Lockwood  &  Co.) 

United  States  Consular  Reports,  1894.     Parchment  Paper. 
A  Treatise  on  Paper-Making.     Carl  Hoffman,  New  York,  1895. 
A  Textbook  of  Paper  Making.      C.  F.  Cross  and  E.  J.  Bevan.      2d  ed. 

London,  1900.     (E.  and  F.  N.  Spon.) 

Paper  Trade  Journal,  New  York,  1893,  June  24,  et  seq. :  — 
Evolution  of  the  Sulphite  Digester.     H.  A.  Rademacher. 
Journal  of  the  Society  of  Chemical  Industry :  — 

1890,  Chemistry  of  Hypochlorite  Bleaching'.      C.  F.  Cross  and  E.  J. 

Bevan. 
1890,  9,  241,  Paper  Testing.     H.  Schlichter. 


GLUE 

Glue  is  the  first  product  of  the  hydrolysis  of  animal  connective  and 
elastic  tissues.  When  heated  with  water,  these  tissues  lose  their 
peculiar  structure,  swell,  and  finally  dissolve ;  on  cooling,  this  solution 
jellies  and  dries  into  a  horny,  translucent  mass,  which  is  the  glue. 
When  redissolved  in  hot  water,  this  forms  a  thick  solution  having 
strong  adhesive  properties.  Gelatine  is  made  more  carefully,  from 
better  stock,  but  chemically  there  is  no  difference  between  it  and 
glue.  Both  swell  with  cold  water,  but  do  not  dissolve  until  the  water 
is  heated. 

Glue  is  a  colloid,  a  water  "  solution  "  of  which  has  as  the  dispersing 
medium  a  dilute  solution  of  glue  (the  more  completely  hydrolized  part)  in 
water,  in  which  is  suspended  as  the  disperse  phase,  a  liquid,  or  more 
probably  a  semi-solid,  consisting  of  a  solution  of  water  in  glue.  The  more 
water  present,  the  greater  the  fraction  of  the  gelatine  dissolved  in  the  dis- 
persing medium,  and  the  less  in  the  disperse  phase.  At  high  tempera- 
tures (above  40°  to  50°  C.)  the  solubility  of  gelatine  in  water  is  so  great 
that  the  amount  present  as  disperse  phase  is  small,  but  as  the  temperature 
decreases,  this  phase  increases  at  the  expense  of  the  dispersing  medium, 
till  a  point  is  reached  at  which  the  components  interchange  functions,  the 
semi-solid  becoming  the  dispersing  medium,  and  the  residual  liquid  (largely 
water)  the  disperse  phase,  existing  as  drops  throughout  the  solid.  The 
system  is  now  called  a  jelly  or  gel,  and  the  temperature  of  transition  of  the 
given  solution,  its  jellying  point. 

Commercial  glue  from  any  source  contains  two  essential  constitu- 
ents, —  glutin,  an  amorphous,  odorless,  tasteless,  protein  substance, 
soluble  in  hot  water,  having  great  adhesive  strength,  and  precipitated 
from  solution  by  tannin  or  alcohol ;  and  chondrin,  similar  to  glutin, 
but  mainly  derived  from  the  cartilaginous  and  young  bonfe  tissues, 
and  having  less  adhesive  strength.  There  are  three  general  classes, 
hide  glue,  bone  glue,  and  fish  glue.  Hide  glue  is  made  from  glue 
stock,  i.e.  waste  bits  of  hide  trimmings,  skivings,  fleshings,  and  other 
untanned  refuse  from  the  beam  house ;  slaughter-house  waste,  such 
as  the  ear-laps  and  heads  (petes),  sinews,  feet,  and  tails  of  cattle  and 
sheep ;  and  the  skins  of  rabbits,  hares,  and  dogs,  and  scraps  of  alum- 
tawed  leather.  The  external  horny  parts  of  hoofs  and  horns  are  of 
no  value  as  glue  stock. 

The  stock,  wet,  or  dried  and  salted,  is  washed,  and  then  limed  for 
from  six  weeks  to  several  months,  during  which  time  it  is  thoroughly 

568 


GLUE  569 

and  frequently  stirred.  It  swells,  and  the  fats  are  converted  into 
lime  soap,  while  blood,  flesh,  and  coriin  are  partly  dissolved.  The 
stock  is  then  thoroughly  washed  in  tubs,  with  mechanical  stirrers,  or 
rollers,  to  remove  the  lime,  lime  soap,  and  dirt ;  the  last  trace  of  lime 
is  removed  by  treating  with  dilute  hydrochloric  acid,  or,  better,  with 
sulphurous  acid,  which  both  plumps  and  bleaches  the  stock.  The 
excess  acid  is  washed  away,  and  the  stock  is  ready  for  "  cooking  "  or 
"  boiling,"  to  convert  the  collagen  into  glue.  The  temperature  of 
heating  is  from  65°  to  100°  C.,  although  actual  boiling  of  the  liquor 
is  avoided.  The  kettles  are  open  wooden  vats,*  heated  by  closed 
steam  coils,  above  which  is  a  perforated  false  bottom  covered  with  a 
layer  of  excelsior  or  straw,  and  finally  an  iron  grating,  upon  which 
the  glue  stock  rests.  Water  is  added,  and  the  kettle  is  heated  until 
the  stock  dissolves,  forming  a  solution  thick  enough  to  jelly  on  cool- 
ing. Long  cooking  of  the  solution  must  be  avoided,  or  considerable 
decomposition  occurs  and  the  strength  of  the  product  is  decreased. 
The  grease  and  lime  soaps  rise,  and  are  skimmed  off;  the  solid 
matter,  consisting  of  hair,  etc.,  sinks,  and,  together  with  the  excelsior, 
forms  a  filter  through  which  the  liquor  is  drawn  off  from  under  the 
false  bottom,  and  a  clear  solution  is  obtained ;  or  the  liquor  may  be 
filtered  on  felt  or  in  bag  filters. 

The  stock  is  not  all  dissolved  in  the  first  liquor,  and  usually  from 
three  to  five  boilings  with  fresh  water  are  necessary  to  extract  all  the 
glue ;  these  later  solutions  are  thicker  and  stronger,  so  all  the  liquors 
are  usually  mixed,  except  the  first,  which  yields  the  finest  product. 
Sometimes  the  stock  is  treated  in  closed  kettles  with  direct  steam 
under  pressure,  thus  causing  rapid  melting. 

If  the  liquor  is  too  thin  to  jelly,  it  is  concentrated  in  a  vacuum 
pan.  The  solution  is  run  into  coolers,  which  differ  in  size  and  shape. 
A  good  form  is  a  galvanized  iron  or  aluminum  pan  13  inches  long  by 
11  inches  wide  by  9  inches  deep,  and  having  slightly  flaring  sides. 
This  is  cooled  by  standing  in  cold  water,  or  by  the  use  of  refrigerating 
machines. 

In  from  12  to  24  hours  the  solution  jellies,  forming  a  mass  con- 
taining about  85  per  cent  water.  This  is  turned  out  on  a  table 
and  cut  into  plates  from  one-eighth  to  one-fourth  of  an  inch  thick, 
by  means  of  wires  stretched  tightly  across  a  frame.  These  slices 
must  be  carefully  dried  at  once;  they  are  put  in  single  layers  on 
wire  frames  and  passed  into  the  dry-room,  a  long,  narrow  room  from 
which  sunlight  is  excluded,  and  which  is  heated  by  hot  air,  blown 
*  Tinned  metal  kettles  are  sometimes  used  instead  of  wooden  vats. 


570  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

in  at  the  end  farthest  from  where  the  glue  enters.  The  jelly  is  very 
apt  to  develop  mould  or  to  liquefy  through  the  action  of  bacteria, 
while  if  the  temperature  rises  over  35°  to  40°  C.,  it  is  liable  to  melt, 
forming  a  "  daub."  But  in  clear,  cold  weather,  the  temperature  of 
the  dry-room  may  rise  to  43°  C.  In  summer  it  is  nearly  impossible 
to  dry  the  films  properly  and  no  glue  is  made.  If  the  wet  film  is 
frozen  and  then  dried,  the  glue  is  spongy  and  porous.  The  glue 
should  dry  in  about  24  hours,  when  the  trays  are  removed  from  the 
hot  end  of  the  drying-room,  and  the  films  broken  or  ground  in  a  dis- 
integrator and  packed  for  shipment.  The  dry  glue  contains  about  15 
per  cent  water. 

Bone  glue  is  not  essentially  different  from  hide  glue,  and  is  made 
from  green  bones  which,  for  the  better  qualities,  must  be  quite  fresh. 
They  are  boiled  with  water,  and  the  oily  matter  skimmed  off  as 
it  rises;  or  better,  the  bones  are  extracted  with  benzine  or  other 
solvent,  in  a  "  rendering  tank,"  p.  354.  The  extracted  bones  are 
crushed  and  treated  with  dilute  hydrochloric  acid  (sp.  gr.  1.05) 
until  the  calcium  phosphate  and  other  salts  dissolve.  The  cartilagi- 
nous residue  is  treated  with  lime-water  to  remove  any  acid.  After 
washing,  the  mass  is  boiled  with  water  or  steamed  in  a  digester 
until  dissolved.  Any  grease  is  skimmed  or  filtered  off  and  the 
gelatine  is  chilled  and  dried  as  already  described.  Benzine-extracted 
bones  are  often  crushed  and  boiled  directly  or  steamed  for  glue. 
The  glue  solution  is  then  strained  through  a  cloth,  bleached  by 
treatment  with  sulphurous  acid,  and  evaporated  at  about  60°  C. 
in  vacuo,  or  in  open  troughs  with  a  rotary  steam-coil  half  submerged 
in  the  liquid.  The  thick  solution  is  chilled,  jellied,  and  dried  as 
above. 

Fish  glue  is  made  by  boiling  the  heads,  fins,  and  tails  of  fish 
at  110°  C.  It  has  very  weak  jellying  properties  and  is  generally 
made  into  liquid  glue,  the  disagreeable  odor  being  destroyed  by 
adding  creosote,  oil  of  sassafras,  or  other  strong-smelling  substance. 

Liquid  glue  is  made  by  treating  fish  or  common  glue  with  acetic, 
nitric,  or  hydrochloric  acid,  whereby  the  property  of  gelatinizing 
when  cold  is  lost.  But  the  adhesiveness  is  not  materially  changed; 
and  since  such  glues  do  not  require  to  be  heated  or  applied  to  hot 
surfaces,  they  are  extensively  used. 

Gelatine  is  prepared  from  calf  or  sheep  skin  and  from  sturgeon 
and  other  fish  skin.  The  first  liquors  formed  in  the  boiling  or  steam- 
ing yield  a  colorless  gelatine  which  is  used  for  food  and  in  the  prepa- 
ration of  photographic  emulsions.  The  solution  is  often  filtered  on 


GLUE  571 

bone-black  or  bleached  with  sulphur  dioxide  before  jellying.  Much  is 
used  in  clarifying  liquors  containing  tannins,  especially  wines,  etc. 

Isinglass  is  a  pure  white,  odorless,  tasteless  gelatine,  prepared  by 
drying  the  inner  skins  of  the  swimming  bladders  of  fish.  The  degree 
of  molecular  association  is  not  sufficient  to  require  a  preliminary  hy- 
drolysis, as  in  the  case  of  ordinary  glue  stock.  It  is  almost  entirely 
soluble  in  water  at  about  50°  C.,  and  forms  a  transparent  jelly  on 
cooling.  Owing  to  its  high  price  and  slight  adhesive  strength,  it  is 
used  only  for  food  and  in  clarifying  liquors,  such  as  wine,  beer,  coffee, 
etc. 

A  vegetable  gelatine  derived  from  a  species  of  algse  or  seaweed 
forms  the  agar-agar,  p.  400,  or  Bengal  isinglass  of  commerce. 

Satisfactory  methods  for  glue  testing  have  not  yet  been  devised. 
The  usual  tests  are  determinations  of  the  viscosity  of  the  solution  and 
the  firmness  of  the  jelly  formed,  but  the  adhesiveness  does  not  de- 
pend upon  the  quality  of  the  jelly.  Glue  is  usually  sold  according 
to  its  color  and  physical  properties,  and  should  be  free  from  grease. 

REFERENCES 

Die  Fabrikation  chemischen  Producte  aus  thierisehen  Abf alien.    H.  Fleck, 

Braunschweig,  1878. 

Die  Leim  und  Gelatin  Fabrikation.    2te  Auf.    F.  Dawidowsky,  Wien,  1879. 
Glue  and  Gelatine.    Dawidowsky-Brannt,  Philadelphia,  1884.     (Baird.) 
Cements,  Pastes,  Glues,  and  Gums.     H.  C.  Standage,  London,  1893. 


LEATHER 

The  skin,  when  removed  from  the  animal,  very  soon  becomes 
putrid  if  kept  moist,  and  is  hard  and  horny  when  dried;  in  either 
case,  boiling  water  converts  it  into  soluble  glue.  Leather  is  skin  so 
treated  that  it  remains  more  or  less  soft  and  pliable,  does  not  putrefy, 
and  is  not  readily  changed  into  glue.  Animal  skins  are  made  up  of 
three  layers,  —  the  epidermis,  the  fatty  tissues,  and  between  them 
the  corium,  cutis,  or  skin  proper.  The  epidermis  is  thin  and  the 
roots  of  the  hair  are  attached  to  it.  It  consists  of  individual  cells, 
which  become  dead  and  dry  on  the  outer  surface,  and  are  easily  de- 
tached by  friction  or  abrasion.  These  cells  are  largely  composed  of 
keratin,  a  substance  rich  in  sulphur,  and  very  little  affected  by  cold 
water;  even  hot  water  does  not  produce  gelatine  from  it.  But  the 
young,  interior  cells  are  somewhat  attacked  by  lime-water.  The 
hair  and  keratin  substances  are  dissolved  by  concentrated  alkali  and 
especially  alkaline  sulphide  solutions.  The  fatty  tissues  form  the 
innermost  layer  of  the  skin,  and  consist  of  a  loose  network  of  con- 
nective tissue,  containing  fat  cells,  blood  vessels,  sudorific  glands,  and 
muscular  fibres.  The  ducts  of  the  sweat  glands  pass  through  the 
corium  and  epidermis. 

The  corium  or  dermis  is  the  only  part  of  the  skin  of  value  for 
leather;  it  consists  of  connective  tissue  composed  of  bundles  of 
fibres  which  interlace  somewhat  loosely  on  the  under  side  of  the  skin, 
but  are  closely  matted  on  the  epidermal  side.  This  fibrous  substance 
consists  chiefly  of  collagen,  which  appears  to  be  altered  by  the  action 
of  boiling  water  and  converted  into  soluble  gelatine  or  glue.  Some 
authorities  hold  that  an  intercellular  substance,  coriin,  comparable 
to  sericine  or  silk  glue,  p.  492,  fills  the  spaces  between  the  bundles  of 
fibres,  and  cements  them  together  when  the  skin  dries,  making  the 
skin  hard  and  stiff.  Other  writers  regard  the  coriin  as  merely  an 
alteration  or  decomposition  product  of  collagen.  Both  collagen  and 
coriin  are  albuminoids,  complex  condensation  products  of  amino- 
acids,  capable  of  progressive  hydrolysis,  the  ultimate  product  being 
the  simple  acids.  This  hydrolysis  takes  place  even  in  cold  water, 
though  slowly,  but  is  greatly  accelerated  by  heat,  by  electrolytes 
(especially  acids  in  proportion  to  their  strength,  i.e.  H+  ion  concen- 
tration), and  by  various  enzymes.  The  first  effect  of  the  hydrolysis 
is  a  mechanical  weakening  of  the  fibre,  rapidly  followed  by  solution 

572 


LEATHER  573 

(conversion  to  glue),  and  ultimately  resulting  in  the  production  of  the 
component  amino-acids.  Coriin  is  the  more  readily  hydrolyzed,  and 
is  perhaps  the  first  product  of  the  hydrolysis  of  collagen. 

The  tannage  of  leather  consists  in  the  separation  of  the  cutis  from 
the  accompanying  tissues,  the  conversion  of  it  into  an  insoluble  form, 
and  the  subsequent  treatment  or  finishing  of  the  leather  to  secure  the 
necessary  body  and  appearance. 

Hide  substance  is  an  organized  gel  (pp.30;  568),  the  solid  dispersing 
medium  being  the  fibre  bundles  of  the  skin,  the  liquid  dispersed  phase  being 
perhaps  the  contents  of  the  individual  cells  ;  the  latter  contain  in  true  solu- 
tion hydrolysis  products  of  the  collagen,  the  less  complex  condensation 
products  of  amino-acids  which  are  amphoteric  (since  they  contain  both 
free  amino  and  carboxyl  groups),  and  therefore  react  with  both  acids  and 
bases,  the  basic  character  being  somewhat  the  stronger.  The  collagen 
of  the  dispersing  medium  is,  in  its  normal  state,  highly  hydrated,  elastic, 
and  semi-permeable  (allowing  almost  perfect  diffusion  of  strong  inorganic 
electrolytes),  but  is  entirely  impervious  to  the  amphoteric  contents  of  the 
cells,  whether  ionized  or  not.  Like  all  albumins  and  the  so-called  emul- 
soids  or  emulsion  colloids,  it  is  readily  dehydrated,  either  by  drying,  by 
the  action  of  strong  solutions  of  electrolytes,  or  by  coprecipitation  with 
other  emulsoids.  When  thus  dehydrated,  it  shrinks  and  loses  its  elasticity. 
It  is  also  readily  hydrolyzed  to  less  and  less  complex  products,  the  reaction 
being  hastened  especially  by  hydrogen  ion  and  by  heat,  but  also  by  hy- 
droxyl  and  various  enzymes.  Any  acidic  or  basic  groups  in  the  collagen 
are  exceedingly  weak,  as  is  to  be  expected  from  its  complex  structure. 
The  conversion  of  hide  into  leather  consists  in  the  dehydration  of  the  col- 
lagen by  coprecipitation  with  other  emulsoids.  To  secure  penetration 
and  uniformity  of  action  the  precipitating  colloid  must  be  in  solution  and 
the  collagen  itself  must  be  completely  and  uniformly  hydrated. 

Pelts  are  divided  by  the  tanner,  according  to  their  size,  into  three 
classes :  (a)  hides,  comprising  the  skins  from  large  and  fully  grown 
animals,  such  as  the  cow,  ox,  horse,  buffalo,  walrus,  etc. ;  these  form 
thick,  heavy  leather,  used  for  shoe  soles,  machinery  belting,  trunks, 
and  other  purposes  where  stiffness  and  strength,  combined  with  great 
wearing  properties,  are  essential ;  (6)  kips,  the  skins  from  undersized 
animals  or  yearlings  of  the  above  species;  (c)  skins  obtained  from 
small  animals,  such  as  calves,  sheep,  goats,  dogs,  etc.  These  yield 
lighter  leather  suitable  for  a  great  variety  of  purposes.  The  thickest 
and  heaviest  hides  come  from  rough,  sparsely  settled  countries.  The 
same  hide  varies  in  thickness  and  texture  in  different  parts,  being 
thicker  on  the  neck  and  butt  than  on  the  flank  and  belly.  They  fre- 
quently show  injury,  such  as  cuts,  brand  marks,  and  holes  or  thin 
places  caused  by  the  bot-fly  or  warble.  Diseased  pelts  are  often  sold, 


574  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

which,  besides  yielding  a  poor  leather,  are  a  source  of  danger  to  the 
workmen,  owing  to  the  contagious  nature  of  some  of  the  diseases 
(especially  anthrax) ;  hence  disinfectants  should  be  freely  used  in  the 
tannery. 

Pelts  come  to  the  tanner  "  green  "  (fresh  from  the  animal),  salted 
(where  the  salt  has  been  thickly  rubbed  on  the  flesh  side),  or  dried. 
Green  pelts  are  washed  in  clear  water  to  free  them  from  blood  and 
dirt ;  salted  pelts,  if  not  dried,  are  merely  washed  in  several  changes 
of  water.  It  is  essential  to  remove  all  the  salt  before  beginning  the 
unhairing  process,  as  it  retards  the  action  of  the  lime  and  interferes 
with  the  "  plumping  "  of  the  skin.  It  is  also  liable  to  cause  an  efflores- 
cence ("  spueing  ")  on  the  finished  leather.  Dried  hides  must  be 
thoroughly  rehydrated  by  soaking  in  water,  using  care  to  secure  uni- 
formity. Luke-warm  water,  or  the  liquor  from  the  soaking  of  a  pre- 
vious lot,  may  be  used  to  promote  fermentation,  resulting  in  the  pro- 
duction of  ammonia  and  amines,  but  the  use  of  this  "  putrid  soak  " 
must  be  carefully  watched  to  prevent  putrefactive  injury  to  the  skin ; 
more  often  in  modern  practice,  soda-ash,  borax,  or  sodium  sulphide 
are  added  *  in  small  amounts  to  the  soak.  Acids  cannot  be  used  for 
softening,  on  account  of  the  destruction  of  the  fibre  by  hydrolysis  in 
the  presence  of  hydrogen  ion.  After  hydration  is  sufficient  so  that 
the  hide  may  be  bent  double  without  breaking,  it  is  furthered  by 
mechanical  working,  by  tumbling  (submerged  in  water)  in  drums, 
or  by  mauling  in  "  stocks  "  or  mills  with  wooden  mauls  or  rollers. 

The  character  of  the  water  used  in  the  tannery  is  important. 
Soft  water  makes  the  skins  thin  and  slim,  which  is  desirable  in  light 
leather.  Water  containing  calcium  or  magnesium  sulphate  "  plumps  " 
or  swells  the  hide,  thus  exposing  a  larger  surface  to  the  action  of  the 

*  The  probable  action  of  these  alkalies  in  assisting  hydration  is  as  follows : 
As  soon  as  hydration  begins,  there  is  within  the  cell,  as  the  disperse  phase,  a  solu- 
tion of  a  body  which  may  be  represented  by  a  general  formula,  NEb  •  B  •  COOH, 
where  B  indicates  an  organic  complex.  With  alkalies  this  reacts  : 

NH2  -  B  .  COOH  +  Na+  +  OH-  -^  NH2 .  B  :  COO-  +  Na+  +  H2O. 

The  dilute  solution  of  the  sodium  salt  of  this  acid  is,  like  all  such  salts,  almost  com- 
pletely dissociated,  and  since  the  anion  cannot  diffuse  through  the  dispersing 
medium,  its  corresponding  sodium  ion  is  held  in  the  cell  by  electrostatic  attraction. 
Fresh  alkali  will  enter  the  cell  by  diffusion  to  replace  that  consumed  by  the  reac- 
tion. This  reaction  in  consequence  of  the  production  of  a  highly  dissociated  salt 
in  place  of  an  undissociated  acid  (two  mols  derived  from  one) ,  has  therefore  doubled 
the  molecular  concentration  of  non-diffusible  material,  and  hence  doubled  the  net 
osmotic  pressure  in  the  cell,  which  results  in  its  distention.  This  distention  opens 
up  the  fibres  of  the  hide  and  draws  through  them  the  water  necessary  for  the  increase 
in  size  of  the  cell,  which  greatly  promotes  the  hydration  of  the  collagen. 


LEATHER  575 

tan  liquors,  which  is  desirable  for  heavy  hides.  Chlorides  cause  the 
hides  to  "  fall,"  i.e.  to  become  thin  and  flabby.  This  is  due  to  the 
dehydrating  action  of  the  electrolyte.  If  used  for  washing  after 
the  liming,  water  having  temporary  hardness  tends  to  fix  the 
lime  among  the  fibres  in  an  insoluble  form,  thus  causing  the  leather 
to  be  harsh  on  the  grain  and  producing  colored  spots  because  of  un- 
equal deposits  of  tannin  and  coloring  matters  in  the  tan  pits.  Hard 
water  also  causes  waste  of  tannin  matters  through  the  formation  of 
insoluble  compounds  with  lime  and  magnesia.  Water  carrying  organic 
impurities  may  have  an  acid  nature  and  cause  the  hides  to  "  fall " 
after  liming,  or  it  may  engender  putrefactive  changes  in  the  skin. 

When  thoroughly  cleaned  and  softened,  the  hides  undergo  the 
depilation  or  unhairing  process.  This  removes  the  hair  and  epider- 
mis, and  also  the  fatty  tissues  from  the  under  side  of  the  skin.  It  is 
done  by  treatment  with  an  alkaline  'solution,  which  attacks  and  soft- 
ens the  inner  layers  of  epidermal  cells,  loosening  the  outer  layer  and 
hair,  so  that  they  may  be  scraped  away  ;  or  by  "  sweating,"  in  which 
the  young  epidermal  cells  are  softened  by  bacterial  action  until  the 
outer  layers  are  loosened.  Lime  is  the  most  common  unhairing 
material,  sometimes  aided  by  the  addition  of  sodium  sulphide,  arsenic 
compounds,  or  calcium  hydrosulphide.  Skins  are  sometimes  un- 
haired  by  dilute  solution  of  sodium  sulphide,  which  dissolves  the  hair 
completely ;  this  cannot  be  used  if  the  hair  is  to  be  saved  as  by- 
product, and  care  is  needed  to  prevent  injury  to  the  skins. 

Liming.  —  The  skins  are  laid  in  a  vat  or  pit  with  milk  of  lime, 
which  loosens  the  epidermis  and  forms  a  soap  with  the  fatty  matter. 
It  also  dissolves  the  coriin,  loosening  the  fibres,  which  swell  and 
"  plump  "  the  hides.  It  is  used  in  excess  in  amounts  varying  from 
one-half  pound  for  a  small  light  skin  to  4  pounds  for  a  heavy  one. 
The  vats  or  pits  when  prepared  to  receive  the  skins  are  called  "  limes." 
The  skins  are  frequently  turned  over  and  worked  about  ("  handled  ") ; 
for  heavy  hides  which  are  to  form  stiff,  hard  leather,  the  liming  only 
lasts  a  few  days ;  but  for  a  soft,  elastic,  pliable  product,  the  process 
continues  for  15  or  20  days,  or  longer.  Warming  the  limes  to  85°  or 
90°  F.  hastens  the  action,  but  causes  the  skins  to  "  fall."  The  addi- 
tion of  sodium  sulphide  to  a  thick  cream  of  lime  yields  a  paste 
which  may  be  spread  on  the  hair  side  of  the  skin,  and,  after  being 
folded  together  for  a  few  hours,  the  hair  is  easily  detached. 
Arsenic  sulphides,  realgar  and  orpiment  (about  10  per  cent  of  the 
weight  of  the  lime),  are  frequently  added  to  the  limes,  forming  calcium 
sulph-arsenite  (HCaAsS3),  which  is  a  rapid  depilatory. 


576  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

"  Sweating  "  is  used  for  hides  which  are  to  be  made  into  sole  or 
other  stiff  leather.  The  hides  are  hung  in  a  room  kept  at  a  constant 
temperature  of  18°  to  21°  C.,  the  atmosphere  being  saturated  with 
moisture.  Bacterial  decomposition  of  the  inner  layer  of  the  epider- 
mis sets  in  and  after  a  few  days  the  hair  is  loosened.  The  bacteria 
which  are  effective  in  sweating  are  aerobic ;  the  putrefactive  bacteria 
are  anaerobic,  hence  decomposition  of  the  fibre  can  be  controlled  by 
providing  an  adequate  air  supply.  Before  treating  with  tannin, 
sweated  hides  must  be  "  plumped  "  by  immersion  in  dilute  acid. 

After  the  hair  has  been  loosened,  the  skin  is  laid  across  a  sloping 
"  beam  "  of  wood,  and  the  hair  and  epidermis  are  scraped  away  with 
a  blunt  knife.  The  fatty  tissues  are  removed  in  the  same  way. 
These  operations,  known  as  "  beaming,"  are  carried  on  in  the  "  beam 
house  "  of  the  tannery.  After  trimming  off  the  waste  parts  of  the 
skin,  it  is  thoroughly  washed,  and  is  usually  again  scraped  on  the 
"  beam  "  (scudded)  to  remove  as  much  of  the  lime  as  possible. 

If  soft,  pliable  leather  is  to  be  made,  the  skins  are  next  subjected 
to  the  "  bating,"  or  "  puering,"  process  to  destroy  the  "  plumping  " 
produced  by  the  lime,  and  also  to  cause  other  changes,  the  nature 
of  which  is  rather  obscure.  Some  authorities  claim  that  the  bate 
merely  removes  the  lime  from  the  pores  of  the  hide,  while  others 
assert  that  it  also  takes  away  some  of  the  coriin,  thus  leaving  the 
fibres  looser,  and  allowing  more  perfect  action  of  the  tan  liquors. 
The  latter  view  seems  probable,  and  there  is  little  doubt  that  the 
bacteria  in  the  bate  do  feed  upon  the  hide  substance.  Further, 
the  ferments,  tripepsin,  pancreatin,  etc.,  present,  undoubtedly  exer- 
cise some  function,  for  when  used  alone  they  will  cause  a  "  plumped  " 
skin  to  fall.  The  ammonium  salts  formed  doubtless  also  assist  in 
the  solution  of  the  lime  in  the  skin.  Bating  consists  in  soaking  the 
hides  in  a  mixture  of  dog  or  bird  dung  in  warm  water.  This  quickly 
becomes  putrid,  and  evolves  hydrogen  sulphide,  while  the  liquor 
acquires  an  alkaline  reaction.  The  process  lasts  from  2  to  4  days, 
according  to  the  thickness  of  the  skin  and  the  temperature.  It  is 
largely  dependent  upon  the  atmospheric  conditions;  in  the  warm, 
sultry  weather,  such  as  usually  precedes  a  thunder-storm  in  this 
climate,  the  action  becomes  extremely  rapid,  and  a  few  hours  is  often 
sufficient  to  injure  the  skin.  Great  care  must  be  exercised  at  all 
times,  and  the  skins  stirred  about  frequently  to  prevent  too  great 
local  action,  resulting  in  thin  places  or  in  holes  in  the  leather. 

Many  proposals  have  been  made  to  replace  the  offensive  bate  with 
pure  solutions  of  weak  mineral  and  organic  acids;  but  these  have 


LEATHER  577 

not  generally  found  favor  with  tanners,  the  common  objection  being 
that  the  leather  is  made  harsh,  and  has  a  bad  grain. 

After  bating,  the  fibres  have  become  soft  and  pliable,  and  the 
whole  skin  has  a  smooth,  slippery  feel.  As  these  qualities  are  not 
desirable  in  sole  leather,  heavy  hides  are  not  bated. 

In  order  to  complete  the  removal  of  the  lime,  it  is  customary  to 
next  pass  the  skins  into  the  "  bran  drench,"  consisting  of  an  infusion 
of  bran  and  water  at  a  temperature  of  about  32°  C.  On  standing, 
this  soon  develops  a  fermentation,  in  which  lactic  with  some  butyric 
and  acetic  acids  are  formed,  dissolving  the  lime. 

The  skins  are  now  ready  for  actual  conversion  into  leather,  or 
the  tanning  process.  This  is  done  in  three  ways :  — 

(1)  With  tannin  in  any  form  (vegetable  tannage). 

(2)  With  metallic  salts  (mineral  tannage). 

(3)  With  oils  or  fats  (oil  tannage). 

1.  The  sources  of  vegetable  tannins  have  been  considered  on  p. 
518.  For  leather,  it  has  been  found  essential  that  the  tannin  material 
shall  yield  other  extractive  matters  than  tannic  acid  when  treated 
with  water.  These  non-tannins  are  mainly  sugars,  gums,  resins,  and 
coloring  matters.*  They  assist  in  the  tanning  in  several  ways,  — 
some  of  them  are  directly  absorbed  by  the  skin,  increasing  its  weight 
and  solidity ;  others  set  up  fermentations  in  the  tan  pit,  producing 
organic  acids  which  assist  in  the  formation  of  a  leather  of  a  good  body 
and  weight.  The  tan  liquors  are  prepared  by  systematic  lixiviation 
of  the  ground  tan-stuffs,  the  strongest  liquors  coming  in  contact 
with  the  freshly  ground  material.  The  temperature  is  important, 
warm  water  being  generally  best  for  complete  extraction,  although 
gambier  requires  cold  water.  The  spent  tan  is  usually  burned  for 
fuel.  Extracts,  alone  or  in  conjunction  with  tan  liquors,  are  becom- 
ing more  generally  used.  They  are  simply  dissolved  in  water,  and 
may  be  added  as  needed ;  but  they  are  often  adulterated  with  glucose 
or  molasses,  consequently  tests  with  the  barkometer  f  are  of  no  value 
unless  the  material  is  known  to  be  pure. 

Vegetable  tanning  is  used  for  sole  leather,  upper  leathers,  and 
colored  leathers  (morocco).  Sole  leather  is  heavy,  solid,  and  stiff, 
but  may  be  bent  without  cracking.  For  this,  tanning  materials  such 
as  oak  or  hemlock  bark,  mimosa,  chestnut  wood,  quebracho,  valonia, 

*  The  tannins  derived  from  gallic  acid  cause  a  white  efflorescence  (ellagic  acid) 
on  the  leather,  while  those  of  the  protocatechuic  acid  group"  deposit  red  coloring  mat- 
ters (phlobaphenes)  in  it. 

t  A  special  form  of  hydrometer  for  determining  the  strength  of  tan  liquors. 
2p 


578  OUTLINES   OF    INDUSTRIAL   CHEMISTRY 

and  myrabolans  are  used.  The  hides  ("  butts  ")  are  first  hung  from 
frames  in  pits  (suspenders),  containing  weak  or  nearly  spent  tan 
liquors  from  a  previous  lot.  Here  they  are  mechanically  agitated,  by 
rocking  the  frames  so  that  the  hides  take  up  the  tannin  evenly. 
Every  few  days  they  are  transferred  ("handled  ")  into  pits  containing 
stronger  liquor,  until,  after  two  weeks,  the  hides  are  brought  into  full 
strength  solutions.  If  treated  with  too  strong  liquor  at  first,  the 
surface  would  be  so  hardened  that  thorough  penetration  into  the 
interior  of  the  hides  could  not  take  place.  The  partially  spent  liquors 
are  transferred,  according  to  the  counter-current  principle,  from  each 
pit  into  the  next  succeeding  containing  hides  which  have  taken  up 
less  tannin.  The  hides  are  then  put  into  the  "  layers,"  i.e.  pits  in 
which  the  hides  are  spread  flat,  sprinkled  with  ground  tanstuff  (bark, 
valonia,  etc.),  and  strong  liquor  (ooze)  at  25°  barkometer  is  run  in 
until  the  pack  is  submerged.  After  7  or  8  days,  the  hides  are  taken 
out,  brushed  clean,  and  again  "  laid  away  "  in  fresh  tan  and  stronger 
liquor,  to  remain  12  to  14  days ;  the  process  is  repeated  with  about 
20  days'  submergence,  and  finally  about  4  weeks'  "  laying  away  "  in 
full  strength  liquor  at  40°  barkometer  and  fresh  ground  tan  completes 
the  process.  Frequently  the  temperature  of  the  liquor  in  the  "  layers  " 
is  progressively  raised  from  about  70°  F.  in  the  first  to  90°  or  100°  F. 
in  the  last.  Thus  the  whole  tanning  treatment  requires  about  3 
months  or  more,  for  heavy  sole  leathers;  (it  may  be  hastened  by 
keeping  the  liquors  in  constant  circulation,  or  by  continual  movement 
of  the  hides  and  using  strong  extracts. 

Various  electrical  tannage  processes  have  been  devised,  but  these 
have  generally  proved  failures  in  use. 

Sole  leather  is  usually  finished  by  brushing  and  washing,  followed 
by  slow  drying ;  the  drying  is  retarded  by  oiling  the  leather  several 
times  on  the  grain.  When  partly  dry,  it  is  "sammied"  by  piling  in 
a  heap  and  covering  until  heating  is  induced.  It  is  then  "  struck 
out,"  i.e.  stretched  by  working  with  a  triangular  tool  having  blunt 
edges,  or  by  rolling  with  a  heavy  roller  under  pressure  in  a  machine. 
The  weight  of  the  leather  is  sometimes  increased  by  impregnating  it 
with  glucose,  or  with  barytes  or  other  mineral  salts.  Dry  hides 
yield  about  180  per  cent  of  their  weight  in  leather,  while  green  hides 
make  only  about  55  per  cent. 

Upper  or  dressed  leather  is  made  from  kips  and  large  calf  skins. 
After  bating,  the  skin  is  usually  shaved  on  the  flesh  side  to  make  it  of 
uniform  thickness.  It  is  then  tanned  and  the  grain  hardened  by  hand- 
ling or  tumbling  in  revolving  boxes  or  drums,  in  a  rather  strong  solu- 


LEATHER  579 

tion  of  tan  liquor,  usually  prepared  from  gambier.  The  tannage  is  com- 
pleted with  mimosa,  myrabolans,  valonia,  or  bark,  the  liquors  sometimes 
being  heated  to  50°  or  60°  C.  and  a  final  tumbling  in  sumach  liquor. 

Leather  is  finished  by  a  process  called  currying.  That  is,  it 
is  first  scoured  with  brushes  and  then  rubbed  with  a  "sleeker,"  a 
smooth  stone  or  piece  of  glass  which  removes  the  creases  and  wrinkles 
and  stretches  the  leather.  It  is  then  "  stuffed  "  with  a  mixture  of 
oil,  soap,  and  tallow,  which  is  worked  into  it  by  rolling  or  tumbling 
in  a  drum.  Olive,  neat's-foot,  sperm,  and  fish  oils  are  much  used  for 
this,  as  is  also  degras  (p.  581).  Upper  leathers  are  usually  blacked  by 
rubbing  with  a  mixture  of  lampblack  and  oil  or  tallow ;  or  they  may 
be  painted  with  a  solution  of  copperas  and  logwood. 

Colored  leather  is  made  chiefly  from  goat,  sheep,  and  calf  skins. 
These  are  limed,  unhaired,  bated,  and  drenched  as  above  described, 
and  are  tanned  with  gambier  or  sumach  liquors,  in  tumblers  or  drums, 
or  in  tubs,  or  handlers  where  they  are  kept  in  motion. 

Colored  leathers  are  usually  dyed  with  basic  dyestuffs  or  with 
natural  dyewood  extracts,  particularly  logwood.  After  tanning,  they 
are  passed  into  a  bath  of  tartar  emetic  to  fix  the  tannin  before  dyeing. 
The  dyeing  is  done  in  slightly  warm  baths,  as  hot  liquors  are  in- 
jurious. The  skin  is  folded  down  the  middle  with  the  grain  side  out, 
and  is  then  laid  in  a  slightly  warm  solution  of  the  dye  in  a  shallow 
tray ;  or  the  skin  may  be  sponged  with  the  dye  on  the  grain  side  while 
spread  on  a  table.  If  it  is  to  be  dyed  through,  it  is  worked  with  the 
dye  solution  in  a  tumbler  or  paddle-wheel. 

After  bating  or  when  partially  tanned,  the  skins  are  usually  split 
into  two  or  three  layers,  by  a  sharp  knife  driven  by  machinery.  The 
grain  side  is  finished  to  form  "  skivers,"  while  the  flesh  side  is  made 
into  patent  leather,  wash  leather  (chamois),  or  into  cheap  leather 
with  an  artificial  grain.  The  very  thin  grain  splits  from  sheep  and 
calf  leather  are  used  for  book  bindings.  The  flesh  splits  are  often 
given  an  artificial  grain  ("  pebbled  "),  by  rolling  with  an  engraved 
roll,  or  with  a  die  under  heavy  pressure.  This  imitation  may  be 
carried  so  far  as  to  make  small  punctures  in  the  leather  with  fine  pin 
points  to  resemble  the  pores  and  hair  sheaths  of  the  natural  grain. 
Or  an  electrotype  may  be  made  from  a  piece  of  natural  leather,  and 
this  copy  fixed  on  the  die. 

2.  Tanning  with  metallic  salts,  or  tawing,  is  employed  for  small 
skins  and  light  leathers,  and  is  very  important  in  this  country; 
the  salts  used  are  aluminum  and  chromium  compounds,  especially 


580  OUTLINES   OF    INDUSTRIAL   CHEMISTRY 

sulphates,  chlorides,  and  bichromates.  Alum  (or  aluminum  sulphate) 
is  employed  (in  conjunction  with  common  salt)  for  white  and  kid 
leathers.  After  liming,  usually  with  the  addition  of  arsenic,  for  three 
or  four  weeks,  and  unhairing  and  fleshing,  the  skins  are  thoroughly 
bated,  drenched,  and  scudded.  For  white  leather,  the  split  skins  are 
tumbled  in  a  drum  with  a  solution  of  alum  and  salt,  and  after  lying 
folded  several  hours  are  dried  without  washing.  The  hard  skin  is 
then  softened  by  pounding,  rolling,  and  stretching.  Kid  leather  for 
gloves,  and  calf  kid  are  made  by  tumbling  or  treading  the  split  skins 
in  a  mixture  of  alum,  salt,  flour,  egg-yolk,  and  olive  oil,  until  they 
are  thoroughly  impregnated,  and  then  drying.  The  leather  is  colored 
with  natural  or  coal-tar  dyes,  and  is  usually  again  tumbled  in  the 
salt  and  egg-yolk  emulsion.  It  is  softened  by  "  staking,"  i.e.  pulling 
across  the  edge  of  a  blunt  knife  fixed  in  a  vertical  position  in  a  post. 
The  flesh  side  is  shaved,  and  the  grain  glazed  or  polished  by  rubbing 
with  a  sleeker,  or  in  a  glazing  machine. 

Excellent  leather  is  produced  by  combining  the  alum  tanning 
process  with  tannage  in  gambier  liquor,  the  method  being  known 
as  the  combination  tannage,  or  dongola  process.  This  is  much  used 
for  making  leather  resembling  kid,  but  stronger  and  cheaper,  which  is 
largely  used  for  ladies'  shoes.  The  prepared  skins  are  tawed  in  alum 
and  salt  and  then  laid  in  gambier  liquor  for  several  days  or  a  week. 

Chrome  tannage,  or  tawing  with  chromium  salts,  has  been  chiefly 
developed  in  this  country  and  is  in  general  use  here.  The  principle 
of  the  process  consists  in  precipitating  an  insoluble  chromium  hydrox- 
ide or  oxide  on  the  fibres  of  a  skin  which  has  been  impregnated 
with  a  soluble  chromium  salt,  usually  potassium  bichromate ;  basic 
chromium  chloride,  chromium  chromate,  and  chrome  alum  are  also 
used.  The  skins,  having  been  limed,  unhaired,  fleshed,  bated, 
drenched,  and  scudded,  are  worked  in  a  solution  of  potassium  bichro- 
mate to  which  some  common  salt  has  been  added,  together  with  one- 
fourth  to  three-fourths  of  the  theoretical  amount  of  hydrochloric  or 
sulphuric  acid  necessary  to  liberate  all  the  chromic  acid  (CrOs). 
After  several  hours,  when  the  skin  shows  a  uniform  yellow  color  when 
cut  through  the  thickest  part,  it  is  removed,  the  excess  of  water  pressed 
out  or  drained  away,  and  the  skin  worked  in  a  bath  of  sodium  bisul- 
phite (NaHSO3),  or  thiosulphate,  to  which  has  been  added  some 
mineral  acid  to  liberate  the  sulphur  dioxide :  — 

1)  K2Cr2O7  +  2  HC1  =  2  KC1  +  H2O  +  2  CrO3. 

2)  Na2S203  +  2  HC1  =  2  NaCl  +  H2O  +  S  +  SO2. 

3)  2  CrO3  +  3  SO2  +  3  H2O  =  3  H2SO4  +  Cr2O3. 


LEATHER  581 

The  chromic  acid  is  absorbed  by  the  fibre  and  is  later  reduced  in  situ 
by  the  sulphurous  acid.  It  is  necessary  to  use  a  strong  solution  of 
the  reducing  agent,  so  that  the  reduction  may  be  fully  accomplished 
before  the  chromic  acid  has  time  to  "  bleed  "  from  the  skin.  The 
strength  of  solutions  varies  somewhat  in  the  various  processes,  but  is 
usually  made  from  10  to  30  grams  per  litre  for  the  bichromate,  and 
30  to  50  grams  for  sodium  thiosulphate.  Calculated  on  the  weight 
of  the  skin,  from  4  to  9  per  cent  of  bichromate  and  about  15  per 
cent  thiosulphate  are  usually  employed.  The  amount  of  chromic  acid 
fixed  on  the  fibre  is  about  4  to  6  per  cent,  calculated  as  K2Cr2O7. 

Chrome  leather  is  tough  and  resists  moisture  very  thoroughly. 
On  this  latter  account,  skins  which  are  to  be  dyed  should  be  intro- 
duced into  the  dye  at  once  after  reducing  and  washing,  for  if  allowed 
to  dry,  the  dyeing  is  incomplete.  The  leather  may  be  heated  to  80° 
C.  or  more  without  injury,  and  hence  can  be  dyed  with  some  of  the 
alizarin  colors.  It  is  a  rapid  process,  the  time  of  steeping  in  the 
chrome  bath  being  only  a  few  hours  and  even  less  in  the  reducing 
bath.  It  is  a  light  tannage,  and  on  thick  skins  has  considerable  ten- 
dency to  contract  the  fibre,  and  so  is  not  much  used  for  sole  leather. 
It  is  chiefly  employed  for  glazed  kid,  calf  kid,  and  glove  leathers. 
The  tanned  or  colored  skins  are  oiled  and  stuffed  before  drying. 

Tawing  with  iron  salts  has  been  the  subject  of  several  patents, 
but  these  processes  are  not  used. 

3.  Tanning  with  oils  consists  in  saturating  the  flesh  side  of  split 
skins  with  oils  (whale  or  cod  liver),  and  allowing  them  to  lie  in  heaps 
until  an  oxidation  or  fermentation  of  the  oil  ensues.  The  mass  heats, 
and  a  soft,  spongy  leather,  such  as  chamois  and  buff  leather,  is  formed. 
The  skin  being  limed,  bated,  and  drenched,  excess  of  water  is  removed 
by  pressing,  and  the  skin  is  worked  in  the  stocks  with  oil.  After 
partial  drying,  it  is  again  stocked  with  oil ;  this  is  continued  until  all 
the  moisture  in  the  skin  has  been  replaced  by  oil.  After  partial  oxi- 
dation, the  excess  grease  is  removed  by  pressing,  or  in  the  centrifugal 
machine.  The  thick,  greasy  mass  expressed,  called  "moellen  degras," 
consists  of  semi-oxidized  oil,  and  is  a  valuable  currying  agent.  The 
skins  are  now  washed  in  a  bath  of  soda  or  potash  to  remove  the  rest 
of  the  grease.  These  alkaline  wash-waters  are  treated  with  mineral 
acid,  decomposing  the  soaps,  and  setting  free  the  fatty  acids  which 
rise,  and  are  skimmed  off  as  "  sod-oil,"  also  used  in  currying.  These 
oils  have  undergone  an  oxidation,  probably  with  formation  of  alde- 
hyde-like bodies,  which  unite  with  the  hide  fibre,  similarly  to  the 


582  OUTLINES   OF    INDUSTRIAL   CHEMISTRY 

combination  of  tannic  acid,  and  washing  with  soap  or  alkali  is  not 
sufficient  to  remove  the  combined  fat ;  but  the  uncombined  fat  is 
washed  away  completely. 

The  oil-tanned  skins  are  finally  stretched,  scraped,  and  bleached 
in  the  sun,  or  in  sulphur  dioxide.  Chamois  leather  is  often  further 
softened  by  freezing  while  wet. 

Dilute  alkaline  solutions  of  formaldehyde  will  also  tan  skins ;  the 
product  is  white,  strong  and  soft,  and  is  used  for  gloves. 

Morocco  leather  is  made  from  goat  skins  tanned  with  sumach, 
which  gives  a  light-colored  product.  The  prepared  skins  are  tanned 
by  paddling  in  sumach  liquor;  or  they  are  sewed  up  to  form  bags 
which  are  filled  with  the  liquor,  and  then  piled  in  a  tank  where 
the  pressure  of  one  bag  upon  the  other  forces  the  liquor  through 
the  skins.  The  so-called  French  morocco  is  made  from  sheep  skins, 
either  whole  ("  roans  ")  or  split  ("  skivers  ").  These  leathers  are 
usually  dyed  in  colors,  two  skins  being  placed  with  their  flesh  sides 
together,  and  brushed  over  with  the  color,  or  immersed  in  a  tray  or 
drum  filled  with  the  dye  liquor.  To  imitate  the  grain  of  goat  skin, 
the  skin  is  usually  "  grained  "  by  rolling  under  a  cork-surfaced  board. 

Russia  leather  was  formerly  tanned  with  willow  bark,  but  oak 
bark  is  now  much  used,  especially  for  imitations.  The  peculiar  odor 
is  due  to  an  oil  obtained  by  distilling  birch  bark,  and  used  for  curry- 
ing the  leather.  The  dull  red  color  is  produced  by  dyeing  with  red 
wood  (Brazil  or  saunders-wood) . 

Patent  leather  is  made  by  coating  a  tightly  stretched  split  skin,  or 
"  skiver,"  with  a  varnish  of  linseed  oil,  containing  lampblack,  Prus- 
sian blue,  or  other  pigment.  While  the  leather  is  still  stretched  the 
varnish  is  dried  at  70°  C.,  and  the  surface  is  smoothed  with  fine 
pumice,  and  other  coats  of  varnish  laid  on  and  dried.  The  final  coat 
is  polished  with  tripoli,  or  rotten  stone  and  exposed  to  sunlight  to  de- 
velop a  high  gloss,  possibly  due  to  the  action  of  ultraviolet  rays  on 
the  linseed  oil. 

Parchment  and  vellum  are  made  from  untanned  split  skins.  The 
former  is  made  by  stretching  wet  sheep  skin,  after  liming  and  flesh- 
ing, on  a  frame,  and  drawing  it  smooth  and  free  from  wrinkles. 
Powdered  chalk  is  dusted  over  it,  or  mixed  with  water  and  painted 
on  the  skin  to  absorb  the  grease,  and  the  surface  is  then  smoothed 
by  rubbing  with  pumice.  After  scraping  with  a  steel  blade  and  a 
final  smoothing,  the  skin  is  slowly  dried  in  a  shady  place.  Vellum  is 
made  from  calfskin,  only  those  of  uniform  color  being  used.  The 


LEATHER  583 

liming  lasts  for  three  or  four  weeks,  and  the  washing  is  very  thor- 
ough. The  skin  is  then  split  and  stretched  on  a  frame,  and  dried 
with  scraping  and  pumicing,  as  in  the  case  of  parchment. 

Artificial  leather  is  made  from  various  kinds  of  fibrous  materials, 
usually  cellulose,  coated  with  gelatine  and  heavily  compressed. 
Sometimes  leather  scraps  are  ground  to  shreds,  soaked  in  gum  or 
gelatine,  and  formed  into  boards  by  heavy  pressure.  These  leather- 
ettes are  chiefly  used  for  embossed  trimmings  in  bock  binding,  and 
in  places  where  pliability  is  not  essential. 

Degras  (mo  ell  en)  is  now  so  important  as  a  currying  agent  that 
it  is  manufactured  on  an  extensive  scale.  The  wash  leather  pro- 
duced is  again  saturated  with  oil,  and  the  oxidized  oil  pressed  out ; 
the  process  is  repeated  any  number  of  times,  as  long  as  the  skin  holds 
together. 

The  exact  nature  of  tanning  was  for  long  not  understood,  two 
theories  being  maintained.  The  physical  theory  held  that  the  hide 
fibre  is  merely  coated  with  a  layer  of  the  tan-stuff,  which  prevents 
adhesion  of  the  fibres  on  drying ;  the  chemical  theory  assumed  a  true 
chemical  combination  between  tan-stuff  and  hide  substance.  At  the 
present  time  it  is  generally  thought  that  the  tanning  agent  is  ad- 
sorbed on  the  surface  of  the  fibre.  Only  substances  of  high  molec- 
ular weight,  colloidal  in  their  nature,  are  capable  of  such  adsorption ; 
these  are  the  vegetable  tannins,  chromium  and  aluminum  hydrates 
produced  by  hydrolysis  of  their  salts,  and  aldehydic  condensation 
products  in  the  case  of  oil  and  formaldehyde  tannages. 

REFERENCES 

Grundziige  der  Lederbereitung.     C.  Heinzerling,  Braunschweig,  1882. 

Text-book  of  Tanning.     H.  R.  Procter,  London,  1885. 

Traite  pratique  de  la  Fabrication  des  Cuirs,  etc.     A.  M.  Villon,  Paris,  1889. 

Die  Lohgerberei.     F.  Wiener.     2te  Auf .     Leipzig,  1890. 

Leather  Manufacture.     J.  W.  Stevens,  London,  1891. 

Praktisches  Lehrbuch  der  Lohgerberei.     S.  'Kas,  Weimar,  1891.     (Voigt.) 

Industrie  des  Cuirs  et  des  Peaux.     T.  Jean,  Paris,  1892. 

Cuirs  et  Peaux.     H.  Voinesson  de  Lavelines,  Paris,  1894.     (Bailliere.) 

Die  Herstellung  der  lohgaren  Leder.     L.  Hoffmanns,  Weimar,  1893. 

The  Manufacture  of  Leather.     C.  T.  Davis.     2d  ed.     Philadelphia,  1897. 

The  Art  of  Leather  Manufacture.     A.  Watt.     4th  ed.     London,  1897. 

Die  Chromgerbung.     S.  Hegel,  Berlin.     (Springer.) 

Leather  Industries  Laboratory  Book.     H.  R.  Procter,  London,  1898. 

Leather-Worker's  Manual.     H.  C.  Standage,  London,  1900. 

The  Principles  of  Leather  Manufacture.     H.  R.  Procter,  London,  1903. 


PLASTICS 

Plastics  include  those  solid  materials  capable  of  being  bent, 
modelled  or  molded  into  various  shapes,  and  the  fresh  surfaces  of 
which  coalesce  under  pressure.  These  properties  constitute  plasticity, 
and  in  many  substances  this  may  be  destroyed  by  suitable  treatment 
(p.  31).  The  plastic  condition  may  be  considered  as  to  a  degree  in- 
termediate between  the  solid  and  liquid  states.  Industrially  only 
those  substances  are  important  in  which  plasticity  can  be  decreased 
or  destroyed  by  specific  treatment :  glass,  clays,  resins,  etc.,  may 
properly  be  classed  under  this  head  also. 

CELLULOID 

Celluloid  is  an  artificial  plastic  material  prepared  from  collodion- 
cotton  (p.  479),  camphor,  and  a  suitable  solvent  material,  usually  alco- 
hol. It  has  become  an  important  substitute  for  ivory,  tortoise-shell, 
horn,  bone,  hard-rubber,  and  other  natural  products;  also  it  has 
made  possible  the  production  of  thin,  flexible,  transparent,  or  translu- 
cent films  and  sheets  used  to  a  large  extent  in  place  of  glass.  It 
can  be  readily  cut,  bored,  machined,  and  polished,  and  when  warm 
can  be  pressed  and  bent  into  shapes  which  are  retained  after  cooling. 
It  is  not  attacked  by  water,  oil,  dilute  acids,  or  alkali,  and  is  a  non- 
conductor of  electricity.  Either  natural  or  artificial  camphor  (p.  389) 
may  be  used,  but  must  be  pure  and  free  from  acid  or  chlorine.  The 
collodion-cotton  must  be  free  from  acid,  and  must  dissolve  com- 
pletely; the  presence  of  acid  or  oxidized  cellulose  causes  turbidity 
in  the  finished  product. 

The  collodion,  camphor,  and  alcohol  are  worked  together  in  a 
machine  (having  a  steam-jacketed  pan)  at  a  temperature  of  80°  to 
90°  C.  for  two  to  four  hours,  until  a  tough,  pasty  mass  is  produced. 
The  pan  of  the  machine  is  covered  and  a  pipe  leads  to  a  condenser 
for  recovery  of  the  alcohol  evaporated  during  the  mixing.  The  hot 
mass  is  then  forced  under  heavy  pressure  through  fine  sieves  to  remove 
dirt,  undissolved  fibre,  or  hard  lumps.  The  soft  material  is  then 
worked  from  two  to  four  hours  between  steam-heated  rolls  to  evapo- 
rate the  remainder  of  the  solvent  and  remove  air  bubbles  from  the 
mass.  A  draught  hood  over  the  rolls  leads  the  vapors  to  a  condenser 
for  recovery.  Any  coloring  matter,  such  as  zinc  oxide,  ultramarine, 
lampblack,  etc.,  or  various  coal-tar  colors,  to  be  added  is  often  intro- 

584 


PLASTICS  585 

duced  during  this  final  rolling  process.  By  use  of  calender  rolls,  very 
thin,  evenly  colored  films  are  produced,  which  are  then  arranged  in 
piles  and  heavily  compressed  to  form  blocks,  from  which  sheets  or 
slabs  of  any  desired  thickness  can  be  cut  across  the  ends  of  the 
layers,  thus  giving  the  fine  striated  appearance  of  ivory;  or  with 
thicker  films  of  various  colors,  close  imitation  of  stripe  prints  can  be 
obtained.  Imitation  horn  and  tortoise-shell  are  made  by  rolling  or 
pressing  together  transparent  yellow-colored  blocks,  with  brown  or 
black  pieces,  until  well  amalgamated,  but  not  worked  to  a  uniform 
color. 

Owing  to  the  inflammability  of  celluloid,  its  manufacture  and 
storage  are  subject  to  legislative  control  in  most  countries,  the 
restrictions  imposed  being  similar  to  those  prescribed  for  explosives. 

Substitutes  for  celluloid  which  are  less  inflammable  have  been 
much  desired,  especially  for  photographic  and  theatrical  use ;  of  these 
cellulose  acetate  has  been  much  employed.  Purified  cotton  is  treated 
with  acetic  anhydride,  diluted  with  glacial  acetic  acid,  until  it  dis- 
solves, and  the  solution  then  poured  into  water,  whereby  the  cellulose 
triacetate  is  precipitated.  This  is  soluble  in  chloroform,  acetone,  and 
acetylene  tetrachloride,  is  not  inflammable,  and  is  an  excellent  insu- 
lator for  electrical  use.  Besides  its  use  for  films,  excellent  insulat- 
ing and  protecting  varnish  is  made  from  it  dissolved  in  chloroform, 
or  in  a  mixture  of  alcohol  and  benzine. 

Another  substitute  for  cellulose  is  the  viscose  described  on  p.  490. 


BAKELITE 

Bakelite  is  a  plastic  produced  by  the  condensation  of  phenol  and 
formaldehyde  in  the  presence  of  an  alkaline  condensation  agent. 
Three  forms  of  the  material  are  prepared  as. Bakelite  A,  B,  and  C. 
The  first  product  of  the  condensation  is  the  A-form,  soluble  in  alco- 
hol, acetone,  glycerine,  caustic  soda,  and  other  solvents;  it  is  also 
fusible  at  about  170°  C.,  without  decomposition. 

By  heating,  the  A-form  passes  into  the  B-form,  which  is  solid 
when  cold,  but  plastic  when  hot,  but  swells  in  acetone  and  other 
solvents  without  dissolving.  By  further  heating  this  passes  into  the 
C-form,  which  is  not  fusible  without  decomposition,  does  not  become 
plastic  by  heating,  and  is  insoluble  in  the  various  solvents.  By 
heating  the  material  under  pressure,  the  C-form  is  obtained  without 
formation  of  gas  bubbles,  as  a  hard,  colorless,  or  light  yellow  material. 
It  is  a  non-conductor  of  electricity  and  heat,  and  is  claimed  to  be  a 


586  OUTLINES    OF    INDUSTRIAL   CHEMISTRY 

useful  insulator ;  it  is  not  affected  by  moisture,  dilute  acids,  chlorine, 
or  alkalies.  It  can  be  cut,  turned,  and  machined,  and  is  an  excellent 
substitute  for  ivory,  horn,  amber,  and  similar  articles.  Bakelite  A 
in  solution  forms  an  insoluble  and  brilliant  varnish,  when  applied 
to  wood  or  metal  surfaces;  when  mixed  with  sawdust,  wood-pulp, 
asbestos,  graphite,  powdered  mica,  or  other  filler,  and  the  mass  pressed 
in  moulds  and  heated,  the  plastic  becomes  solid,  and  cements  the 
particles  of  filler  together ;  thus  disks,  handles,  buttons,  and  various 
other  articles  can  be  produced. 

Galalith  is  a  plastic  material  produced  by  the  condensation  of 
formaldehyde  with  casein,  similarly  to  the  formaldehyde  tannage  of 
skins,  p.  582.  Casein  is  separated  from  skimmed  milk  by  coagula- 
tion with  rennet,  and  the  curd,  freed  from  the  whey,  is  carefully  dried 
in  warm  air,  ground,  and  sifted.  The  fine  powder  is  moistened  with 
acetic  acid  and  worked  in  a  mixing  machine  to  form  a  dough,  which 
by  gentle  warming  is  made  plastic  and  is  then  given  the  desired  shape 
by  pressing  in  moulds  and  drying.  The  articles  are  then  cured  by 
long  steeping  in  formaldehyde  solution  followed  by  drying  in  warm 
air. 

CAOUTCHOUC  OR  INDIA  RUBBER 

Caoutchouc  or  India  rubber  is  suspended  in  minute  globules  in 
the  juice  or  latex  of  certain  plants  belonging  to  the  orders  Euphor- 
biacecB,  Apocynaceoe,  and  Artocarpacece,  native  in  nearly  all  tropical 
countries.  There  are  some  60  species  grouped  in  the  5  genera, 
Havea,  Manihot,  Vahea,  Landolphia,  and  Castilloa.  The  finest  grades 
come  from  South  America  (Para)  and  Madagascar.  In  Brazil  the 
trees  are  from  12  to  15  years  old  when  tapped,  and  yield  about  10 
pounds  of  milky  juice,  or  over  3  pounds  of  gum  daily.  Medium  and 
low  grades  are  obtained  from  Central  America,  East  India,  Java, 
Borneo,  and  the  west  coast  of  Africa.  The  plants  in  Africa  are  gen- 
erally vines ;  the  bark  is  partly  stripped  off,  and  the  juice  coagulates 
on  the  vine  by  the  evaporation  of  its  volatile  constituents. 

Jelutong  (or  Pontianak)  from  the  species  Dyera,  indigenous  to 
Malacca  and  Borneo,  and  guayule  from  Parthenium,  a  shrub  indige- 
nous to  the  Chihuahuan  Desert  of  Mexico,  have  furnished  much  low- 
grade  rubber  of  recent  years.  But  as  the  plants  are  destroyed  by 
the  methods  of  collecting  the  latex,  these  materials  will  probably  soon 
cease  to  be  very  important.  Guayule  yields  aKout  9  per  cent  of  the 
weight  of  the  plant  as  crude  rubber. 

Rubber  plants  (chiefly  Havea)  are  now  extensively  cultivated  in 


PLASTICS  587 

Ceylon,  Malacca,  Borneo,  and  other  tropical  countries,  and  the  ex- 
cellent product  (plantation  rubber)  has  become  a  large  factor  in  the 
crude  rubber  market. 

The  milky  white  juice,  which  seems  to  be  distinct  from  the  sap 
of  the  plant,  is  collected  during  July  to  November,  and  coagulated 
by  heating  and  exposing  in  thin  layers  to  wood  smoke,  or  that  of  burn- 
ing palm  nuts  (as  in  Brazil) ;  or  the  latex  is  heated  to  boiling ;  or 
the  juice  of  certain  other  plants  is  added*;  or  dilute  acetic  or 
formic  acid,  salt  solutions,  alum,  phenol,  or  formalin  may  be  used. 
The  rubber  may  also  be  separated  from  the  diluted  juice  in  a  cream 
separator  or  centrifugal. 

Caoutchouc  (CioHie)n  is  a  polymer  of  polyprene  (CioHie),  which 
is  derived  from  isoprene  (CsHs).  Synthetic  rubber^  can  be  prepared 
by  polymerizing  isoprene  (CsHg),  or  by -heating  isoprene  with  dimethyl- 
butadiene  in  the  presence  of  alkali.  The  lower  cost  of  natural  rubber 
would  seem  to  prevent  further  development  in  this  field  at  present. 

Rubber  is  a  highly  plastic  colloid  and  probably  contains  aggre- 
gates in  varying  degrees  of  polymerization ;  the  smaller  molecular 
aggregates  are  soluble  in  carbon  disulphide,  benzene,  and  other  sol- 
vents, but  the  larger,  which  may  combine  with  the  solvent  similarly 
to  the  hydration  of  a  plastic  clay,  are  not  truly  soluble.  These 
swell  in  the  solvent  to  form  membraneous  cells,  which  in  sufficient 
solvent  are  distended  and  ruptured  by  the  osmotic  pressure  of  the 
soluble  part,  thus  decreasing  the  average  size  of  the  aggregates.  This 
decrease  in  polymerization  increases  plasticity  but  decreases  strength. 

Commercial  crude  rubber,  when  freshly  collected,  is  often  nearly 
white,  but  darkens  on  exposure  to  the  air  or  to  smoke,  and  may 
become  almost  black.  Well-prepared  plantation  rubber  is  often  very 
light  in  color.  Lower  grades  of  crude  rubber  often  have  a  foul  odor  due 
to  fermentation  of  albumins  in  the  juice.  Raw  rubber  has  a  specific 
gravity  of  0.915,  is  sticky,  and  freshly  cut  surfaces  unite  firmly ;  it  is 
soft  and  elastic  at  ordinary  temperatures,  but  if  heated  to  about  120° 
C.,  loses  its  elasticity  and  melts  at  150°  C.  It  dissolves  in  carbon 
disulphide  and  chloroform,  and  softens  in  ether,  oil  of  turpentine, 
benzene,  and  naphtha.  Dilute  acids  and  alkalies  have  no  action  on 
it,  but  concentrated  acids  or  free  bromine  or  chlorine  destroy  it. 
Oils  and  grease  also  cause  it  to  become  hard  and  brittle.  The  content 
of  free  resin  (soluble  in  acetone)  may  range  from  1  or  2  per  cent  in 
fine  Para  to  12  or  15  per  cent  in  low  grades  of  rubber. 

The  crude  gum   contains   much   dirt,   sand,   gravel,   bark,   etc., 

*  J.  Soc.  Chem.  Ind.,  1902,  1461.  j  J-  Am.  Chem.  Soc.,  1914,  165. 


588  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

which  is  removed  by  a  washing  process.  It  is  boiled  in  water  until 
softened,  and  ground  between  corrugated  rolls,  which  flatten  the 
lumps  into  thin  sheets  while  a  stream  of  water  plays  over  the  mass, 
washing  away  the  impurities.  Good  Para  rubber  loses  about  15  per 
cent  of  its  weight  during  this  washing,  while  low  grades  shrink  from 
30  to  40  per  cent.  The  rubber  is  then  thoroughly  dried,  hanging 
for  several  weeks  in  well-ventilated  lofts  heated  to  90°  F.  But 
for  most  manufacturing  purposes,  a  pure  gum  is  neither  necessary 
nor  desirable,  and  to  impart  to  it  certain  properties,  it  is  mixed  or 
"  compounded  "  with  various  materials  in  a  "  mixing  mill,"  which 
consists  of  a  pair  of  heavy,  smooth,  hollow,  iron  rollers,  one 
of  which  is  heated  by  steam  to  about  80°  C.  The  materials  added 
are  vulcanizing  agents,  such  as  sulphur,  and  some  metallic  sulphides ; 
certain  sulphides  and  oxides  as  catalytic  agents ;  coloring  pigments, 
fillers,  or  inert  "  make  weights,"  such  as  whiting,  barytes,  lithopone, 
etc.;  rubber  substitutes;  or  coal-tar  pitch.  These  are  thoroughly 
ground  with  the  rubber  to  a  homogeneous  mass,  which  can  then  be 
fashioned  into  any  desired  form  and  finally  vulcanized. 

Unvulcanized  rubber  is  plastic,  is  readily  moulded,  and  clean 
surfaces  unite  if  brought  in  contact  with  each  other.  It  is  on  this 
property  that  the  manufacture  of  soft-rubber  goods  chiefly  depends. 
To  prevent  accidental  adhesion,  fresh  surfaces  are  dusted  with  talc, 
starch,  or  flour,  or  pieces  of  plain  cotton  sheeting  are  interposed. 

Vulcanization  or  curing  is  due  to  a  combination  of  sulphur  with 
the  rubber.  Rubber  unites  with  sulphur  by  chemical  addition  to 
the  double  bonds  of  the  polyprene  molecule,  in  any  proportion  up  to 
30  per  cent ;  but  above  10  to  12  per  cent,  the  product  is  hard  and 
brittle  (ebonite).  The  end  product  of  the  vulcanization  is  probably 
(CioHi6S2)n>  and  the  result  of  this  addition  is  an  increase  in  size  of 
the  aggregates,  due  to  increase  in  the  units,  from  the  polymeriza- 
tion of  which  the  aggregate  is  formed.  This  increase  results  in 
greatly  lessened  plasticity  and  increased  inertness,  hardness,  and 
strength.  Controlling  the  amount  of  sulphur  determines  the  extent 
of  these  changes ;  in  industrial  practice  the  combined  sulphur  varies 
from  about  1  to  2  per  cent  in  soft-rubber  articles  to  20  per  cent,  or 
more,  in  ebonite.  Excess  of  sulphur  over  what  it  is  desired  to 
combine  is  always  added  and  remains  as  amorphous  sulphur  in 
the  product.  The  process  is  facilitated  by  the  presence  of  metallic 
oxides  or  sulphides,  and  is  carried  on  by  dry  heat  at  125°  to  140°  C., 
if  litharge,  zinc  oxide,  or  other  metallic  oxides  are  present  in  the 
compound.  The  goods  (placed  in  a  closed  chamber)  are  heated  by 


PLASTICS  589 

steam,  which  by  this  method  does  not  come  into  contact  with  the 
rubber.  For  soft-rubber  goods  some  8  to  10  per  cent  of  sulphur  is 
added  in  the  compounding  mill,  but  only  a  part  of  it  combines  in  the 
curing,  the  rest  being  merely  disseminated  through  the  mass. 

A  cold  process  of  vulcanizing,  discovered  by  Alexander  Parkes, 
consists  in  immersing  the  rubber  in  a  solution  of  sulphur  chloride 
in  carbon  disulphide.  It  is  used  only  for  small  articles  having  thin 
layers  of  rubber,  since  the  solution  does  not  penetrate  deeply. 

Vulcanizing  destroys  the  adhesive  property  of  rubber,  renders 
it  more  elastic,*  less  soluble,  and  less  susceptible  to  temperature 
changes,  —  it  neither  becomes  sticky  when  moderately  heated,  nor 
brittle  when  cold.  If  antimony  sulphide,  Sb2S5,  is  used  when  vul- 
canizing, the  color  of  the  product  is  red,  owing  to  the  formation  of 
the  trisulphide,  Sb2Ss,  the  remainder  of  the  sulphur  combining  with 
the  rubber. 

Rubber  substitutes  are  extensively  used  in  the  so-called  mechani- 
cal goods,  such  as  bicycle  pedals,  door-mats,  solid  cushions,  and 
springs.  The  best  of  these  is  balata,  obtained  from  the  juice  of 
Mimusops  Kauki,  L.,  a  tree  native  in  Guiana.  This  is  an  inter- 
mediate substance  between  gutta-percha  and  caoutchouc. 

By  mixing  powdered  sulphur  with  raw  linseed  oil  f  and  heating 
in  a  vulcanizer,  a  substance  somewhat  resembling  rubber  is  obtained. 
Or  by  treating  the  oil  with  sulphur  chloride,  a  gummy  mass  of  light 
color  is  produced.  These  "  sulphurized  oils  "  are  largely  mixed  with 
low-grade  rubber  and  with  coal-tar  or  resins,  for  cheap  goods.  Some- 
times they  are  used  without  the  addition  of  any  rubber  whatever. 

Vulcanized  rubber  can  have  its  plasticity  restored  by  the  action 
of  heat,  in  the  presence  of  oils.  Stock  so  treated  is  called  reclaimed, 
recovered,  or  devulcanized  (p.  590)  rubber  and  its  use  for  low- 
grade  articles,  usually  with  the  addition  of  some  new  rubber,  is 
extensive.  In  reclaimed  rubber,  the  uncombined  sulphur  of  the  vul- 
canized stock  is  essentially  all  combined  under  the  action  of  the 
heat  during  the  recovery  process ;  this  increases  the  size  of  the  poly- 
prene  unit  and  thus  tends  to  decrease  plasticity.  The  principal 
change  during  recovery  must  then  be  a  decrease  in  polymerization 
sufficient  to  offset  the  increase  in  combined  sulphur.  According  to 
Weber,  recovered  rubber  always  contains  free  oil,  and  the  solvent 

*  When  unvulcanized  rubber  is  stretched,  it  regains  its  original  form  only  very 
slowly. 

t  Rape  seed  and  castor  oils  are  much  used  abroad  and  corn  oil  in  this  country 
for  these  rubber  substitutes. 


590  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

and  consequent  depolymerizing  action  of  this  oil  at  high  temperatures 
is  the  essential  factor  in  the  process.  Rubber  goods  seldom  contain 
over  15  per  cent  of  total  sulphur,  while  polyprene  can  combine  with 
over  30  per  cent,  so  recovered  rubber  still  has  capacity  to  absorb 
sulphur;  this  decreases  its  plasticity  because  of  the  greater  com- 
plexity of  the  aggregate,  i.e.  recovered  rubber  is  capable  of  revulcan- 
ization.  But  the  product  thus  obtained  will  not  be  identical  with 
ordinary  vulcanized  rubber ;  in  the  complex  (CioHieS^),,,  the  value  of 
x  will  be  greater  and  of  n  less.  Recovered  rubber,  when  re  vulcan- 
ized, gives  a  weaker  and  less  distensible  product. 

The  recovery  process  consists  in  grinding  old  rubber  stock  and  scrap 
to  powder,  removing  the  cloth  or  other  fibre  present,  by  sifting  or 
blowing  with  an  air-blast,  or  by  carbonization  (p.  501)  with  dilute 
sulphuric  acid ;  or  the  acid-carbonized  old  rubber  may  be  boiled  in  an 
8  per  cent  caustic  soda  solution  for  removal  of  the  free  sulphur ;  and 
after  washing  and  drying,  the  product  is  sheeted  in  the  usual  mixing- 
mill.  The  stock  so  treated  may  be  used  directly  as  filler  in  a  batch 
containing  sufficient  new  rubber  to  secure  plasticity ;  or  plasticity 
may  be  restored  after  the  treatment  with  acid  or  caustic,  or  both,  by 
heating  in  the  presence  of  oils  of  various  sorts,  e.g.  rosin  oil.  In  both 
cases  the  stock  is  called  reclaimed  or  recovered  rubber;  the  term 
"  de vulcanized "  should  be  reserved  for  stock  the  plasticity  of  which 
has  been  restored  by  the  oil  treatment. 

The  soda  treatment  is  especially  useful  preceding  devulcanization  ; 
otherwise  during  the  oil  treatment,  the  free  sulphur  in  the  stock  com- 
bines with  the  rubber  and  the  use  of  more  softening  agents  is  necessary, 
giving  a  poorer  product.  Furthermore,  after  free  sulphur  is  removed, 
corn  oil  and  other  similar  oils  can  be  used  in  devulcanization,  which 
will  themselves  "vulcanize"  on  revulcanization  of  the  batch.  This 
leaves  no  free  oil  in  the  final  product,  to  cause  deterioration. 

Vulcanized  rubber  deteriorates  by  keeping,  and  ultimately  be- 
comes hard  and  brittle.  This  apparently  occurs  through  oxidation, 
and  is  influenced  by  the  nature  of  the  compound,  oxidizing  sub- 
stances such  as  lampblack  being  especially  liable  to  spoil  the  rubber. 
Oils,  even  at  ordinary  temperatures,  slowly  attack  rubber,  restoring 
plasticity  by  their  solvent  action,  thus  destroying  strength  and 
promoting  oxidation. 

The  uses  of  rubber  are  exceedingly  numerous,  but  the  largest 
quantities  are  used  for  overshoes,  boots,  rubber  clothing,  automobile 
and  bicycle  tires,  and  hose.  It  may  be  moulded,  as  for  boot  heels, 
solid-rubber  hose,  etc.,  or  made  into  rubber  fabric.  This  latter  is 


PLASTICS  591 

done  by  spreading  a  thin  layer  of  the  un vulcanized  rubber  compound 
on  a  backing  of  cotton  or  woollen  cloth.  The  rubber  may  be  cal- 
endered in  such  a  way  that  it  penetrates  between  the  fibres  ("  fric- 
tion coating  "),  or  it  may  be  simply  applied  to  the  surface  of  the 
cloth  ("  even-motion  coating  ").  Rubber  shoes  and  clothing,  and 
other  fabric  articles  are  entirely  put  together  before  vulcanizing, 
the  seams  being  joined  by  rolling  the  edges  into  contact,  when  they 
adhere.  Such  goods  are  usually  vulcanized  by  heating  at  260°  F. 
for  about  six  hours. 

Rubber  cement  is  made  by  dissolving  a  pure  rubber  in  cold 
naphtha.  A  little  powdered  chalk  is  usually  added. 

Hard  rubber,  vulcanite,  or  ebonite  is  usually  made  from  the 
cheaper  grades  of  rubber,  especially  that  from  Borneo  and  Java, 
and  contains  a  large  amount  of  filling  material.  From  25  to  50  per 
cent  of  sulphur  is  added,  and  the  mass  heated  to  140°  to  150°  C.,  in 
vulcanizing.  It  is  often  shaped  in  the  form  desired  after  it  has  been 
vulcanized. 

GUTTA-PERCHA 

Gutta-percha*  is  obtained  from  the  juice  of  Dichopsis  Gutta, 
Benth.  &  Hook,  a  tree  native  in  the  East  Indies.  The  tree  is  tapped 
in  much  the  same  way  as  for  caoutchouc.  The  crude  material  is 
purified  by  grinding  in  hot  water,  by  which  the  chips,  bark,  sand, 
etc.,  are  removed.  The  plastic  mass  is  then  rolled  into  sheets  or 
formed  into  threads  and  rolled  into  balls  and  pressed.  In  com- 
position it  is  a  terpene  (GioHi6)n,  but  it  also  contains  some  oxy- 
genated resinous  bodies.  Its  texture  is  fibrous,  its  color  varies 
from  white  to  brown,  and  when  free  from  air  its  specific  gravity  is 
slightly  greater  than  1.000.  It  is  tough  and  inelastic  when  cold, 
but  becomes  plastic  at  50°  C.,  and  melts  at  120°  C.  It  is  soluble  in 
carbon  disulphide,  chloroform,  and  warm  benzene.  Alkalies  and 
dilute  acids  have  no  action  on  it,  but  strong  nitric  and  sulphuric 
acids  destroy  it.  By  vulcanizing  with  sulphur,  it  is  rendered  harder 
and  less  plastic  when  heated.  It  is  easily  oxidized  in  the  air  and 
becomes  brittle.  It  is  a  poor  conductor  of  electricity  and  is  better 
than  rubber  for  insulating  purposes,  for  which  it  finds  its  chief  use. 

*  J.  Soc.  Chem.  Ind.,  1897,  815. 


592  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


REFERENCES 

Manufacture  of  India  Rubber  and  Gutta-percha.  Cantor  Lectures  Soc. 
of  Arts.  Thos.  Bolas,  London,  1880. 

Practical  Treatise  on  Caoutchouc  and  Gutta-percha.  R.  Hoffer.  Trans- 
lated by  Wm.  Brannt,  Philadelphia,  1883.  (Baird  &  Co.) 

Die  Fabrikation  der  Kautschuk-  und  Gutta-perchawaaren.  C.  Hein- 
zerling,  Braunschweig,  1883.  (Vieweg.) 

Practical  Treatise  on  the  Raw  Material  and  Manufacture  of  Rubber. 
G.  N.  Nesienson,  New  York,  1890. 

India  Rubber.  Special  Consular  Reports,  Washington,  1892.  (Govern- 
ment Printing  Office.) 

Le  Caoutchouc  et  la  Gutta  Percha.     E.  Chapel,  Paris,  1892. 

Le  Caoutchouc  et  la  Gutta-percha  a  L' Exposition  Universelle  de  1889. 
Rene  Bobet,  Paris,  1893. 

Journal  of  the  Society  of  Chemical  Industry.     1894.     C.  O.  Weber. 

Die  Gutta-percha.     E.  Obach,  Dresden,  1899. 

Crude  Rubber  and  Compounding  Ingredients.  H.  C.  Pearson,  New  York, 
1899. 

Chemistry  of  India-Rubber.     C.  O.  Weber,  Philadelphia,  1902. 


PART   III 
METALLURGY 

METALLURGY  is  the  art  of  extracting  metals  from  their  ores, 
refining  them,  and  separating  them  from  one  another;  it  also 
includes  the  preparation  of  alloys;  sometimes  a  careful  mechanical 
and  heat  treatment  of  the  metals  is  necessary  in  order  to  impart 
desired  qualities.  A  few  metals,  notably  gold,  platinum,  silver, 
copper,  and  bismuth,  are  found  "  native,"  i.e.  in  the  metallic  state 
or  as  alloys ;  but  generally  the  ores  consist  of  oxides,  sulphides,  car- 
bonates, or  other  salts,  more  or  less  impure,  mixed  with  each  other, 
with  gangue  rock  and  earthy  matter. 

Metallurgical  processes  form  two  general  classes,  wet  and  dry ;  the 
former  are  carried  on  in  aqueous  solution,  and  the  latter  involve 
changes  and  reactions  at  high  temperatures. 

Before  attempting  the  separation  of  the  metal  from  its  ore,  cer- 
tain preliminary  operations  ("  ore-dressing  ")  are  generally  necessary 
to  remove  at  least  a  part  of  the  gangue  mechanically,  and  to  bring 
the  valuable  portion  into  proper  condition  for  further  treatment. 
Sizing  and  concentration  are  accomplished  by  hand  picking  ("  cob- 
bing ")  to  separate  large  lumps,  and  by  pulverizing  and  levigating  the 
fine  material.  The  gangue,  being  lighter  specifically  than  the  ore,  is 
carried  off  by  the  water.  The  residue  left  from  this  process  is  called 
the  "  concentrates."  If  magnetic  substances  are  present,  the  ore 
is  often  concentrated  by  allowing  the  pulverized  material  to  fall 
between  the  poles  of  a  magnet,  so  that  the  magnetic  particles  are 
deflected  and  separated  from  the  non-magnetic. 

In  the  wet  metallurgical  processes,  the  metal  is  extracted  by  some 
form  of  leaching,  generally  after  preliminary  treatment,  to  get  the 
metal  into  the  form  of  a  soluble  salt.  This  preliminary  treatment 
varies  much,  and  will  be  considered  in  connection  with  each  special 
case. 

In  the  dry  processes,  the  ore  is  usually  calcined  or  roasted  and 
then  reduced  in  another  furnace.     This  reduction  generally  consists 
in  exposing  the  ore  to  the  action  of  carbon  and  carbon  monoxide  at 
2q  593 


594  OUTLINES   OP    INDUSTRIAL   CHEMISTRY 

high  temperatures,  or  sulphur  may  be  relied  upon  to  take  oxygen 
from  the  oxides  in  the  prepared  ore.  The  gangue  substances  are 
rendered  fluid  by  adding  fluxes  which  fuse  to  liquid  slag  with  them. 
Commonly  the  flux  is  silica  (SiO2)  where  acid  conditions  are  desired ; 
for  basic,  lime  is  used. 

The  crude  metal  obtained  by  any  reduction  process  generally  re- 
quires "refining,"  to  remove  the  impurities  left  in  it.  The  methods 
for  this  refining  will  be  considered  in  connection  with  the  individual 
metals. 

ROASTING 

Roasting  consists  in  producing  chemical  changes  at  a  temperature 
which,  though  quite  high,  is  not  sufficient  to  cause  fusion.  No 
metallurgical  operation  is  more  important,  for  the  results  of  various 
processes  depend  on  converting  the  ore  into  a  suitable  chemical  con- 
dition by  roasting.  For  example,  in  the  chlorination  of  gold  ores, 
sulphur  and  arsenic  must  first  be  completely  removed ;  or,  to  reduce 
zinc  from  sulphide,  the  latter  must  first  be  converted  into  oxide. 

An  oxidizing  roast  serves  to  remove  sulphur,  arsenic,  etc.,  by  con- 
version to  SO 2,  As2O3,  etc.,  which  are  carried  away  by  the  draft. 

PbS  +  3  O  =  PbO  +  SO2. 

A  sulphatizing  roast  converts  sulphides  to  sulphates,  usually  with 
the  object  of  leaving  some  metal  in  a  soluble  condition.  This  is 
accomplished  by  keeping  the  temperature  somewhat  lower,  and  the 
depth  of  the  ore  bed  greater,  than  for  an  oxidizing  roast,  and  reduc- 
ing the  draft.  These  conditions  favor  the  maximum  production  of 
SOa  from  the  sulphur  in  the  ore,  and  prevent  it  being  carried  into  the 
stack  before  it  can  combine  with  the  metallic  oxides. 

When  it  is  necessary  to  remove  all  of  the  sulphur,  arsenic,  etc., 
from  an  ore,  any  sulphates,  arsenates,  etc.,  that  have  formed  are 
reduced  by  stirring  in  fine  coal  with  the  ore  and  excluding  the  air  as 
much  as  possible.  The  resulting  sulphides  are  then  given  a  further 
oxidizing  roast. '  When  the  sulphur,  arsenic,  etc.,  are  practically  all 
removed,  the  ore  is  said  to  be  dead  roasted,  or  sweet  roasted. 

A  chloridizing  roast  converts  metals  into  chlorides  by  means  of 
the  interaction  of  atmospheric  oxygen  and  common  salt  with  the 
sulphides,  arsenides,  etc.  In  the  most  important  case  of  chloridiz- 
ing, that  of  silver,  the  sulphide  is  first  oxidized  to  sulphate,  and  then 
the  following  reaction  takes  place  :  — 

Ag2SO4  -f  2  NaCl  =  2  AgCl  -.+  NaaSO4.      • 


METALLURGY 


595 


Roasting  of  fine  ores  is  more  common  than  of  lump.  Fines  are 
heated  in  beds  only  a  few  inches  deep,  so  that  they  do  not  pack  and 
prevent  their  proper  exposure  to  the  air.  They  are  turned  over  and 
over  to  expose  new  surfaces.  Coarse  ores  worked  in  this  way  can 
receive  only  a  superficial  roast  in  any  reasonable  time,  and  are  there- 
fore roasted  in  large  heaps  5  or  6  feet  deep. 

Figure  123  shows  a  reverberatory  furnace  that  has  been  used  to 
prepare  ores  for  the  lead  blast-furnace.  (C)  is  the  fire-box.  The  ore 
is  charged  through  the  hole  (D)  in  lots  of  about  two  tons,  and  is  grad- 
ually turned  over  and  worked  along  the  hearth  (A)  by  means  of 
hand  rabbles  inserted  through  the  side  doors.  The  purpose  of  the 
stepped  hearth  is  to  bring  the  ore  nearer  the  roof  at  the  flue  end, 


FIG.  123. 

and  thus  get  more  benefit  of  what  heat  remains  in  the  gases.  A  rather 
better  construction  omits  the  steps  and  gives  the  hearth  a  gentle 
uniform  slope  from  the  flue  toward  the  fire.  When  the  ore  reaches 
the  lower  end  of  the  hearth  (A),  the  sulphur  is  mostly  burned  off.  The 
charge  is  then  dropped  to  the  hearth  (B),  where  it  is  slagged  or  par- 
tially fused.  This  is  possible  because  the  heat  comes  directly  from 
the  fire-box  and  is  confined  in  a  narrower  space  than  in  the  long  hearth. 
The  purpose  of  this  fusing  is  to  prevent  the  fine  ore  being  carried  away 
by  the  strong  draft  when  put  into  the  blast-furnace  later.  It  also 
removes  more  sulphur  by  the  reaction,  - 

2  PbSO4  -f  SiO2  =  Pb2SiO4  +  2  SO2  +  O2. 

The  "slag  hearth  is  now  seldom  used  because-  the  high  temperature 
increases  the  metal  losses  in  the  fume.  Instead,  the  ore  is  moder- 
ately sintered  at  the  bridge  end  of  the  roasting  hearth. 

This  same  style  of  furnace  with  no  slagging  hearth  is  used  to 
roast  gold-bearing  pyrite  (FeS2)  previous  to  chlorination ;  also  blende 
(ZnS).  There  are  usually  doors  on  both  sides  of  the  furnace,  and 
the  hearth  is  not  over  15  feet  wide.  To  lessen  the  labor  in  moving 
the  ore,  the  hearth  for  blende  roasting  is  not  over  7  or  8  feet  wide 


596 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


with  doors  on  only  one  side,  to  prevent  excessive  admission  of  cold 
air ;  blende  is  specially  difficult  to  roast  if  the  proper  temperature  is 
not  maintained.  For  galena  or  blende,  the  length  of  hearth  is  about 
40  feet ;  but  it  may  be  65  feet  for  pyrite,  which  generates  a  good 
deal  of  heat  in  roasting,  and  hence  is  less  dependent  on  the  heat  from 
the  fireplace. 

In  recent  years  mechanical  furnaces  have,  to  a  considerable 
extent,  though  by  no  means  wholly,  supplanted  hand-operated  fur- 
naces. These  are  cheaper  and  permit  better  regulation  of  the  air 
supply  and  uniformity  of  operation.  They  are  not  well  adapted  to 
roasting  galena  ores,  because  the  latter  become  so  sticky  at  a  moder- 
ate temperature  that  they  cannot  be  efficiently  handled  by  mechani- 
cal means.  The  Ropp  furnace  (Fig.  124)  may  be  taken  as  typical  of 


FIG.  124. 

a  class  that  has  been  used  with  much  success  for  roasting  pyrite  and 
blende.  Ore  is  supplied  regularly  by  the  automatic  feeders  (M),  is 
moved  along  the  hearth  (A)  by  the  rakes  (R),  and  is  discharged  at 
the  farther  end.  The  rakes  are  carried  by  trucks  (E)  running  on 
a  narrow  track.  The  trucks  are  propelled  by  a  wire  rope  which  passes 
around  the  sheaves  (I)  and  (I'),  power  being  applied  through  the 
latter.  When  the  rakes  enter  the  furnace,  cold  air  is  kept  out  by  means 
of  the  doors  (L)  and  (L/),  which  are  hinged  at  the  top  and  form  a 
sort  of  air  lock,  (L)  closing  before  the  rake  pushes  (L')  open.  The 
device  is  used  at  the  discharge  end  of  the  hearth,  as  shown  by  (K) 
and  (K').  Heat  is  supplied  from  the  fireplaces  (N),  and  the  gases 
pass  to  the  flue  (0).  The  rakes  are  exposed  to  the  air  outside  the 


METALLURGY 


597 


furnace  longer  than  to  the  heat  and  fumes  of  the  furnace.     This 
prolongs  their  life. 

The  McDougal  furnace  (Fig.  125  *)  is  circular  in  horizontal  sec- 
tion and  so  has  less  wall  surface  in  proportion  to  the  hearth  area  than 
any  other  shape;  thus  there  is  less  radiation  of  heat.  Further,  the 
large  amount  of  brick  in  the  several  hearths  absorbs  much  heat  from 
one  hearth  and  transmits  it 
to  the  ore  lying  on  the  next 
above.  The  furnace  is  largely 
used  for  roasting  copper  ores 
that  contain  a  good  deal  of 
pyrite,  and  for  ordinary  pyrite 
in  the  manufacture  of  sul- 
phuric acid.  This  mineral 
generates  so  much  heat  in 
roasting  that  no  other  fuel  is 
required.  The  furnace  is  also 
coming  into  use  for  ores  that 
are  not  self-roasting,  one  or 
more  auxiliary  fireplaces  being 
attached  in  this  case.  It  has 
a  considerably  greater  diam- 
eter (14  ft.  6  in.)  than  most 
designs  of  the  McDougal  type, 
and  this  large  size  presented 
a  special  difficulty  owing  to 
the  distortion  of  the  stirring 
arms  and  the  vertical  shaft 
when  heated.  The  trouble 
was  avoided  by  water  cool- 
ing. Water  is  delivered  from 
the  pipe  (B)  extending  to  the 
bottom  of  the  hollow  vertical  shaft,  and,  in  passing  upward,  is  directed 
to  the  end  of  each  rabble  arm  and  back  to  the  shaft  by  means  of  a 
baffle,  and  finally  discharges  through  the  pipe  (C)  into  a  stationary 
annular  cup,  from  which  it  runs  away.  The  principal  wear  is  on  the 
stirring  blades,  and  these  are  easily  detached  from  the  horizontal 
arms. 

In  starting,  a  wood  fire  is  kept  on  the  bottom  hearth  till  enough 
heat  is  stored  in  the  brickwork  to  ignite  the  ore;   the  fire  is  drawn, 
*  Eng.  and  Min.  Journal,  76,  123. 


FIG.  125. 


598  OUTLINES   OF    INDUSTRIAL   CHEMISTRY 

the  shaft  and  stirring  arms  set  in  motion  by  the  gearing  beneath  the 
furnace,  and  the  ore  is  delivered  to  the  top  hearth  by  an  automatic 
feeder  in  the  hopper  (A).  The  stirring  .blades  on  one  hearth  turn 
the  ore  over  and  gradually  move  it  to  the  centre,  where  it  drops  to 
the  next  lower  hearth.  On  this  the  ore  travels  to  the  circumference, 
in  which-  there  are  two  discharge  holes.  A  receiving  hopper  (E)  is 
placed  beneath  the  lowest  hearth.  The  air  for  oxidation  admitted 
through  doors  on  the  bottom  hearth  passes  upward  by  the  same 
openings  through  which  the  ore  falls,  discharging  by  the  pipe  (D)  to 
the  main  flue.  The  strong  draft  at  the  holes  connecting  the  different 
hearths  carries  considerable  fine  ore  into  the  flue;  to  prevent  this, 
the  ore  may  be  discharged  from  one  hearth  to  another  through  a  tube 
independently  of  the  air  passage.* 

The  diameter  of  the  old  McDougal-type  furnace  was  limited  by  the 
allowable  length  of  the  arms.  Even  when  water-cooled,  they  sag  at  the 
ends  because  they  are  supported  only  at  the  centre  of  the  furnace.  By 
using  a  large  central  driving  shaft  (4  feet  in  diameter)  and  the  same 
length  of  arms,  the  area  of  the  annular  hearth  is  greatly  increased.  Fur- 
naces 22  feet  in  diameter  are  now  constructed.  The  weight  of  the  central 
shaft  and  rabble  arms  is  carried  on  roller  bearers  at  the  bottom. 


WHITE-HOWELL  ROASTING   FURNACE 

FIG.  126. 

The  Howell-White  furnace  (Fig.  126),  resembling  the  Oxland 
calciner,  considerably  used  to  roast  gold  and  silver  ores,  is  a  brick- 
lined  iron  cylinder,  set  on  friction  rollers  at  a  gentle  angle  to  the  hori- 
zontal. It  is  about  25  feet  long  and  4  or  5  feet  in  diameter.  Heat 
comes  from  a  stationary  furnace  at  the  lower  end,  and  ore  is  auto- 
matically fed  at  the  upper  end.  The  revolution  of  the  cylinder  turns 
the  ore  over  and  over  and  makes  it  travel  to  the  discharge  end,  where 

*  U.  S.  Patents,  729170,  May  26,  1903,  and  740589,  Oct.  6,  1903. 


METALLURGY 


599 


FIG.  127. 


it  falls  into  a  hopper.  The  oxidizing  action  is  increased  by  blades 
along  the  sides,  which  lift  the  ore  and  let  it  fall  in  a  shower.  The  draft 
carries  out  a  good  deal  of  fine  dust  as  it  falls  from  the  feed  hopper  into 
the  furnace,  and  also  as  it  drops  from  the  blades,  making  a  dust  cham- 
ber necessary.  The  dust  can  be  much  lessened  by  feeding  the  ore 
through  a  Rumsey  diaphragm,  in  which  the  opening  for  the  discharge 
of  gases  is  contracted  and  the  ore  is  fed  through  a  bent  pipe  on  to  the 
bottom  of  the  cylinder  out  of  the  draft. 

Figure  127  *  shows  a  shaft  furnace  that  is  used  to  calcine  coarse 
zinc  ores  for  the  expulsion  of  CC>2  and  H^O.  The  ore,  charged  at 
(A),  passes  downward  and  is  drawn  off  at  (B), 
being  heated,  in  its  descent,  by  the  gases  from 
the  fire  grates  (C). 

To  roast  lump  ore  in  a  heap,  the  ground 
is  made  smooth  and  firm,  with  a  little  slope  to 
drain  water  off  to  the  sides  in  case  of  rain. 
Two  layers  of  cord  wood,  or  more  if  necessary, 
are  placed  regularly  on  this  ground  to  cover 
a  slightly  greater  area  than  is  planned  for  the 
heap  (say  25  feet  wide  and  40  feet  long,  or  more). 
In  the  bottom  layer  of  wood  are  left  several 
spaces  6  inches  wide,  extending  from  the  sides  to  the  centre,  serving 
as  flues  to  start  the  ignition  of  the  heap.  These  flues  are  loosely 
filled  with  small  sticks,  and  connect  with  wooden  chimneys  along  the 
centre  line  of  the  pile.  Ore  from  1  to  3  inches  in  diameter  is  piled 
on  the  wood  to  a  depth  of  about  5  feet ;  the  top  and  sides  are  covered 
several  inches  deep  with  pieces  as  small  as  J  inch,  and  a  last  layer 
of  fines  is  placed  over  this,  to  prevent  rapid  combustion  that  would 
fuse  the  ore  and  thus  stop  the  roasting.  The  fire  started  in  the  small 
flues  gradually  spreads  and  ignites  the  ore,  which  may  burn  for  two 
or  three  months,  the  air  entering  at  the  base  of  the  heap  and  escap- 
ing through  small  cracks  in  the  surface.  Care  is  used  that  these 
cracks  do  not  become  so  large  as  to  cause  excessive  draft.  Part  of 
the  ore  is  not  properly  roasted,  and  goes  into  a  subsequent  heap. 
If  the  ore  does  not  contain  enough  sulphur  to  maintain  the  roast,  a 
certain  amount  of  coal  or  small  wood  is  mixed  in  the  pile  when  first 
made. 

The  heaps  emit  the  disagreeable  sulphur  fumes  near  the  ground, 
and  require  a  long  time  to  do  the  work.     These  disadvantages  are 
overcome  by  the  use  of  cubical  stalls  (300  or  400  cubic  feet)  placed 
*  After  Ingalls,  Metallurgy  of  Zinc  and  Cadmium.     New  York,  1903. 


600 


OUTLINES   OF   INDUSTRlA   CHEMISTRY 


side  by  side ;  they  are  enclosed  by  substantial  brick  walls,  and  con- 
nected to  a  high  chimney  by  a  common  flue.  The  operation  of  stalls 
is  similar  to  that  of  heaps. 

Dwight-Lloyd  Sintering  Machine.  —  This  machine  (Fig.  128)  is 
extensively  used  for  sintering  (agglomerating  or  partially  slagging) 
or  rough  roasting  ores  and  for  removing  volatile  matter.  Its  essen- 
tial feature  is  a  series  of  pallets  that  are  pushed  into  contact  like  the 
pans  of  a  pan  conveyor,  but  which  are  not  attached  to  each  other. 
Each  pallet  is  30  inches  wide  and  18  inches  long,  and  has  a  perforated 


Fia.  128. 

bottom,  planed  to  make  a  tight  joint  when  pushed  over  the  suction- 
box.  At  other  points  in  its  circuit,  it  is  supported  by  four  wheels 
that  roll  on  guides.  Each  pallet  is  successively  pushed  under  the  feed 
hopper,  receives  a  layer  (usually  4  inches)  of  charge,  then  goes  under 
the  ignition  box  in  which  a  coal,  gas,  or  oil  flame  playing  down  on  the 
top  ignites  the  charge.  Continuing  over  the  suction-box,  combus- 
tion, induced  by  the  down  draft,  progresses  downward  through  the 
material  so  that  roasting  and  agglomeration  are  completed  when  the 
pallet  discharges  its  cake  into  a  car  or  hopper  at  the  end.  It  is  evi- 
dent that  unless  there  is  sufficient  sulphur  in  the  charge  to  furnish 
heat,  coal  or  other  combustible  material  must  be  added.  The  ton- 
nage treated  will  vary  from  30  to  75  tons  in  24  hours  according  to  the 
charge  and  the  completeness  of  the  roasting. 


IRON  AND  STEEL 

The  ores  of  iron  are  red  hematite  (Fe2O3),  brown  hematite  —  the 
limonite  of  the  mineralogist  —  (2  Fe2O3  •  3  H2O),  magnetite  (Fe3O4), 
and  siderite  (FeCOs),  these  minerals  being  mixed  with  more  or  less 
silica,  clay,  etc.,  besides  containing  small  percentages  of  manganese, 
phosphorus,  and  sulphur. 

The  crude  iron  is  made  in  large  blast  furnaces  (Fig.  129  *),  which 
are  circular  in  horizontal  section,  and  are  lined  with  refractory  fire- 
brick. The  ore,  together  with  coke  and  lime- 
stone, is  raised  to  the  top  of  the  furnace  by  a 
hoist  (A)  and  discharged  into  the  hopper  (B). 
By  lowering  the  bell  (C)  the  materials  fall  into  the 
hopper  (D),  from  which  they  are  dropped 
into  the  furnace  by  lowering  the  bell  (E). 
The  object  of  the  two  bells  and  hoppers  is 
to  prevent  the  escape  of  large  volumes  of 
gas  from  the  top  of  the  furnace. 

Immense  volumes  of  air,  heated 
to  600  or  800°  C.,  are  blown  through 
a  set  of  tuyeres  (F),  near  the  bottom 
of  the  furnace,  at 
a  pressure  of  12  to 
15  pounds  per 
square  inch. 

In  a  blast  fur- 
nace, there  are 
two  currents  pass- 
ing in  opposite 
directions.  A 
rapid  gas  current, 
heated  to  nearly 
1600°  C.,  just  -- 

Al_  ~^W  FIG.  129. 

above  the  tuyeres, 

rises  through  the  slowly  descending  solid  charge  to  the  throat  (top), 
and  escapes  into  a  large  pipe  (J),  the  "  downcomer."  In  ascending, 
it  cools  to  200-300°  C.,  and  acts  chemically  on  the  charge. 


*  After  Campbell,  The  Manufacture  of  Iron  and  Steel.     New  York,  1903. 

601 


602  OUTLINES    OF   INDUSTRIAL   CHEMISTRY 

Following  the  descending  column  of  ore,  flux,  and  coke,  four 
zones  of  reactions  can  be  distinguished  :  — 

(1)  Zone  of  Preparatory  Heating  (100-300°  C.),  at  the  top  of  the 
furnace,  in  which  all  the  moisture  and  much  of  the  combined  water 
are  given  up  to  the  gas  current  and  heat  is  absorbed  from  it. 

(2)  Upper   Zone  of   Reduction  (300-900°  C.).      (a).  CO  present 
in  the  gas  acts  on  the  ore  according  to  the  exothermic  reactions :  — 

3  Fe203  +  CO  =  2  Fe3O4  +  CO2  (begins  at  200°  C.). 
Fe3O4  +  CO  =  3  FeO  +  CO2  (begins  above  450°  </.). 
FeO    +  CO  =  Fe  +  CO2  (begins  at  about  700°  C.). 

The  CO2  resulting  from  these  reactions  joins  the  gas  current  and  heats 
it,  while  the  spongy  iron  continues  its  descent.  These  reactions  are 
reversible  unless  the  CO2  is  diluted  with  CO,  and  they  are  never  com- 
plete in  the  furnace. 

(b)  The  CO2  content  of  the  gas  is  also  increased  by  a  partial  de- 
composition of  CO  in  the  presence  of  the  heated  charge  which  acts  as 
a  catalyzer  between  250  and  600°  C.  in  the  reversible  reaction :  — 

2  CO  =  C02  +  C. 

(c)  A  third  source  of  CO2  in  this  zone,  lower  down  at  about  800°  C., 
is  the  lime-rock  flux  (and  siderite,  if  present).     Much  of  this  is,  how- 
ever, reduced  to  CO  by  the  coke. 

(3)  Lower  Zone  of   Reduction   (900-1200°  C).     Here,   the  char- 
acteristic reaction  is :  — 

FeO  +  C  =  Fe  +  CO. 

Small  amounts  of  Mn,  Si,  and  P  are  also  reduced  from  their  oxides 
by  the  solid  carbon  which  continues  its  action  into  the  lower  part  of 
the  furnace. 

(4)  Zone  of  Fusion  (1200-1600°  C.).     This  zone  is  filled  with  glow- 
ing  coke,  through  which   the   melting  charge   trickles   down.     The 
molten  iron  becomes  saturated  with  carbon,  and  dissolves  all  the 
metals  reduced  from  the  ore  together  with  any  free  S  or  P.     The  silica 
and  alumina  (clay)  of  the  gangue,  combining  with  the  lime  of  the  flux, 
fuse  to  a  slag  (waste  product),  which  collects  above  the  molten  iron 
in  the  space  below  the  tuyeres,  called  the  crucible. 

The  slag,  being  specifically  lighter  than  the  metal,  rises  to  the  top, 
and  is  tapped  out  through  the  cinder  notch  (G)  at  intervals  of  about 
2  hours.  Every  4  to  6  hours,  the  iron  is  drawn  off  through  the  metal 
tap  (H).  The  slag  notch  is  stopped  with  a  metal  plate  that  chills 


IRON   AND   STEEL  603 

the  slag  and  closes  the  opening.  The  metal  tap  is  closed  by  ramming 
in  a  clay  plug.  The  slag  may  be  either  run  into  ladles  (holding  sev- 
eral tons)  and  hauled  to  a  dump,  or  granulated  by  pouring  into  water 
and  sluiced  away.  Granulated  slag  is  often  dried,  ground,  and  made 
into  slag  cement.  Typical  slags  run  30-35  per  cent  SiC>2,  10-15  per 
cent  A12O3,  and  50-55  per  cent  CaO. 

The  iron  is  run  into  "  sows  "  (moulds)  and  cast  into  pigs  before 
shipping,  or,  if  the  iron  is  made  into  steel  near  by,  it  is  tapped  into 
ladles  and  sent  molten  to  the  steel  plant. 

Up  to  about  90  feet,  increasing  the  height  of  an  iron  blast  furnace 
saves  fuel,  since  the  deep  charge  absorbs  more  of  the  heat  of  the  gas. 
Higher  furnaces  have  been  built,  but  have  not  proved  so  efficient,  and 
it  is  doubtful  if  a  height  of  90  or  100  feet  will  again  be  exceeded.  A 
furnace  12  to  14  feet  in  diameter  and  90  feet  high  commonly  produces 
500  to  600  tons  of  pig  iron  in  24  hours.  This  involves  the  charging 
of  1500  to  2000  tons  of  ore,  fuel,  and  flux. 

The  shape  of  the  furnace  walls  has  a  marked  effect  on  the  capac- 
ity. A  gentle  increase  in  diameter  from  the  throat  down  to  the  fusion 
zone  allows  for  expansion  of  the  charge  as  it  heats  up  and  prevents 
"  hanging  "  of  the  charge  followed  by  "  slips  "  (falls)  that  interfere 
with  the  working  of  the  furnace  and  cause  explosions.  The  fusion 
zone  narrows  down  rapidly  to  the  tuyere  level  to  provide  for  the 
contraction  of  the  charge  when  melted.  This  section  is  called  the 
bosh.  The  walls  are  cooled  with  water-blocks  to  protect  them  from 
the  effects  of  heat  and  chemical  action. 

The  gas  from  the  top  of  the  furnace  usually  contains  over  20  per 
cent  CO  by  volume,  and  has  about  one-half  the  heating  value  of  the 
coke.  A  part  of  it  is  used  for  pre-heating  the  blast  and  the  remainder 
is  available  for  generating  power  either  by  burning  it  directly  under 
boilers  or,  more  recently,  directly  in  internal  combusion  engines. 
When  the  latter  are  used,  careful  washing  is  necessary  to  remove 
dust  that  would  clog  the  ports  of  the  engines.  One  large  American 
plant  develops  40,000  H.P.  from  its  gas  engines.  Thirty  per  cent 
of  the  calorific  power  of  the  gas  may  be  utilized  in  gas  engines  as 
against  a  maximum  of  about  15  per  cent  in  steam  engines. 

The  air-blast  is  heated  by  passing  it  through  "  stoves,"  which  are 
large  cylindrical  structures  filled  with  checkerwork  of  fire-brick,  and 
thoroughly  pre-heated  by  burning  in  them  some  of  the  gas  from  the 
top  of  the  furnace.  There  are  usually  three  or  four  stoves  for  one 
blast-furnace,  the  blast  passing  through  one  while  the  others  are 
heating. 


604  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

Moisture  in  the  air  greatly  reduces  the  capacity,  and  its  variations 
interfere  with  the  smoothness  of  operation  of  a  blast  furnace.  This 
is  owing  to  the  heat  absorbed  in  the  fusion  zone  by  the  reaction, 
C  +  H2O  -^  CO  +  H2  (see  p.  40).  The  gases  produced  are  effective 
reducing  agents  in  the  upper  zones,  but  are  not  needed,  as  the  reduc- 
tion capacity  of  the  furnace  is  much  greater  than  the  fusion  capacity. 
The  latter  alone  limits  the  output.  The  moisture  is  removed  from 
the  air  before  going  to  the  stoves,  in  the  Gayley  dry-blast  by  artificial 
refrigeration.  Trays  of  calcium  chloride  have  also  been  used,  the 
calcium  chloride  being  regenerated  by  evaporation  of  the  absorbed 
moisture  by  a  blast  of  hot  gas. 

Pig  iron  is  the  metal  produced  in  the  blast  furnace.  Its  composi- 
tion varies  according  to  the  character  of  the  ore  and  the  operation  of 
the  furnace.  The  composition  of  the  slag,  percentage  of  the  fuel, 
and  regulation  of  the  blast  determine  the  quantities  of  Si,  C,  S,  and 
Mn  in  the  iron.  The  iron  may  take  up  3  or  4  per  cent  of  C,  somewhat 
less  than  3  per  cent  each  of  Mn  and  Si,  and  the  greater  part  of  the 
P  and  S  in  the  original  ore.  Carbon  and  silicon  are  the  most  impor- 
tant elements  taken  up  by  the  iron,  as  the  hardness,  strength,  and 
other  properties  vary  with  their  percentages.  Phosphorus  makes 
the  metal  brittle  when  cold,  but  a  small  amount  is  desirable  in  making 
intricate  castings,  as  it  increases  the  fluidity  and  causes  the  metal  to 
fill  all  £arts  of  the  mould.  Sulphur  makes  the  iron  (or  steel)  "  red 
short  "  or  brittle  at  high  temperatures. 

In  chemical  composition  cast  iron  is  identical  with  pig  iron;  it 
usually  contains  over  2.2  per  cent  of  carbon,  and  is  either  gray  or 
white,  depending  on  whether  the  carbon  is  separated  out  as  flakes 
of  graphite  (slow  cooling)  or  is  in  the  form  of  carbide  (chilled). 
Mottled  iron  is  a  mixture  of  the  two.  Cast  iron  is  not  malleable  at 
any  temperature. 

Steel  is  iron  that  is  malleable  at  some  temperature  and,  in  addi- 
tion, is  (1)  either  cast  into  an  initially  malleable  mass  (mild  steel)  or 
(2)  may  be  hardened  by  sudden  cooling.  The  carbon  content  varies 
from  practically  zero  in  soft  steels  (that  cannot  be  hardened)  up  to 
2.2  per  cent.  Ordinary  steels  contain  from  0.75  to  1.5  per  cent  carbon, 
the  hardness  increasing  with  the  carbon  content.  Mild  steels  with 
less  than  0.2  per  cent  carbon  cannot  be  hardened,  and  are  distinguished 
from  wrought  iron  of  similar  composition  only  by  the  manner  of 
manufacture. 

Wrought-iron  is  usually  made  from  pig  (though  considerable 
scrap-iron  is  utilized)  by  burning  out  the  carbon,  silicon,  manganese, 


IRON   AND   STEEL 


605 


phosphorus,  and  sulphur  as  far  as  possible,  in  reverberatory  furnaces 
lined  with  hematite  or  magnetite.  The  oxidation  of  these  elements 
is  effected  partly  by  atmospheric  oxygen,  but  also  by  the  iron  oxide 
of  the  furnace  lining.  The  pig-iron  may  contain  6  per  cent  or  more  of 
these  elements,  but  they  amount  to  less  than  1  per  cent  in  the  finished 
product.  The  metal  becomes  less  fusible  as  they  are  removed,  and 
finally  it  is  in  a  pasty  state,  so  that  the  slag  cannot  be  completely 
separated.  The  iron  is  gathered  into  large  balls  and  the  slag  partly 
removed  by  working  in  a  mechanical  squeezer  or  under  a  steam  ham- 
mer. It  still  may  contain  as  much  as  2  per  cent  of  slag,  which  gives 
the  metal  its  special  quality  of  welding  readily,  and  largely  prevents 
the  tendency  to  crystallize,  due  to  the  small  quantity  of  phosphorus 
and  sulphur  present.  However,  the  slag  decreases  the  tenacity  by 
preventing  the  complete  union  of  the  particles  of  the  iron. 

While  soft  steel  has  largely  displaced  wrought-iron,  the  latter  is 
still  demanded  by  blacksmiths  and  machinists  for  certain  purposes. 

Steel  is  made  from  iron  by  four  different  methods :   the  Bessemer 
process  is  the  cheapest  and  produces  the  largest  quantity ;    the  open 


FIG.  130. 

hearth  is  next  and  its  product  is  generally  considered  more  reliable 
for  structural  work  that  is  subject  to  frequent  shocks ;  the  crucible 
and  the  cementation  processes  produce  only  small  quantities,  sup- 
plying the  demand  for  fine  tools,  watch-springs,  needles,  etc. 

The  Bessemer  process  is  conducted  in  a  "  converter,"  shown  un- 
mounted in  Fig.  130.*  It  is  supported  by  and  revolves  on  the  trun- 
nions (A),  (B),  being  turned  by  a  pinion  fastened  on  (B),  which 

*  After  Campbell,  The  Manufacture  of  Iron  and  Steel.     New  York,  1903. 


606  OUTLINES   OF   INDUSTRIAL.  CHEMISTRY 

meshes  with  a  rack  moved  by  a  hydraulic  piston.  The  converter  is 
lined  with  refractory  material,  and  as  the  bottom  lining  wears  away 
much  faster  than  the  side  the  entire  bottom  is  made  removable, 
being  held  in  position  by  clamps,  so  that  it  may  be  quickly  replaced 
by  a  new  one,  which  has  been  previously  prepared  and  heated. 

In  operation  the  converter  is  turned  to  a  horizontal  position,  and 
molten  pig-iron  poured  in.  An  air-blast,  with  a  pressure  of  20  to  30 
pounds  per  square  inch,  is  turned  on,  entering  through  the  trunnion 
(A),  pipe  (C),  wind-box  (D),  and  tuyeres  (E),  and  the  converter  is 
turned  to  a  vertical  position.  The  air  passing  through  the  metal  in 
many  fine  jets  first  oxidizes  the  manganese  and  silicon,  thus  gener- 
ating enough  heat  to  greatly  increase  the  temperature  of  the  charge. 
When  the  silicon  has  been  largely  removed  the  carbon  begins  to 
burn;  and  even  with  a  charge  of  18  tons,  in  less  than  15  minutes 
after  the  blast  is  turned  on,  almost  the  whole  of  the  manganese, 
silicon,  and  carbon  have  been  oxidized,  the  last  passing  off  as  CO, 
which  burns  at  the  mouth  of  the  vessel  to  CO2,  while  the  others  com- 
bine with  a  certain  amount  of  oxidized  iron  to  form  slag.  Above  a 
certain  temperature,  carbon  has  a  greater  affinity  than  silicon  for 
oxygen,  and  will  burn  first ;  but  in  American  practice  it  is  customary 
to  add  some  cold  scrap-iron  to  the  charge  to  keep  the  temperature 
below  this  critical  point.  Another  method  of  lowering  the  tempera- 
ture is  to  introduce  steam  with  the  air-blast ;  the  decomposition  of 
this  steam  absorbs  a  large  amount  of  heat.  After  the  carbon  has 
practically  all  burned  out  (shown  by  the  dropping  of  the  flame  at 
the  converter  mouth),  the  converter  is  turned  down  and  hot  lumps  of 
ferromanganese  or  melted  spiegeleisen  added  to  supply  the  proper 
percentages  of  manganese  and  carbon ;  then  the  metal  is  poured  into 
a  ladle  from  which  the  ingot  moulds  are  filled.  The  manganese  makes 
the  metal  work  well  in  the  subsequent  rolling,  and  also  combines 
with  the  dissolved  oxygen,  lessening  the  blow-holes  in  the  solid  ingot ; 
while  the  carbon  imparts  the  proper  degree  of  hardness,  strength, 
etc. 

Spiegeleisen  is  pig-iron  containing  4  or  5  per  cent  of  carbon  and 
5  to  20  per  cent  manganese ;  ferromanganese  is  pig  with  6  or  7  per 
cent  carbon  and  25  to  85  per  cent  manganese.  A  considerable  weight 
of  the  former  is  used  to  produce  hard  (high  carbon)  steel,  while  a 
small  amount  of  the  latter  yields  soft  (low  carbon)  steel. 

In  the  United  States  the  acid  process  is  employed  in  making 
Bessemer  steel,  and  as  neither  phosphorus  nor  sulphur  is  removed, 
only  iron  low  in  these  substances  is  used.  The  converter  is  lined 


IRON   AND    STEEL  607 

with  silicious  sandstone,  and  as  there  is  not  enough  base  to  combine 
with  any  P2O5  which  may  form,  this  is  at  once  reduced  by  the  iron, 
the  phosphorus  passing  into  the  steel. 

In  the  basic  process  the  converter  lining  is  calcined  dolomite  or 
limestone  (cemented  by  tar),  and  the  slag  is  so  basic  that  the  P2O5  is 
strongly  held  by  the  CaO.  To  lessen  corrosion  of  the  lining,  lumps 
of  quicklime  are  added  with  the  charge.  The  silicon  in  the  pig-iron 
charged  is  kept  lower  than  in  the  acid  process  to  make  the  slag  as 
basic  as  possible  by  keeping  out  silica.  In  the  basic  process  much 
of  the  heat  is  due  to  the  oxidation  of  phosphorus  (of  which  the 
pig  must  contain  nearly  2  per  cent  in  order  to  supply  enough  heat), 
while  in  the  acid  process  it  is  mainly  due  to  burning  the  silicon. 
Sulphur  is  removed  with  the  phosphorus ;  but  if  the  sulphur  is  high, 
the  blow  may  have  to  be  continued  after  the  phosphorus  is  sufficiently 
removed.  There  is  almost  no  flame  during  the  burning  of  the  phos- 
phorus and  sulphur.  Therefore,  small  sample  ingots  are  cast  from  a 
hand  ladle,  and  the  condition  of  the  charge  is  determined  by  the  appear- 
ance of  the  fracture  of  the  chilled  ingot.  The  process  is  completed 
by  the  addition  of  spiegeleisen  as  in  the  acid  process.  The  slags  are 
so  rich  in  phosphorus  that  they  are  valuable  for  fertilizer  (p.  171). 

The  basic  process  is  more  expensive  than  the  acid  and  is  not  used 
in  the  United  States  because  we  have  an  abundance  of  ores  low  in 
phosphorus.  In  this  country,  phosphorus  is  aiever  allowed  to  be 
over  0.1  per  cent  in  the  steel,  and  must  often  be  less.  Germany  is 
the  chief  user  of  the  basic  process. 

In  some  plants,  the  iron  for  the  converter  is  remelted  in  cupolas, 
which  in  a  general  way  resemble  a  blast-furnace,  though  much  smaller ; 
but  at  large  plants  producing  their  own  iron  near  at  hand  the  metal 
comes  direct  from  the  blast-furnace  still  molten.  It  is  stored  in  large 
covered  "  mixers,"  or  reservoirs,  in  which  oil  or  gas  is  burned,  if  neces- 
sary, to  prevent  the  surface  chilling.  These  "  mixers  "  equalize  the 
composition  of  the  different  charges  of  iron,  thus  permitting  the  uni- 
form operation  of  the  converters. 

In  the  open-hearth  process,  pig-iron,  scrap  steel,  and  iron  ore  are 
melted  in  a  regenerative,  reverberatory  furnace.  Without  the  regen- 
erative principle  (p.  43)  a  sufficient  temperature  cannot  be  main- 
tained  to  keep  the  charge  properly  fused  after  the  impurities  are 
oxidized.-  In  this  country  the  usual  practice,  when  using  a  silicious 
hearth,  is  to  first  charge  the  scrap  and  put  the  pig-iron  on  this,  so  that, 
in  melting,  the  silicon,  manganese,  and  carbon  of  the  pig  having, 
greater  affinity  for  oxygen,  oxidize  first,  protecting  the  iron  of  the  pig 


608 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


and  scrap  from  oxidation.  Any  oxidized  iron  will  form  slag  on 
coming  into  contact  with  silica.  Silicon  and  manganese  are  largely 
burned  by  the  air  entering  from  the  regenerative  chambers,  and  the 
carbon  is  oxidized  by  reaction  with  iron  ore,  still  assisted  by  the  air. 
The  process  is  sometimes  conducted  with  the  omission  of  either  the 
scrap  or  the  iron  ore. 

With  an  acid  (silicious)  hearth,  phosphorus  and  sulphur  are  not  re- 
moved, because  they  are  retained  by  the  iron  instead  of  entering  an 
acid  slag.  With  a  basic  lining  (usually  burned  dolomite),  and  the 
addition  of  burned  lime  with  the  iron  ore,  the  basic  slag  formed  has 
so  strong  an  affinity  for  phosphoric  acid  that  the  iron  does  not  reduce 
the  latter.  Consequently,  the  phosphorus  is  largely  removed,  as 
is  also  the  sulphur.  The  proper  amounts  of  carbon  and  manganese 
are  restored  to  the  metal  by  the  use  of  ferromanganese. 

Figure  131  *  shows,  on  the  left,  a  half-longitudinal  section  through 
a  Campbell  furnace,  and  on  the  right  a  half-longitudinal  elevation 


FIG.  131. 

with  a  section  through  the  two  regenerative  chambers  on  that  side ; 
two  similar  regenerators  on  the  other  side  connect  the  air  and  gas 
tunnels  (a)  and  (b).  To  avoid  excessive  oxidation  of  the  metal, 
the  air  enters  the  furnace  at  (a'),  above  the  gas  which  goes  in  at  (V) ; 
proper  mixture  is  obtained  by  having  the  two  streams  enter  at  slightly 
different  angles. 

The  Campbell  furnace  has  loose  connection  with  gas  and  air 
ports,  and  rests  on  several  sets  of  heavy  steel  rollers  (c),  so  that  it 
can  be  tilted  about  its  longitudinal  axis  for  quickly  pouring  the  prod- 
uct when  it  has  reached  the  proper  composition.  This  saves  con- 
siderable time;  and  in  cases  where  the  composition  must  be  kept 
within  narrow  limits  the  quick  pouring  is  of  special  advantage. 

*  After  Campbell,  The  Manufacture  of  Iron  and  Steel.     New  York,  1903. 


IRON   AND   STEEL  609 

An  important  difference  between  the  basic  open  hearth  and  the 
basic  Bessemer  process  is  that,  in  the  former,  iron  with  any  percentage 
of  phosphorus  can  be  used,  while  in  the  latter  the  phosphorus  content 
must  be  nearly  2  per  cent,  and  is  often  about  3  per  cent.  The  reason 
for  this  difference  is  that  the  basic  Bessemer  converter  depends 
chiefly  on  the  rapid  oxidation  of  phosphorus  to  maintain  the  proper 
temperature,  while  in  the  open-hearth  process  the  temperature  is 
maintained  by  carbonaceous  fuel.  A  basic  Bessemer  blow  is  com- 
pleted in  20  minutes  or  less ;  but  in  the  open-hearth  process  it  takes 
6  to  12  hours  to  finish  a  charge,  depending  on  the  size  and  style  of 
furnace,  the  composition  of  the  stock  used,  etc.  Several  modifica- 
tions of  the  ordinary  procedure  have  been  devised  to  save  time,  one 
of  which,  the  Monell  process,  is  being  considerably  adopted  in  this 
country.  In  this,  iron  ore  and  burned  lime  are  first  heated  in  the 
furnace,  and  iron,  still  molten  from  the  blast-furnace,  but  moder- 
ately cool,  is  then  poured  in.  Most  of  the  phosphorus  and  some  of 
the  carbon  are  quite  rapidly  oxidized ;  the  former  combining  with 
the  lime,  the  latter  escaping  as  gas,  which  puffs  up  the  phosphoric 
slag  and  causes  most  of  it  to  run  out  of  the  furnace ;  but  this  raising 
of  the  slag  is  much  less  violent  than  if  the  ore  and  lime  were  not  first 
heated.  An  advantage  of  this  process  is  that  the  phosphorus  is 
chiefly  removed  at  an  early  stage  (while  at  a  high  temperature  it 
would  go  off  less  rapidly  than  the  carbon) ;  and  therefore  the  steel 
can  be  poured  as  soon  as  the  carbon  is  reduced  to  the  right  point. 

The  crucible  process,  as  commonly  practised  in  the  United  States, 
consists  in  melting  the  best  grade  of  wrought-iron  with  charcoal  in 
either  graphite  or  clay  crucibles,  the  molten  iron  absorbing  the  proper 
amount  of  carbon  from  the  charcoal.  The  usual  weight  of  the  charge 
is  80  pounds  or  less,  and  the  melt  lasts  3  or  4  hours.  Sometimes 
a  little  manganese  oxide  is  added,  as  the  manganese  reduced  by  the 
charcoal  renders  the  steel  more  forgeable.  In  Sweden,  pig-iron  is 
melted  with  iron  ore,  the  latter  oxidizing  the  excess  of  carbon.  When 
the  melting  is  thoroughly  under  way,  a  certain  amount  of  silicon  is 
reduced  from  the  SiC>2  in  the  crucible.  Part  of  this  silicon  combines 
with  the  iron,  and  part  unites  with  any  dissolved  oxygen,  and  thus 
decreases  the  blow-holes  that  would  remain  in  the  metal  after  casting. 

In  the  cementation  process,  bars  of  wrought-iron  are  embedded  in 
charcoal,  in  long  covered  chests  of  fire-brick,  and  kept  at  a  yellow 
heat  for  a  week  or  more.  Carbon  is  slowly  absorbed  by  the  iron, 
the  slag  in  the  latter  remaining  in  the  steel.  This  slag  may  be  removed 
from  the  steel  by  melting  in  crucibles,  thus  improving  the  quality, 


610  OUTLINES   OF    INDUSTRIAL   CHEMISTRY 

but  increasing  the  cost.  Since  the  process  lasts  two  or  three  weeks, 
including  the  time  necessary  to  heat  the  furnace  and  cool  it  after- 
ward, the  method  is  too  expensive,  and  has  been  largely  superseded 
by  the  ordinary  crucible  process. 

Special  Steels.  —  Manganese,  chromium,  nickel,  tungsten,  molyb- 
denum, etc.,  are  used  to  produce  special  steels  noted  for  their  hard- 
ness, toughness,  resistance  to  shock,  strength,  etc.  Small  quantities 
of  manganese  are  added  to  ordinary  steel  to  lessen  blow-holes  and 
make  the  metal  work  well  when  rolled  or  forged.  Increase  of  man- 
ganese above  1.5  per  cent  and  up  to  6  or  8  per  cent  makes  the  steel 
brittle,  but  at  the  latter  point  the  character  entirely  changes,  and  the 
product  combines  extreme  hardness  with  unusual  toughness.  Chro- 
mium also  imparts  great  hardness.  Tungsten  and  molybdenum  are 
used  to  make  self-hardening  steel,  so-called  because  tools  made  from 
it  do  not  need  to  be  heated  and  quenched  to  make  a  hard  cutting  edge. 
This  edge  is  retained  much  longer  than  with  ordinary  steel. 

Manganese,  chrome,  and  nickel  steels  are  frequently  used  for  such 
purposes  as  burglar-proof  safes,  armor  plate,  and  machine  parts  sub- 
ject to  excessive  wear  and  shock.  Nickel  steel  has  been  used  for 
several  of  the  largest  engine  shafts  ever  made. 

Electrical  methods  of  making  iron  and  steel  have  advanced  so  far 
that  they  are  producing  in  commercial  quantities,  but  do  not  yet 
really  compete  with  the  common  methods.  The  products  are  claimed, 
however,  to  be  of  exceptional  quality.  In  most  of  the  furnaces  the 
charge  is  heated  by  the  electric  arc,  coke  being  used  for  reduction 
and  carburization  as  in  the  ordinary  blast-furnace.  In  some  cases  the 
heat  is  produced  by  an  induction  current,  the  material  in  the  furnace 
taking  the  place  of  the  secondary  coil  of  a  transformer. 


COPPER 

The  chief  sources  of  copper  are  sulphide  ores,  the  most  important 
being  chalcocite  (Cu2S),  bornite  (Cu3FeS3),  and  chalcopyrite  (CuFeS2). 
These  minerals  are  almost  invariably  associated  with  large  quantities 
of  pyrite  (FeS2) ;  and  in  some  cases,  notably  the  Spanish  copper  mines, 
the  yield  is  principally  cupriferous  pyrite.  Oxides  and  carbonates  are 
common  in  the  upper  zones  of  copper  deposits,  but  are  of  much  less 
importance  than  the  sulphides.  Native  copper  (i.e.  copper  occurring 
in  the  metallic  state  in  nature)  is  found  in  a  number  of  places,  but  not 
in  commercial  quantities  except  in  the  famous  Lake  Superior  mines 
in  Michigan. 

The  common  method  of  copper  extraction  is  to  smelt  the  ore  to 
produce  a  slag,  which  is  thrown  away,  and  a  matte,  i.e.  a  mixture 
of  copper  and  other  heavy  metals  as  sulphides,  which  is  further 
treated  to  remove  iron  and  sulphur,  and  leave  the  copper  in  the  me- 
tallic state.  Fine  ore  is  treated  in  reverberatory  furnaces,  and  coarse 
in  blast-furnaces. 

Reverberatory  smelting  of  copper  ores  is  done  in  furnaces  which 
somewhat  resemble  a  simple,  hand-roasting  furnace;  but  with  a 
horizontal  instead  of  sloping  hearth,  to  prevent  the  molten  charge 
running  to  one  end  (see  Fig.  14).  The  roof  slopes  downward  from 
the  fire-bridge  toward  the  flue,  to  bring  the  gases  closer  to  the  material 
on  the  hearth  as  they  become  cooler,  and  thereby  get  more  benefit 
of  their  heat.  The  width  also  gradually  decreases  toward  the  flue 
end,  so  that  the  material  there  is  kept  hot  enough  in  the  corners  of 
the  furnace. 

The  heat  required  for  smelting  is  usually  generated  by  burning 
bituminous  coal  in  a  fire-box  and  using  an  induced  draught.  With 
long  flame  coals  the  hearth  may  be  between  80  and  100  feet  long.  By 
using  oil,  gas,  or  powdered  coal  in  specially  designed  burners,  the  length 
of  hearth  may  be  increased  up  to  120  feet.  The  width  is  seldom  greater 
than  20  feet,  as  this  is  about  the  maximum  distance  allowable  for  work- 
ing a  charge  from  the  side  doors.  Charges  of  400  tons  may  be  smelted 
in  24  hours  in  the  largest  furnaces. 

The  charge  is  dropped  through  holes  in  the  roof  near  the  fire- 
bridge where  the  heat  is  greatest.  Silicious  ore  is  also  occasionally 
fed  along  the  sides  of  the  furnace  near  the  walls,  to  cool  and  protect 
them  from  chemical  action  (ore-fettling). 

611 


612  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

The  material  commonly  treated  in  a  reverberatory  furnace  is  the 
finer  portion  (seldom  as  coarse  as  half-inch  particles)  resulting  from 
the  mechanical  concentration  of  the  ore.  As  this  is  very  likely  to 
contain  over  30  per  cent  sulphur  and  25  per  cent  iron,  with  only  5  to 
10  per  cent  copper,  its  direct  fusion  would  produce  a  matte  too  low 
in  copper.  It  is,  therefore,  roasted  till  the  sulphur  is  reduced  to  8 
or  10  per  cent,  and  then  should  go  directly  to  the  smelting  furnace 
with  as  little  cooling  as  possible,  to  save  fuel. 

Any  Fe2Os  produced  in  roasting  is  reduced  by  reaction  with  some 
of  the  remaining  sulphide  — 

+  FeS  =  7  FeO  +  SO2. 


The  FeO  and  any  CaO,  A^Os,  etc.,  combine  with  the  SiC>2  to  form 
slag,  while  the  remaining  iron  and  sulphur  unite  with  the  copper  to 
form  matte,  which  also  takes  up  whatever  gold  and  silver  there  is 
in  the  charge.  The  copper  in  the  matte  varies  from  35  to  50  per  cent, 
depending  on  the  ore.  The  slag  rises  while  the  matte  sinks,  their 
respective  specific  gravities  being  about  3.5  and  5.  As  the  separa- 
tion is  not  perfect,  the  slag  contains  approximately  \  per  cent  copper. 

The  composition  of  the  slag  varies  considerably  with  the  ore. 
Uncombined  silica  is  often  present  and  is  apt  to  contain  copper,  thus 
increasing  the  loss.  It  is  better  to  add  enough  limestone  to  slag 
this  silica,  and  form  a  more  fluid  slag  that  retains  less  matte.  The 
best  practice  is  to  add  the  limestone  before  the  ore  goes  to  the  roast- 
ing furnace,  because  it  gets  thoroughly  mixed  in  the  latter  and  there- 
fore causes  quicker  smelting. 

The  slag  is  skimmed  through  a  door  at  the  end  of  the  furnace 
opposite  the  fire-box,  and  the  matte  is  tapped  through  a  hole  in  the 
furnace  side  which  is  closed  by  a  clay  plug,  and  is  opened  by  driv- 
ing in  a  pointed  steel  bar.  Usually,  the  slag  from  several  charges  is 
skimmed  before  any  matte  is  tapped  ;  and,  except  for  special  reasons, 
the  matte  and  slag  are  never  completely  removed.  By  keeping  a 
large  body  of  molten  material  on  the  hearth,  an  extra  reservoir  of 
heat  is  provided  to  quickly  melt  a  new  charge,  and  the  latter  is  pre- 
vented from  seriously  sticking  to  the  bottom. 

The  matte  is  carried  in  large  ladles,  holding  several  tons,  directly 
to  the  converters  (p.  615),  or  is  cast  in  moulds  and  cooled  if  the  plant 
is  not  arranged  for  direct  conversion.  If  the  contour  of  the  ground 
permits,  the  best  way  to  get  rid  of  the  slag  is  to  run  it  into  a  large 
stream  of  water  when  available.  This  suddenly  chills  and  granulates 
it,  and  carries  it  away  to  the  dump.  Before  falling  into  the  water  the 


COPPER  613 

slag  runs  through  a  large  cast-iron  pot,  so  that  any  matte,  accidentally 
run  out  of  the  furnace  with  it,  may  have  a  chance  to  settle.  When 
skimming  is  finished,  the  upper  part  of  the  liquid  slag  in  this  pot  is  either 
poured  or  tapped  out,  but  the  rest  is  resmelted.  If  granulation  cannot 
be  used,  the  slag  is  carried  to  the  dump  in  large  cast-iron  pots  or  cars. 

As  the  temperature  of  the  gases  escaping  from  the  furnace  will 
average  from  1200°  to  1400°  C.,  it  is  well  to  utilize  them  in  a  steam 
boiler,  which  may  easily  reduce  them  to  350°  C.  Care  must  be  used, 
however,  that  the  boiler  is  so  arranged  as  not  to  injure  the  draught 
of  the  furnace,  for  this  would  reduce  the  smelting  capacity,  which  is  the 
first  consideration. 

Blast-furnace  Smelting.  —  A  blast-furnace  for  copper  must  be 
much  lower  than  for  iron,  to  avoid  the  strongly  reducing  conditions 
that  would  precipitate  metallic  iron.  The  depth  of  charge  is  only 
8  to  12  feet  above  the  tuyeres,  and  the  width  must  be  much  less  than 
in  an  iron  furnace,  for  the  strong  blast  needed  to  penetrate  the  charge 
in  a  wide  furnace  would  blow  too  much  material  out  of  the  top. 
Widths  at  the  tuyere  level  vary  from  35  to  56  inches ;  but  with  the 
circular  form  these  would  give  too  little  capacity,  so  the  furnaces  are 
made  rectangular.  In  most  plants,  the  furnaces  are  between  15  and 
21  feet  long  and  treat  400  to  600  tons  in  24  hours.  One  furnace  in 
Montana  is  87  feet  long  and  treats  2500  tons  of  charge  every  24  hours. 
By  shutting  off  the  blast  from  a  section  of  this  furnace,  it  is  possible  to 
make  repairs  without  seriously  interfering  with  the  operation  of  the 
main  portion,  so  there  seems  to  be  no  limit  to  the  length,  provided  the 
conditions  of  ore  supply  warrant  such  large  capacities.  The  walls 
are  of  steel  or  iron,  water-jacketed  to  prevent  their  fusion.  Brick 
walls,  formerly  in  common  use,  still  survive  in  some  places,  but  are 
liable  to  be  partially  eaten  away  by  the  slag,  and  the  half-fused  ore 
forms  accretions  on  them.  When  these  are  barred  off,  the  walls  are 
apt  to  be  more  or  less  broken.  Neither  of  these  troubles  can  occur 
in  the  case  of  a  water-jacket. 

The  fuel  is  coke,  introduced  alternately  with  the  ore  and  flux 
through  charging  doors  on  both  sides.  Air  is  blown  in  through  the 
tuyeres,  under  a  pressure  of  about  2  pounds  per  square  inch.  A  few 
ores  are  self-fluxing,  but  usually  it  is  necessary  to  add  either  limestone 
or  quartz  to  form  an  easily  fusible  slag.  Considerable  variation  is 
allowable  in  the  composition  of  the  slag,  but  if  it  gets  much  over  40 
per  cent  SiC>2,  it  will  not  flow  well  nor  allow  a  good  separation  of  matte 
without  the  use  of  excessive  fuel.  The  quantity  of  coke  used  in  com- 
mon practice  varies  from  8  to  14  per  cent  of  the  total  weight  of  ore  and 


614  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

flux,  depending  on  the  ease  with  which  the  charge  fuses,  the  quality 
of  the  coke,  volume  and  pressure  of  the  air-blast,  the  detail  shape  of 
the  furnace,  and  the  depth  of  the  charge  above  the  tuyeres.  Consider- 
able of  the  sulphur  in  the  ore  may  be  burned,  and  the  heat  thus  gen- 
erated, with  that  of  the  oxidation  of  the  iron  of  the  pyrite,  decreases 
the  quantity  of  coke  required.  Some  sulphur  is  also  volatilized  with- 
out burning,  since  one  atom  of  sulphur  is  quite  readily  distilled  from 
pyrite,  FeS2,  leaving  FeS.  Frequently  two-thirds  of  the  sulphur  in  the 
ore  is  either  burned  or  volatilized.  The  vigorous  oxidizing  conditions 
produced  in  the  blast-furnace  make  it  commonly  unnecessary  to  give 
the  ore  the  preliminary  roast  that  is  usual  in  reverberatory  practice. 
However,  when  there  is  a  large  per  cent  of  sulphur  and  very  little 
copper,  preliminary  roasting  may  be  advisable,  lest  the  resulting  matte 
be  of  too  low  grade  to  handle  economically.  A  number  of  large  scale 
experiments  have  been  made  with  a  view  to  smelting  without  a  pre- 
liminary roast,  or  the  use  of  coke,  and  the  process  has  been  perfected 
in  one  or  two  places  where  the  right  kind  of  ores  are  at  hand.  A  large 
percentage  of  iron  pyrite  is  necessary  to  supply  sufficient  heat  (but 
such  ores  are  generally  low  in  copper),  and  unusually  large  quantities 
of  air  must  be  blown  in.  At  Mt.  Lyell,  Tasmania,  as  much  as  80  or 
90  per  cent  of  the  sulphur  is  thus  removed,  yielding  a  high-grade  matte 
from  low-grade  ore  in  one  operation.  Usually  the  first  operation  under 
this  method  yields  matte  too  low  in  copper  for  the  converters,  and  this 
is  smelted  again  to  raise  the  grade.  At  Mt.  Lyell  only  J  per  cent  of 
coke  is  used,  this  being  fed  along  the  sides  to  lessen  the  chilling  of  slag 
by  the  air-blast  and  consequent  stopping  of  tuyeres. 

If  there  is  any  FesOs  in  the  material  charged  to  the  furnace,  it  is 
reduced  to  FeO  either  by  reaction  with  sulphide  according  to  the 
equation  given  on  p.  612,  or  by  means  of  CO  from  the  combustion  of 

FesQ,  +  CO  =  2  FeO  +  CO2. 

The  various  elements  unite  to  form  the  slag  and  matte  the  same  as 
in  the  reverberatory,  but  it  is  not  possible  to  "  float  "  uncombined 
silica  in  the  blast  furnace,  as  may  be  done  in  the  reverberatory,  since 
a  pasty  slag  cannot  be  made. 

There  is  but  little  space  below  the  tuyeres  to  collect  the  molten 
products,  so  these  run  out  together  into  a  large  forehearth,  or  settler. 
The  spout  from  the  furnace  is  arranged  with  an  inverted  dam  that 
dips  below  the  surface  of  the  slag,  and  thus  prevents  any  air  from  the 
tuyeres  escaping  at  this  point.  For  large  furnaces,  the  settler  just 
mentioned  is  a  circular  basin,  15  feet  in  diameter  and  4  feet  deep  inside, 


COPPER  615 

made  of  fire-brick.  While  this  is  filling  up  when  the  furnace  is  first 
put  in  blast,  the  matte  and  slag  separate  according  to  their  specific 
gravities,  and  the  surface  of  the  slag  chills,  thus  making  an  effective 
cover.  The  slag  flows  out  continuously  from  the  full  settler,  through 
a  spout  at  the  top  and  on  the  side  opposite  the  furnace.  The  matte  is 
tapped  periodically  from  a  hole  in  the  side,  near  the  bottom.  Both 
products  are  disposed  of  in  the  same  way  as  in  reverberatory  smelting. 

Comparison  of  Reverberatory  and  Blast-furnaces.  —  The  chief 
difference  between  these  two  is  that  the  former  is  best  suited  for  fine, 
and  the  latter  for  coarse,  ore.  Coarse  ore  in  the  reverberatory  would 
smelt  very  slowly,  because  the  total  surface  for  a  unit  weight  is  com- 
paratively so  small  that  the  bases  (iron,  lime,  etc.)  cannot  come  in 
intimate  contact  with  the  acid  (silica).  This  difficulty  is  compensated 
in  the  blast-furnace  because  the  very  high  temperature  right  at  the 
point  of  combustion  is  applied  immediately  to  the  ore.  Consequently, 
where  the  silica  and  bases  do  come  in  contact,  there  is  a  rapid  reaction 
and  fusion,  and  fresh  surfaces  are  quickly  exposed.  On  the  other  hand, 
any  large  proportion  of  fine  ore  is  not  permissible  in  the  blast-furnace 
because  some  of  it  would  be  carried  out  by  the  blast,  and  the  rest  would 
so  choke  the  furnace  as  to  cause  reducing  conditions  sufficient  to  pre- 
cipitate metallic  iron,  which,  however,  would  not  be  really  melted  and 
would  therefore  form  "  sows,"  and  these  would  gradually  fill  up  the 
furnace  and  put  it  out  of  commission.  Reverberatory  smelting  is 
now  on  the  increase,  largely  because  recent  improvements  in  ore- 
dressing  and  mining  methods  have  made  available  large  bodies  of  low- 
grade  copper  ore  which  yield  fine  concentrates. 

Copper-converting.  —  The  matte,  either  directly  from  one  of  the 
processes  just  described,  or  (occasionally)  after  remelting  in  a  special 
blast-furnace,  is  blown  in  a  converter  resembling  that  used  in  the 
Bessemer  steel  process.  The  chief  difference  is  that  the  tuyeres  are 
in  the  side  several  inches  above  the  bottom,  yet  below  the  surface  of 
the  charge.  The  object  of  this  is  to  keep  the  air  from  passing  through 
and  chilling  the  metallic  copper  that  results  from  the  operation.  A 
modern  design  resembles  a  barrel  resting  on  its  side  upon  rollers,  with 
a  row  of  tuyeres  along  one  side  and  an  opening  above  for  charging 
and  discharging  and  for  the  escape  of  the  gases.  The  advantage 
of  this  shape  is  that,  for  a  given  capacity,  the  charge  is  not  so 
deep  as  in  the  upright  form,  and  a  lower  blast  pressure  can  be  used, 
with  less  cost  for  blowing  and  less  loss  of  solid  material  blown  out  of  the 
converter.  The  converter  lining  is  ground  quartz  or  silicious  ore,  with 
just  enough  plastic  clay  to  hold  it  together. 


616  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

The  chemistry  of  the  process  is  very  different  from  that  of  a  steel 
converter.  The  elements  to  be  removed  from  the  matte,  aside  from 
small  amounts  of  zinc,  arsenic,  etc.,  are  nearly  25  per  cent  of  sulphur 
and  25  to  40  per  cent  of  iron,  instead  of  say  6  per  cent  of  carbon,  silicon, 
etc.,  as  in  the  conversion  of  iron  into  steel.  The  sulphur  passes  off 
as  SO2,  while  the  iron  oxide  combines  with  silica  from  the  lining  to 
form  slag,  which,  when  all  the  iron  is  thus  removed,  is  poured  off,  and 
the  blow  continued  till  the  last  of  the  sulphur  is  oxidized,  leaving  the 
metallic  copper.  The  finishing  reaction  after  all  the  iron  is  removed  is  : 

Cu2S  +  2  Cu2O  =  6  Cu  +  SO2. 

A  lining  must  be  repaired  on  the  average  after  3  to  6  charges,  instead 
of  lasting  for  thousands  of  charges,  as  in  acid  steel  converters.  The 
time  required  to  finish  a  10-ton  charge  is  about  2  hours,  while  a  steel  con- 
verter of  the  same  capacity  will  be  ready  for  a  second  charge  in  about 
15  minutes  after  receiving  the  first.  Converter  slag  carries  Ij  to  2j 
per  cent  copper,  and  is  returned  to  the  blast-furnace  or  reverberatory. 

The  necessity  of  frequent  relining  of  the  converters  with  silica,  and 
the  heavy  cost,  have  led  to  the  adoption  of  inert  basic  linings.  These 
are  usually  made  of  magnesite  brick,  and  may  be  further  protected 
by  a  coating  of  fused  magnetite.  Greater  economies  in  labor,  power, 
air,  and  repairs  are  possible ;  and  larger  charges  can  be  handled  in  the 
same  sized  shell,  since  the  acid  lining  must  be  very  thick.  The  chief 
advantage  of  the  basic  converter  is  that  2500  tons  or  more  of  copper 
can  be  converted  without  relining,  as  compared  with  10  tons  when  an 
acid  lining  is  used.  The  chemical  reactions  in  both  converters  are  the 
same,  the  difference  being  that  silica  is  derived,  in  one  case  from  the 
lining,  and  in  the  other  from  silicious  ore  or  quartz  charged  at  intervals 
into  the  mouth.  Basic  converters  are  rapidly  displacing  acid  con- 
verters in  all  the  large  smelters. 

Copper-leaching  Processes.  —  Large  quantities  of  Spanish  pyrite, 
containing  3  per  cent  or  less  copper,  are  piled  in  immense  heaps  as 
much  as  30  feet  high,  wet  down  with  water  and  allowed  to  slowly 
oxidize.  CuSO4,  together  with  a  good  deal  of  FeSO4  and  Fe2(SO4)3, 
and  H2SO4  form  and  are  leached  out  by  percolating  water  through  the 
heaps.  The  solution  is  run  on  to  fresh  heaps  of  ore,  where  consider- 
able of  the  Fe2(SO4)3  is  reduced  to  FeSO4  by  reaction  with  FeS2  and 
Cu2S.  This  reduces  the  consumption  of  iron  in  the  next  operation, 
in  which  the  liquors  run  over  pig-iron  in  a  series  of  troughs  to  precip- 
itate the  copper.  The  material  cleaned  from  these  troughs  is  screened 
to  remove  scraps  of  iron,  and  the  copper  is  refined. 


COPPER  617 

These  heaps  are  treated  for  years  before  the  last  of  the  available 
copper  is  removed,  but  the  process  may  be  hastened  by  heap  roasting 
the  pyrite,  and  leaching  in  tanks,  though  this  adds  much  to  the  expense. 

In  the  Longmaid  process,  copper-bearing  residues  from  pyrite- 
burning  in  sulphuric  acid  works  are  mixed  with  common  salt,  a  small 
amount  of  raw  pyrite  being  added  if  the  sulphur  does  not  exceed  1§ 
times  the  copper.  The  whole  is  ground  moderately  fine  and  roasted 
at  a  low  temperature  to  avoid  volatilizing  the  copper  chlorides.  The 
following  is  probably  the  main  reaction :  — 

CuO  -f  S02  +  O  +  2  NaCl  =  CuCl2  +  Na2SO4. 

Some  HC1  is  also  formed  and  may  react  with  CuO,  but  most  of  it 
escapes  into  the  stack,  where  it  is  recovered  by  a  water  spray.  The 
roasted  ore  is  leached  twice  with  water,  and  then  with  this  dilute  acid. 
The  second  wash-water  is  used  as  first  wash  on  another  lot  of  ore. 
Copper  is  precipitated  from  the  solution  by  pig-  or  scrap-iron. 

Copper-refining.  —  If  the  copper  contains  no  appreciable  amounts 
of  gold  or  silver,  it  is  refined  by  oxidation  in  a  furnace  similar  to  a 
reverberatory  smelting  furnace,  but  smaller,  to  remove  small  amounts 
of  iron,  sulphur,  arsenic,  etc.  The  old  way  of  getting  complete  oxi- 
dation was  by  a  tedious  flapping  of  the  molten  copper  with  rabbles. 
An  easier  and  more  effective  method  is  to  blow  in  compressed  air  from 
an  iron  pipe,  the  end  of  which  dips  into  the  metal.  Iron  and  other 
metallic  oxides,  including  more  or  less  copper,  are  slagged,  while 
sulphur,  arsenic,  etc.,  volatilize.  During  this  refining,  considerable 
Cu2O  dissolves  in  the  metal  and  must  be  reduced  again,  which  is  done 
by  forcing  wooden  poles  beneath  the  surface.  The  hydrocarbons 
evolved  thoroughly  stir  the  bath,  and  act  jointly  with  the  charcoal  as 
reducing  agents.  The  copper  is  then  cast  in  moulds,  preferably  by 
mechanical  means,  as  in  the  case  of  pig-iron. 

Most  copper  contains  enough  silver  and  gold  to  pay  for  refining  by 
electrolysis,  in  which  process  the  precious  metals,  with  some  other 
impurities,  fall  to  the  bottom  of  the  lead-lined  or  tarred-wood  tank 
in  the  form  of  slime,  while  the  copper  is  deposited  as  a  refined  cathode. 
In  the  common  method  of  arrangement,  a  number  of  anodes  and 
cathodes,  having  an  area  of  6  square  feet  on  each  side,  are  placed  "  in 
parallel,"  1  to  2  inches  apart.  The  anodes  are  plates  of  cast  copper 
about  1  inch  thick  ;  the  cathodes  are  thin  sheets  of  electrolytic  copper, 
which  become  thicker  as  the  refining  progresses.  The  electrolyte  is  a 
12  to  20  per  cent  solution  of  bluestone  with  4  to  15  per  cent  of  free 


618  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

sulphuric  acid.  A  little  hydrochloric  acid  or  common  salt  is  added 
to  precipitate  into  the  slimes  any  silver  that  may  possibly  go  into 
solution  and  which  would  otherwise  deposit  on  the  cathode.  The 
solution  is  circulated  to  maintain  a  uniform  composition,  and  is  kept 
at  a  uniform  temperature  of  40°  to  60°  C.  Impurities  accumulate 
in  the  solution,  portions  of  which  are  periodically  removed  for  purifi- 
cation. The  current  is  commonly  8  to  18  amperes  per  square  foot  of 
total  cathode  surface. 

The  silver  slimes  are  taken  from  the  tanks  at  intervals,  screened 
to  remove  scrap  copper,  and  refined  in  either  of  two  ways :  they  may 
be  treated  with  hot,  aerated  sulphuric  acid  to  dissolve  copper,  washed, 
dried,  and  melted  in  a  small  reverberatory  furnace  with  a  little  sand, 
soda-ash,  and  occasionally  nitre,  to  slag  the  remaining  impurities. 
The  bullion  is  then  parted  to  separate  silver  and  gold  (see  p.  634). 
The  other  method  is  to  add  the  dried  slimes  to  lead  on  a  cupelling 
hearth,  the  silver  and  gold  being  absorbed  by  the  lead,  and  recovered, 
as  described  on  p.  622. 

Because  of  its  properties,  copper  finds  extensive  use  in  the  arts, 
both  in  its  pure  state  and  in  its  many  alloys.  Its  strength,  ductility, 
and  considerable  resistance  to  attack  by  ordinary  atmospheric  and 
chemical  agents,  together  with  its  high  conductivity  for  heat,  make 
it  suitable  for  vessels  and  apparatus  in  various  chemical  works.  It 
is  readily  rolled,  pressed,  or  hammered  into  thin  sheets  or  other  forms, 
but  is  too  ductile  for  working  in  the  lathe.  It  alloys  readily  with  zinc, 
tin,  aluminum,  manganese,  and  phosphorus,  forming  brass  and  bronzes 
which  are  harder  and  stiff er  than  the  pure  metal,  and  may  be  cast 
in  moulds  or  worked  in  the  lathe.  Copper  is  the  best  industrially 
available  conductor  of  electricity;  in  general  the  conductivity  of 
metals  is  greatly  diminished  by  the  presence  of  impurities  in  solid 
solution ;  cuprous  oxide  and  practically  all  metals  dissolve  in  solid 
copper ;  thus  cast  copper,  whether  deoxidized  or  not,  is  unsuited  for 
electrical  work.  Since  neither  metallic  boron  nor  its  oxides  dissolves 
in  copper,  boron  and  boron  sub-oxide  have  been  introduced  for  casting 
copper  for  electrical  work. 


LEAD 

The  chief  lead  ore  is  galena,  PbS;  the  carbonate  and  sulphate 
are  of  some  importance.  The  principal  method  of  reduction  is  in 
blast-furnaces  similar  to  those  used  in  copper-matte  smelting.  As  the 
intense  heat  does  not  extend  so  high  as  in  a  copper  furnace,  the  walls 
for  some  distance  below  the  charging  floor  are  of  brick,  the  lower  part 
only  being  water-jacketed.  The  ore  is  charged  into  the  furnace,  either 
raw  or  after  a  rough  roast.  Formerly,  lead  ores  were  roasted  sweet 
if  they  did  not  contain  much  silver  that  would  volatilize.  Usually 
2  or  3  per  cent  of  sulphur  is  now  left  in  the  ore,  and  often  with  raw  ore 
this  percentage  is  largely  exceeded.  This  procedure  yields  more  matte, 
to  be  roasted  and  resmelted,  yet  it  affords  an  increased  saving. 

Lead  smelters  treat  considerable  quantities  of  gold  and  silver  ores 
that  contain  no  lead,  as  this  is  a  convenient  way  of  recovering  the 
precious  metals. 

In  recent  years  considerable  progress  has  been  made  in  the  blast 
roasting  (often  termed  "  lime-roasting  ")  of  lead  ores  previous  to 
sending  them  to  the  blast  furnace,  and  this  method  has  been  widely 
adopted.  The  sulphide  ore,  sometimes  after  a  partial  preliminary 
roast,  is  roasted  and  sintered  in  pots  with  a  blast  of  air.  Usually 
lime  rock  or  gypsum  is  added  as  a  diluent  and  to  aid  in  slagging. 
These  pots  are  so  built  that  a  blast  of  air  can  be  blown  up  through  a 
grating  'on  the  bottom  on  which  a  coal  or  wood  fire  has  been  made. 
The  ore  and  lime  rock  charge  is  put  on  top  and  a  light  blast  is  turned  on. 
The  sulphur  in  the  ore  ignites  and,  when  the  blast  is  increased,  most 
of  the  charge  is  sintered  together  into  a  large  cake.  After  breaking  up, 
the  caked  material  is  ready  for  the  blast  furnace.  The  capacity  of  the 
blast  furnace  may  be  increased  one-third  by  using  the  blast-roasted 
charge  instead  of  raw  ore.  The  flue-dust  made  and  the  fuel  required 
are  greatly  reduced.  In  place  of  the  pots,  the  Dwight-Lloyd  machine 
(p.  600)  is  often  used. 

The  ore,  sinter,  by-products,  and  the  necessary  fluxes  (usually 
lime  rock  and  iron  ore),  together  with  13  to  16  per  cent  of  coke,  go  to 
the  blast  furnace,  where  the  lead  is  largely  reduced  to  metal  by  the 
coke  and  carbon  monoxide  and  settles  into  the  crucible,  from  the 
bottom  of  which  it  runs  out  through  the  Arents  siphon  tap  (a  sloping 
channel  that  leads  up  from  the  bottom  of  the  crucible  to  a  basin  out- 
side), and  is  removed  to  moulds.  The  matte  and  slag  run  out 

619 


620  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

together,  through  an  opening  above  the  lead,  into  a  small  forehearth 
much  the  same  as  in  a  copper  furnace.  The  slag  runs  away  continu- 
ously from  the  top  of  the  forehearth,  while  the  matte  is  periodically 
tapped  from  the  bottom.  The  cold  matte  is  crushed  moderately 
fine,  and  roasted.  If  low  in  copper,  it  is  then  returned  to  the  regular 
blast-furnaces,  for  which  its  iron  provides  an  excellent  flux ;  but  if  it 
contains  over  10  per  cent  copper,  it  goes  to  a  special  furnace,  yielding 
a  matte  high  in  copper.  The  slag  is  removed  in  large  pots,  in  the 
bottom  of  which  some  extra  matte  may  settle.  This,  together  with  the 
slag  skulls  from  the  pot,  is  re-smelted,  the  waste  slag  going  to  the 
dump.  The  composition  of  the  slag  is  more  important  than  in  cop- 
per-smelting ;  if  too  silicious,  it  takes  up  considerable  lead  oxide ;  if 
too  refractory,  it  requires  a  high  temperature  for  fusion,  and  the  top 
of  the  charge  becomes  too  hot,  increasing  the  loss  of  lead  by  vol- 
atilizing both  sulphide  and  oxide.  Much  of  the  silver  will  be  lost  in 
the  same  way.  Common  slags  contain  33-35  per  cent  SiO2,  about 
55  per  cent  FeO  +  CaO,  the  rest  being  A12O3,  etc. 

Zinc  compounds  are  objectionable,  forming  troublesome  accretions 
on  the  furnace  walls.  They  make  both  slag  and  matte  less  fusible 
and  decrease  the  difference  in  their  specific  gravities,  hindering  good 
separation. 

Reverberatory  smelting  of  lead  ores  was  formerly  much  used,  but 
has  now  been  largely  superseded.  The  ores  need  to  be  rich  in  galena, 
and  should  not  contain  over  5  per  cent  of  silica,  as  the  amount  of  slag 
must  be  very  small,  for  it  coats  the  ore  particles  and  hinders  the  reac- 
tions. The  furnaces  are  comparatively  small  and  of  various  designs. 
The  charge  is  first  roasted,  with  frequent  rabbling,  at  a  moderate  heat ; 
and  when  a  certain  amount  of  lead  oxide  has  been  formed,  the  heat 
is  increased  to  produce  reaction  between  this  oxide  and  the  remaining 
lead  sulphide,  yielding  metal.  The  main  reaction  ie 

PbS  +  2  PbO  =  3  Pb  +  SO2, 

though  others  occur.  As  the  metallic  lead  separates,  it  runs  down 
the  sloping  hearth  into  an  external  basin.  The  charge  is  allowed  only 
to  soften,  quicklime  being  commonly  stirred  in  to  prevent  fusion  which 
would  interfere  with  the  next  roasting  operation.  The  roasting  and 
reaction  stages  are  alternately  repeated  several  times ;  and  toward 
the  end  fine  coal  is  added  to  reduce  the  last  of  the  oxide.  For  a  good 
extraction  the  temperatures  must  increase  in  each  succeeding  reduc- 
tion stage ;  but  in  some  cases,  to  reduce  the  volatilization  losses,  a 
high  temperature  is  avoided,  leaving  more  value  in  the  residue,  which 


LEAD 


621 


FIG.  132. 


is  smelted  in  a  blast-furnace.  This  residue  is  sometimes  treated  in  the 
reverberatory,  at  a  moderately  high  temperature,  being  intimately 
mixed  with  fine  coal. 

The  "  ore  hearth  "  is  a  small  furnace  easily  and  inexpensively 
started  and  stopped,  used  where  the  ore  supply  is  small  and  perhaps 
intermittent;  but  it  is  not  suited  to  argentiferous  ores,  because  too 
much  value  would  be  lost  in  the  fumes.  The  American  water-back 
variety  (Fig.  132  *)  is  a  moderate-sized  basin  made  of  brick  and  lined 
with  cast-iron.  Surmounting  it  on 
three  sides  is  a  cast-iron  wrater- 
jacket  (J),  through  which  pass 
three  tuyeres  (D)  from  the  wind- 
box  (B).  A  wood  fire  is  made  in 
the  basin,  or  hearth,  some  coal 
added,  and  the  blast  turned  on 
through  the  tuyeres.  When  well  heated,  ash  and  clinker  are  removed, 
ore  is  placed  on  the  hot  fuel,  gradually  oxidizing  and  yielding  lead  by 
the  same  reactions  as  in  the  reverberatory  furnace.  The  ore  is  cov- 
ered with  a  thin  layer  of  coal,  and  there  is  the  extra  reaction  2  PbO 
+  C  =  2  Pb  4-  CO2.  When  the  hearth  is  filled  with  lead,  the  latter 
runs  out  over  a  grooved  iron  plate  (G)  into  a  kettle  (H)  kept  hot  by 
a  small  fire,  to  permit  ladling  into  moulds.  The  ore  must  be  low  in 
silica,  and  is  mixed  with  a  small  amount  of  burned  lime  to  prevent 
actual  fusion.  The  charge  is  loosened  and  stirred  by  the  workmen, 
and  the  residue  removed  before  adding  a  fresh  charge. 

Unless  the  ores  are  exceptionally  pure,  the  lead  obtained  by  the 
above  methods  contains  impurities,  which  are  removed  by  slowly 
melting  down  and  stirring  with  a  jet  of  dry  steam.  Arsenic,  antimony, 
tin,  iron,  etc.,  with  some  of  the  lead,  are  oxidized,  and  are  skimmed  off. 

If  the  lead  contains  valuable  quantities  of  silver  and  gold,  they  are 
recovered  generally  by  the  Parkes  process.  After  the  refining  or 
"  softening  "  process,  just  described,  the  lead  is  run  into  a  large  kettle, 
holding  30  tons  or  more,  pure  zinc  is  stirred  in,  the  metal  allowed  to 
cool,  and  a  zinc  crust  (rich  in  gold,  copper,  and  silver)  forms  on  the 
surface.  By  using  only  a  small  amount  of  zinc  at  first  the  gold  and 
copper  can  all  be  removed  without  much  silver ;  and  a  second  zincing 
then  takes  out  most  of  the  remaining  silver,  though  a  third  zincing  is 
usually  needed,  the  crust  from  this  third  treatment  being  used  for  the 
second  treatment  of  another  lot.  If  the  preliminary  softening  is 
omitted,  several  additions  of  zinc  might  be  necessary  to  remove  the 
*  After  Broadhead,  Geological  Survey  of  Missouri,  1873-74,  492. 


622  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

impurities  before  much  of  the  silver  would  be  taken  up  by  the  zinc. 
The  gold  and  the  silver  crusts  are  treated  separately.  They  are  slowly . 
heated  to  "  sweat  out  "  lead,  after  which  they  still  contain  50  per  cent 
or  more  of  lead  alloyed  with  the  zinc  and  precious  metals.  A  better 
way  is  to  lower  the  cylinder  of  a  Howard  press  into  the  desilverizing 
kettle.  When  this  reaches  the  temperature  of  the  lead,  the  crust  is 
skimmed  into  the  cylinder,  which  is  then  raised,  pressure  is  applied 
from  above,  and  the  excess  lead  runs  back  into  the  kettle  through  the 
•perforated  bottom. 

The  zinc  is  removed  from  the  crusts  by  distillation  in  a  graphite 
retort,  a  large  part  being  condensed  and  saved  in  the  metallic  state, 
while  a  portion  is  oxidized.  The  silver  and  gold  remain  in  the  retort 
with  about  5  per  cent  of  the  original  lead,  and  are  recovered  by  cupel- 
lation.  This  consists  in  melting  the  metal  on  a  small  hearth  (of 
crushed  limestone  and  clay,  or  of  Portland  cement  either  alone  or 
mixed  with  ground  fire-brick)  and  oxidizing  the  lead  by  means  of  an  air 
jet,  which  blows  the  lead  oxide  toward  the  front  of  the  hearth,  where 
it  is  skimmed  off.  The  remaining  bullion  is  either  refined  on  the  hearth 
with  nitre  or  by  treatment  in  graphite  crucibles.  Silver  and  gold  are 
parted  as  described  on  p.  634. 

Pattinson's  process  is  sometimes  used  for  this  desilverization  of 
lead.  It  is  based  upon  the  crystallization  of  purer  lead  from  the 
argentiferous  lead  bath.  The  plant  consists  of  large  cast-iron  pots 
in  which  a  temperature  slightly  above  the  melting-point  of  lead 
(335°  C.)  is  maintained.  In  a  pot  near  the  middle  of  the  series  the 
crude  lead  is  kept  in  fusion  for  a  time  and  then  cooled  slightly  while 
thoroughly  stirred ;  when  a  considerable  part  of  the  lead  has  solidi- 
fied, the  crystals  are  fished  out  with  a  perforated  ladle  and  put  into 
the  next  pot  to  one  side,  while  the  liquid  is  ladled  into  the  next  pot 
on  the  other  side.  More  crude  lead  is  run  into  the  'first  pot,  and  the 
process  repeated.  The  crystals  and  liquid  portion  are  each  fused 
and  cooled  again  while  stirring,  a  new  Crop  of  purer  crystals  and  a 
more  concentrated  argentiferous  lead  being  obtained.  This  frac- 
tional crystallization  is  repeated  a  number  of  times,  until  a  de- 
silverized market  lead,  on  the  one  hand,  and  a  highly  argentiferous 
metal,  on  the  other,  is  obtained,  which  latter  is  then  cupelled.  The 
process  can  be  worked  in  only  one  large  pot  by  tapping  off  the  melted 
lead  from  the  crystals,  and  again  refining  each.  Steam  is  generally 
introduced  for  agitation  purposes. 

Lead  shows  a  brilliant  bluish  white  metallic  lustre  on  freshly  cut 
surfaces,  but  tarnishes  rapidly  by  oxidation  in  the  air.  It  is  very 


ZINC  623 

soft  when  pure,  but  impurities  increase  its  hardness.  It  is  very  malle- 
able and  ductile,  but  its  tenacity  or  strength  is  low,  hence  it  is  usually 
worked  by  pressing  or  rolling.  It  melts  at  330°  C.,  and  shrinks  upon 
solidifying  from  fusion.  Its  specific  gravity  is  11.35.  Owing  to  the 
slight  action  of  sulphuric  and  hydrochloric  acids  and  salts  on  the 
metal  in  the  cold,  lead  is  extensively  used  for  chemical  vessels  and 
apparatus,  for  pipes,  drains,  roofs,  etc.  Much  of  it  goes  into  composi- 
tions and  alloys,  e.g.  solder,  pewter,  fusible  metals,  type-metal,  etc. 

ZINC 

Zinc  is  obtained  chiefly  from  blende  (ZnS),  smithsonite  (ZnCO3), 
and  calamine  (Zn2SiO4  +  H2O).  In  New  Jersey,  willemite  (Zn2SiO4), 
zincite  (ZnO),  and  franklinite  (a  complex  oxide  of  zinc,  iron,  and  man- 
ganese) are  important,  the  last  not  being  used  for  the  metal,  but  to 
manufacture  zinc  white,  and  its  residue  utilized  to  make  ferroman- 
ganese.  Blende  must  be  roasted  to  remove  practically  all  the  sulphur. 
Smithsonite  and  calamine  are  often  calcined  (see  p.  599  and  Fig.  127) 
to  get  rid  of  CO2  and  H2O,  though  they  are  sometimes  used  without 
calcining. 

The  pulverized  ore  is  intimately  mixed  with  either  anthracite  coal 
or  with  about  one-third  of  the  total  weight  of  the  mixture  of  coke  and 
soft  coal,  and  is  charged  into  retorts  made  of  clay  (see  Fig.  133,  A). 

The  more  intimate  the  mixture  of  , - 

^£,lu»^WMmmMmmwwim&aar — ipx 

the  charge  the  better ;  consequently  ^^^^Ljim^^^'^^Hmirm -.-- =&^ 
large  plants  use  mechanical  mixers 

which  are  more  effective  than  handwork.  In  the  United  States  cy- 
lindrical retorts,  4  or  5  feet  long  and  8  to  10  inches  in  diameter,  are 
usual.  Several  hundred  are  set  in  a  large  combustion  chamber,  in  a 
nearly  horizontal  position,  but  sloping  gently  toward  the  front.  This 
slope  is  convenient  for  charging  and  discharging ;  and,  if  any  fusible 
slag  forms,  permits  it  to  run  to  the  coolest  part,  where  it  is  least 
likely  to  corrode  the  retort,  which  may  have  a  refractory  lining  of 
chromite  or  magnesia  to  prevent  such  corrosion.  In  mixing  the 
charges,  care  is  used  to  have  them  as  infusible  as  may  be,  adding 
quicklime,  etc.,  if  necessary.  Of  the  common  slag-forming  materials, 
iron  minerals  have  most  frequently  to  be  contended  with.  Iron  pyrite 
is  a  common  associate  of  blende,  and  great  care  is  used  to  remove  it 
before  shipping  to  smelters.  Abroad,  the  retorts  are  larger  and  of 
somewhat  different  shape,  and  there  are  fewer  of  them  to  one  fur- 
nace. The  retorts  are  made  by  machine,  which  yields  a  stronger  and 


624  OUTLINES   OF    INDUSTRIAL   CHEMISTRY 

denser  product  than  if  made  by  hand.  These  qualities  are  important 
on  account  of  the  very  considerable  absorption  of  metal  by  the  retort, 
the  danger  of  losing  metal  through  cracks,  and  the  entrance  of  harmful 
fire-gases.  Heating  is  by  producer  or  natural  gas,  which  gives  better 
control  than  the  old  method  of  direct  firing  with  solid  fuel.  The  air 
for  burning  the  gas  is  pre-heated  by  the  waste  products  of  combustion, 
either  by  the  regenerative  or  the  recuperative  system. 

After  withdrawing  the  residue  from  one  charge  and  filling  with  a 
new  batch,  the  temperature  in  the  retorts  is  gradually  brought  from 
800°  C.  to  1200°  or  1300°  C.  The  zinc  oxide  (and,  less  readily,  the 
silicate)  is  reduced  to  metal,  which  volatilizes  (boiling  point  =  920°  C.) 
and  passes  out  of  the  retort  into  a  condenser  (Fig.  133,  B).  This  is  a 
small,  tubular,  clay  receptacle,  open  at  each  end,  inserted  in  the  open 
end  of  the  retort,  and  exposed  all  round  to  the  air.  Since  metal  con- 
ducts heat  better  than  clay,  a  sheet-iron  "  prolong  "  is  sometimes 
attached  to  the  outer  end  of  the  condenser  to  catch  additional  zinc 
fume  and  to  prevent  air  from  entering  the  condensers  and  oxidizing 
the  metal. 

At  first  the  hydrocarbons  are  distilled  from  the  coal,  and  some  CO2 
is  produced ;  but  later  the  gas  in  the  retort  is  almost  wholly  CO,  from 
the  reduction  of  metallic  oxides  by  the  excess  of  carbon.  The  zinc 
fume  is  oxidized  to  ZnO  by  CO2,  as  well  as  by  free  oxygen,  this  taking 
place  chiefly  at  the  beginning  of  the  distillation.  The  ZnO  mixes  with 
and  coats  fine  particles  of  metallic  zinc,  forming  zinc  dust  or  "  blue 
powder,"  which  makes  up  5  to  10  per  cent  of  the  total  product,  and 
contains  10  per  cent  of  ZnO.  The  quantity  will  be  increased  if  the 
furnace  temperature  is  allowed  to  get  too  low ;  the  metal  cannot  be 
separated  from  it  by  simple  melting,  so  it  is  returned  to  the  retorts  with 
the  fresh  charge.  Both  CO  and  the  uncondensed  zinc  burn  with  a 
bluish  flame,  but  of  distinct  tints ;  the  character  of  this  flame  guides 
the  furnace  men  in  regulating  the  distillation.  The  complete  treat- 
ment of  a  charge  requires  about  24  hours,  and  the  zinc  is  drawn  from 
the  condensers  into  a  kettle  every  8  hours.  The  blue  powder  is 
skimmed  from  the  surface  of  the  metal  in  the  kettle. 

The  most  common  impurities  left  in  the  zinc  are  lead  and  iron,  the 
latter  being  taken  up  to  some  extent  from  the  working  tools.  When 
refining  is  necessary,  it  is  done  in  a  small  reverberatory  furnace  of 
special  design.  At  a  temperature  not  much  above  the  melting  point 
of  zinc  (415°  C.)  the  lead  settles  to  the  bottom  with  very  little  zinc ; 
while  a  zinc-iron  alloy  deposits  on  top  of  the  lead. 

As  galena  is  a  common  associate  of  blende,  a  number  of  methods 


CADMIUM  625 

have  been  devised  to  separate  them ;  but  the  most  successful  is  to  treat 
for  zinc  in  much  the  ordinary  way,  distilling  at  a  lower  temperature 
than  usual  and  treating  the  residue  as  lead  ore.  Distilling  at  higher 
temperatures  vaporizes  too  much  lead  with  the  zinc.  The  recovery 
of  zinc  is  less  than  at  the  temperatures  permissible  with  ores  fairly 
free  from  lead ;  but  the  residue  is  moderately  low  in  zinc,  which  is 
so  troublesome  in  lead  smelting,  and  the  process  thus  makes  many 
ores  valuable  which  would  otherwise  be  useless. 

Zinc  has  a  specific  gravity  of  7 ;  it  melts  at  419°  C.  It  is  brittle 
when  cold,  but  becomes  softer  and  malleable  at  about  120°  C.,  so  that 
thin  sheets  can  be  rolled  from  it,  but  at  200°  C.  it  becomes  so  brittle 
that  it  can  be  pulverized.  It  is  much  used  for  battery  plates  and 
poles ;  in  the  preparation  of  brass  and  other  alloys  with  copper,  tin, 
and  lead.  Since  it  is  only  slowly  attacked  by  atmospheric  agents, 
sheet  zinc  is  largely  used  for  cornices,  roofs,  gutters,  pipes,  etc. ;  also 
to  furnish  a  protective  coating  on  iron,  by  the  process  of  "  galvanizing," 
in  which  the  clean  iron  is  dipped  into  a  bath  of  fused  zinc.  The  zinc- 
iron  alloy  formed  on  the  surface  is  hard  and  brittle  and  lessens  the 
strength  of  the  iron,  but  prevents  rusting. 

CADMIUM 

Cadmium  is  found  associated  with  zinc  to  the  extent  of  4  or  5  per 
cent  in  some  ores.  Commercially  it  is  obtained  as  a  by-product  in 
zinc  smelting.  In  the  reduction  of  the  zinc  (p.  623),  the  cadmium,  being 
more  volatile,  passes  over  first  with  zinc  dust  as  a  brownish  powder. 
This  is  collected  and  distilled  again  at  low  red  heat,  with  reducing 
material.  The  product  contains  some  zinc,  and  further  purification 
is  possible  by  repeating  the  process. 

Cadmium  is  a  silver-white,  lustrous  metal  of  8.55  sp.  gr.  (cast), 
harder  than  tin,  and  of  fibrous  texture.  It  may  be  drawn  into  wire 
or  rolled  into  plate.  It  melts  at  321°  C.  and  vaporizes  at  778°  C. 
It  is  readily  attacked  by  mineral  acids.  Its  chief  use  is  in  the  prep- 
aration of  fusible  alloys  with  bismuth,  tin,  and  lead,  and  for  amalgam 
for  dental  use.  The  iodide  and  bromide  are  used  somewhat  for  photo- 
graphic purposes. 


2s 


TIN 

The  only  commercial  source  of  tin  is  cassiterite  or  tinstone  (SnO2). 
In  the  United  States  this  is  not  found  in  large  quantities,  and  none 
of  the  metal  is  produced  here  from  ore.  A  certain  amount  is  recovered 
from  tin  scrap  by  chemical  solution  and  electrical  precipitation. 

Sometimes  the  cassiterite  after  mechanical  concentration  from 
the  ore  is  still  accompanied  by  considerable  arsenopyrite  (FeAsS) 
and  pyrite  (FeS2),  which  are  injurious  to  the  smelting.  To  remove 
these,  the  ore  is  roasted,  leaving  a  light,  porous  oxide  of  iron,  the  tin 
remaining  unchanged ;  the  iron  oxide  is  removed  by  washing. 

Smelting  is  done  both  in  blast-furnaces  (employed  only  with 
extremely  pure,  lump  ores)  and  in  reverberatories.  The  blast-furnaces 
are  built  of  stone  or  brick  and  clay,  and  the  ore  is  charged  alternately 
with  charcoal,  which  is  used  because  of  its  low  percentage  of  ash. 
To  avoid  the  strong  reducing  conditions  that  would  precipitate  metallic 
iron,  the  furnaces  are  shallow  (the  charge  often  being  only  3  or  4  feet 
deep  above  the  tuyeres),  and  only  a  moderate  blast  pressure  is  used. 
Despite  these  precautions  a  certain  amount  of  iron  is  always  contained 
in  the  metal.  The  tin  and  slag  run  out  together  into  a  small  fore- 
hearth. 

In  the  reverberatory  method  the  ore  is  mixed  with  15  to  20  per 
cent  of  anthracite  or  semibituminous  coal  and  charged  into  the  fur- 
nace, which  is  then  closed,  and  a  good  fire  is  maintained  for  3  or  4 
hours.  The  charge  is  then  stirred,  and  firing  repeated  till  the  reduc- 
tion is  satisfactory.  A  small  amount  of  lime  may  be  used  in  the 
charge  to  slag  the  ash  from  the  intermixed  coal.  When  the  smelt- 
ing is  completed  the  tin  may  first  be  tapped  into  an  external  basin, 
and  then  the  slag  tapped  separately,  or  the  slag  may  be  skimmed 
out  through  a  door  before  tapping  the  metal.  In  the  latter  case  the 
first  portion  of  slag  may  be  sufficiently  free  from  tin  to  throw  away 
at  once. 

Some  of  the  tin  contained  in  the  slag  is  present  as  metallic  parti- 
cles, which  are  occasionally  recovered  by  crushing  and  mechanical 
separation;  but  a  large  part  of  the  slag  must  be  re-smelted  (often 
several  times),  using  either  the  blast  or  the  reverberatory  furnace. 
This  is  done  at  a  higher  temperature  than  in  ore-smelting  in  order 
to  get  the  stronger  reducing  action  needed,  and  scrap-iron  or  iron 
ore  may  be  added  to  assist  the  recovery  of  the  slagged  tin.  Under 

626 


TIN  627 

these  conditions  more  iron  is  reduced  than  in  ore-smelting,  making 
a  poorer  grade  of  tin. 

A  good  deal  of  the  iron  contained  in  the  tin  is  removed  by  liqua- 
tion. The  cast  slabs  are  slowly  melted  on  the  sloping  hearth  of 
a  reverberatory  furnace,  the  tin  running  into  the  external  basin, 
while  the  iron  remains  as  "  hardhead."  This  iron,  however,  still 
retains  some  tin,  and  is  sometimes  added  to  the  slag-smelting  charge. 
Sometimes  liquation  is  performed  by  pouring  the  molten  tin  over 
red-hot  charcoal  on  an  inclined  iron  plate,  the  charcoal  acting  as  a 
filter  to  hold  back  the  "  hardhead."  After  liquation  the  metal  is 
further  refined  by  "  boiling  "  or  "  tossing."  Boiling  consists  in  a 
vigorous  agitation  produced  by  forcing  pieces  of  green  wood  into  the 
metal  bath,  which  is  kept  molten  by  a  fire  beneath  the  kettle.  The 
gases  evolved  from  the  wood  throw  the  metal  into  the  air  in  small 
quantities  at  a  time,  thus  oxidizing  the  impurities,  together  with  some 
of  the  tin.  The  oxides  collect  on  the  surface  as  a  dross,  which  is 
skimmed  off  and  added  to  the  ore  charge.  Tossing  produces  the  same 
result  as  boiling,  and  consists  in  taking  out  ladlefuls  of  the  metal  and 
pouring  it  back  in  a  small  stream.  It  is  a  very  laborious  method, 
and  the  impurities  might  be  oxidized  by  blowing  in  air,  as  in  the  case 
of  copper  refining. 

Tin  has  a  specific  gravity  of  7.285,  and  melts  at  232°  C.  It  is 
a  soft  metal  of  no  great  tensile  strength,  is  rather  brittle  when  cold, 
and  when  bent  emits  a  peculiar  crackling  sound.  At  about  100°  C. 
it  is  malleable,  and  may  be  rolled  into  sheets  (tin-foil)  or  drawn  into 
pipes.  Not  being  corroded  by  water  or  by  most  organic  acids,  it  is 
extensively  used  for  lining  copper  and  iron  tanks,  cooking  vessels, 
etc.  It  forms  valuable  alloys,  as  solder,  bell-  and  speculum-metals, 
bronze  and  Britannia  metal.  On  sheet-iron  it  is  extensively  used  as 
tinned  plate. 


SILVER 

Much  silver  is  obtained  in  copper  and  lead  smelting  (p.  618).  The 
important  silver  ores  are  native  silver,  argentite  or  silver  glance 
(Ag2S),  stephanite  or  brittle  silver  (Ag5SbS4),  pyrargyrite  or  "dark 
ruby  silver"  (Ag3SbS3),  proustite  or  "light  ruby  silver"  (Ag3AsS3), 
cerargyrite  or  "  horn  silver  "  (AgCl),  and  polybasite  [(AgCu)9SbS6]. 
These  are  associated  with  many  other  minerals.  For  the  direct  ex- 
traction of  silver  the  Patio,  Washoe,  and  Reese  River  processes  are 
now  seldom  used.  In  modern  practice,  the  ore  is  generally  leached 
with  cyanide  solution  as  for  gold  ores  (p.  631).  The  dissolving  rate 
of  silver  is  only  two-thirds  that  of  gold  and  stronger  solutions  (often 
one  per  cent)  are  required.  Amalgamation  is  occasionally  employed 
as  with  gold  ores.  In  Cobalt,  Ontario,  high-grade  ores  and  concen- 
trates are  treated  in  tube-mills  with  both  mercury  and  strong  cyanide 
solution.  The  latter  keeps  the  mercury  bright  and  hastens  amal- 
gamation in  addition  to  its  dissolving  action. 

In  the  Patio  process  the  reactions  are  similar  to  those  of  the  Washoe, 
but  the  apparatus  is  crude.  It  is  used  only  in  warm  climates  (Mexico 
and  South  America).  No  heat  is  used  except  from  the  sun  and  that  gener- 
ated by  the  chemical  reactions.  The  fine  grinding  is  done  in  an  arrastra, 
a  pan-shaped  stone  structure  6  to  20  feet  in  diameter.  If  the  ore  contains 
gold,  mercury  is  put  into  the  arrastra,  and  the  gold  amalgam  accumulates 
in  the  bottom  during  a  number  of  charges.  After  grinding,  the  water  is 
drained  off  and  the  pulp  removed  to  the  patio,  a  large,  stone-paved  area 
on  which  the  pulp  is  spread  about  a  foot  deep,  and  salt  scattered  on  it. 
Mixing  is  done  by  driving  mules  through  the  pulp  and  spading  it  over. 
Copper  sulphate  and  mercury  are  in  turn  mixed  in  in  the  same  manner, 
and  the  silver  chloride  is  decomposed  by  the  mercury.  The  process  often 
requires  weeks,  the  recovery  is  not  as  good  as  in  the  Washoe  process,  and 
the  mercury  loss  is  higher. 

In  the  Washoe  process  the  ore  is  pulverized  by  gravity  stamps  to  pass 
a  24  to  80  mesh  screen,  water  being  run  in  continuously.  The  product 
goes  to  settling  tanks  and  the  pulverized  ore  is  shovelled  into  amalgamating 
pans  (Fig.  134  *)  5  feet  in  diameter  and  3  feet  deep,  together  with  some  blue 
vitriol  and  salt.  The  bottom  of  this  pan  has  a  steam-jacket  (S) ;  the  sides 
are  of  wood  lined  with  cast-iron  around  the  bottom.  A  vertical  shaft, 
passing  through  a  central  cone  (C),  carries  mullers  (M)  to  stir  and  grind 
the  charge.  Wings  (W)  on  the  sides  of  the  pan  assist  the  stirring  by  direct- 
ing the  pulp  toward  the  centre.  Removable  iron  plates  (P)  on  the  mullers 
and  on  the  inside  bottom  of  the  pan  take  the  wear  of  grinding.  The  pulp 
is  heated  to  80°  C.  by  live  steam  run  into  it,  and  is  kept  hot  by  steam 
passed  into  the  jacket  (S).  All  the  pulverizing  may  be  done  in  the  stamp 

*  After  Richards,  Ore  Dressing,  Vol.  I.     New  York,  1903. 
628 


SILVER 


629 


battery ;  but  when  grinding  is  necessary,  it  lasts  |  to  4  hours,  during  which 
the  sulphides,  arsenides,  and  antimonides  of  silver  are  converted  into  chlo- 
ride by  the  bluestone  and  salt.  Iron,  worn  from  the  grinding  plates,  or  added 
as  borings,  reduces  the  silver  chloride  :  —  2  AgCl  +  Fe  =  2  Ag  +  FeCl2. 
After  these  reactions  are  completed,  quicksilver  is  sprinkled  in,  and  stir- 
ring (without  grinding)  continued  for  3  to  8  hours  more.  The  pulp  must  be 
of  the  right  consistency 
to  keep  the  quicksilver 
distributed  through  the 
mass.  When  the  mer- 
cury has  taken  up  the 
silver,  the  diluted  charge 
goes  to  a  settler,  and  the 
silver  amalgam  runs  out 
through  a  small  pipe  at 
the  bottom.  The  amal- 
gam is  strained,  retorted, 
and  the  silver  melted 
down  as  for  gold  (p.  631). 

The  Reese  River  pro- 
cess is  used  for  ores 
(arsenic  and  antimony) 
which  do  not  easily 
amalgamate.  The  ore 
is  crushed  dry  and  given 
a  chloridizing  roast  pre- 
vious to  amalgamation. 
This  either  removes  ar- 
senic and  antimony,  or  so 
changes  them  as  to  per- 
mit satisfactory  amalga- 
mation. The  amalgam 
is  treated  the  same  as  for 
gold. 

The  tailings  (waste)  are  often  concentrated  by  mechanical  methods  to 
recover  any  amalgam  and  undecomposed  sulphides  and  arsenides  which 
still  retain  precious  metals.  The  amalgam  is  added  to  that  previously 
obtained,  while  the  sulphides,  etc.,  are  generally  sold  to  smelters. 

Leaching  processes  have  been  considerably  used  for  silver  ores.  In 
the  Augustin  process  the  ore,  after  a  chloridizing  roast,  is  extracted  by  a 
hot  solution  of  common  salt,  and  the  silver  precipitated  by  metallic  copper. 
Patera  used  sodium  "  hyposulphite  "  (thiosulphate)  as  a  solvent  of  the  silver 
chloride,  and  precipitated  the  silver  as  sulphide  with  sodium  sulphide. 
Russell  improved  on  this  by  treating  with  a  double  thiosulphate  of  sodium 
and  copper  after  the  sodium  thiosulphate  leaching;  this  "  extra  solution" 
dissolves  some  of  the  unchloridized  silver  minerals  better  than  the  single 
salt.  Sodium  carbonate  is  added  to  precipitate  lead  before  throwing  down 
the  silver  sulphide.  The  metal  is  recovered  from  the  latter  as  from  the 
slimes  obtained  in  electrolytic  copper  refining  (p.  617). 


FIG.  134. 


630 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


GOLD 

The  chief  occurrence  of  gold  is  in  the  native  state  enclosed  in 
quartz,  with  iron  pyrite  or  other  gangue ;  some  is  obtained  from  tellu- 
rides  of  gold  in  certain  districts.  While  it  is  seldom  visible  to  the  naked 
eye  in  pyrite,  the  microscope  frequently  shows  the  metal  in  thin 
scales  on  the  parting  planes ;  yet  it  may,  in  some  cases,  be  chemically 
combined. 

Some  gold  is  obtained  from  placers  by  washing  the  gravel  through 
long  sluices  filled  with  riffles.  These  are  made  with  cobble-stones, 
wooden  blocks,  or  iron  formed  into  various  shapes  to  produce  eddies 
into  which  the  particles  of  gold  settle  on  account  of  their  high  specific 
gravity  (15.6  to  19.5),  while  the  sand  and  gravel  are  carried  along  by 
the  water.  Mercury  is  sometimes  placed  in  the  riffles  to  amalgamate 
the  gold.  The  more  common  methods  of  recovery  are  by  amalgama- 
tion, or  cyaniding.  Small  amounts  of  gold  are  found  in  many  copper 
and  lead  ores  and  are  recovered  in  the  regular  smelting  processes. 
The  baser  metals  act  as  "  carriers  "  and  the  precious  metal  is  obtained 
in  refining  operations.  Gold  ores  or  concentrates  are  often  added 
to  the  furnace  charge  even  when  they  do  not  contain  either  copper  or 
lead.  When  high  in  silica,  such  ores  are  desirable,  as  they  may  be  used 
instead  of  barren  quartz  in  copper-converting  (p.  616). 

Chlorination,  formerly  an  important  process  of  extraction,  has 
rapidly  fallen  into  disuse.  Amalgamation  is  especially  suited  to 
ores  carrying  free  gold  in  fairly  coarse  particles  (free  milling).  In 

most  other  cases,  cyaniding  is  the  best 
process.  In  recent  years  such  improve- 
ments have  been  made  in  cyanide  work 
that  it  can  now  be  applied  to  almost  all 
types  of  ores. 

In  the  ordinary  amalgamation  pro- 
cess the  ore  is  crushed  to  1-inch  pieces 
by  Blake  or  Gates  breakers  and  fed  to 
gravity  stamps.  Figure  135  shows  two 
5-stamp  batteries.  (A)  is  the  cast-iron 
mortar,  into  the  back  of  which  the  ore 
is  fed  with  water.  The  stamps  (S)  are 
raised,  one  after  another,  by  cams  (T). 

on  the  horizontal  shaft  near  the  top,  and  fall  by  gravity.  Usually 
each  stamp  weighs  800  pounds  or  more,  and  drops  80  to  110  times 
a  minute  through  a  distance  of  5  to  9  inches.  In  the  front  of  the 


GOLD  631 

mortar  is  a  screen  with  holes  0.02  to  0.04  inch  (0.5  to  1.0  mm.)  in 
diameter,  through  which  the  water  carries  the  finely  ground  ore  to 
the  amalgamated  plates.  These  are  sheets  of  copper,  which  have 
been  thoroughly  coated  with  quicksilver  or  a  silver  amalgam,  and 
fastened  to  a  long  sloping  table.  The  bright  particles  of  gold,  and 
any  silver  passing  over  these  plates,  easily  amalgamate  with  and  are 
held  by  the  mercury,  while  quartz,  pyrite,  etc.,  run  off.  Particles  of 
gold  that  are  coated  with  iron-rust  (as  often  happens)  will  not  amal- 
gamate ;  but  an  advantage  of  stamps  over  most  other  fine  grinders 
is  that  they  rub  off  such  coatings.  Grease  also  hinders  amalgama- 
tion, and  special  care  must  be  used  to  prevent  it  dripping  from  any 
of  the  machinery. 

A  small  amount  of  mercury  is  put  into  the  stamp  battery  at  inter- 
vals, or  a  little  is  occasionally  sprinkled  on  the  outside  table  plates, 
in  order  to  keep  the  amalgam  of  proper  consistency.  If  the  amalgam 
is  too  thin,  due  to  excess  of  mercury,  it  will  easily  wash  off;  if  too 
thick,  from  too  little  mercury,  it  will  not  catch  the  gold. 

Once  every  24  hours,  stamping  is  stopped  long  enough  to  scrape 
the  amalgam  from  the  plates.  This  amalgam  often  encloses  fine 
particles  of  ore,  iron,  and  other  dirt,  from  which  it  is  freed  by  grind- 
ing in  a  mortar  with  some  extra  quicksilver,  or  by  other  mechanical 
means.  It  is  then  strained  through  chamois  skin  or  fine  canvas  by 
squeezing.  A  thick,  "  hard "  amalgam,  rich  in  precious  metals, 
remains  in  the  chamois,  while  the  excess  of  mercury,  with  but  little 
gold  or  silver,  passes  through  and  is  used  again.  The  hard  amalgam 
is  distilled  in  a  large  iron  retort,  the  mercury  vapor  passing  off  through 
a  water-cooled  condenser  and  dropping  into  a  vessel  of  water,  while 
the  gold  and  silver  remain  in  the  retort.  The  precious  metals  are 
then  melted  in  a  graphite  crucible  with  borax,  soda,  nitre,  etc.,  to 
remove  the  base  metals  that  have  been  amalgamated. 

The  ore  running  off  of  the  amalgamated  plates  often  contains 
auriferous  pyrite  or  other  valuable  minerals.  It  may  be  cyanided 
directly,  or  treated  on  mechanical  concentrating  tables,  to  wash  away 
the  quartz  and  other  useless  portions,  leaving  the  concentrates  to  be 
smelted  or  treated  by  the  cyanide  process  to  obtain  their  gold. 

The  cyanide  process  is  the  most  important  method  of  treatment 
and  is  extensively  employed. 

Potassium  cyanide  dissolves  gold  according  to  the  equation,  — 

4  Au  +  8  KCN  +  02  +  2  H2O  =  4  KAu(CN)2  +  4  KOH, 
and  silver  by  a  corresponding  reaction.     The  oxygen  dissolved  in 


632  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

the  water  with  which  the  cyanide  solution  is  prepared,  and  the  film 
of  air  attached  to  the  ore  particles  is  generally  sufficient  for  the  above 
reaction,  but  frequently  sulphides,  organic  matter,  etc.,  in  the  ore 
or  the  water  absorb  so  much  oxygen  that  aeration  is  necessary.  This 
is  done  by  drawing  off  the  solution  from  the  bottom  of  the  leaching 
tank  and  pumping  it  back  on  to  the  top,  or  by  forcing  air  into  the 
charge  from  a  perforated  pipe.  The  process  is  conducted  in  large 
vats,  preferably  of  iron,  as  this  has  less  effect  on  the  solution  than 
wood  and  is  cheap  to  keep  in  order.  The  ore,  if  crushed  with  water 
in  gravity  stamps,  is  usually  passed  over  amalgamated  plates  to 
catch  the  coarser  particles  of  gold.  As  the  fine  slimes  interfere  with 
leaching,  the  ore  and  water  are  run  into  settling  tanks  to  catch  the 
sands,  while  the  slimes  overflow  to  be  caught  in  larger  tanks.  The 
settling  of  the  slimes  is  greatly  assisted  by  adding  some  burned  lime  or 
caustic  soda  either  in  the  stamp  battery  or  after  the  ore  leaves  the 
latter.  This  coagulates  the  slimes  and  neutralizes  free  sulphuric 
acid  and  basic  iron  salts  which  are  produced  by  the  decomposition 
of  pyrite,  etc.,  and  which  decompose  cyanide.  Some  ores  require 
roasting  to  get  satisfactory  extraction,  and  so  should  be  dry  crushed. 
Roasting  makes  the  slimes  less  troublesome  to  leach,  so  that  they 
can  be  treated  with  the  sands.  The  sands  are  charged  into  the  leach- 
ing vats,  where  they  may  be  washed  with  water  to  remove  soluble 
salts,  if  this  has  not  already  been  accomplished ;  and  then  with  alkali 
if  necessary.  A  solution  containing  0.25  to  0.35  per  cent  of  potassium 
cyanide  is  then  run  on  (stronger  solutions  are  no  more  effective) 
and  allowed  to  stand  for  several  hours.  It  may  be  removed  and 
pumped  back  for  the  sake  of  aeration,  or  may  be  passed  through  a 
vat  of  fresh  ore,  or  may  be  treated  directly  for  its  dissolved  gold.  A 
second  treatment  is  given  with  a  weaker  cyanide  solution  to  dissolve 
any  gold  remaining  and  to  wash  out  the  adhering  "  strong  "  solution. 
The  last  of  the  cyanide  is  removed  by  a  water  wash.  When  slimes 
are  treated  separately  agitation  is  used,  and  the  solutions  are  not  so 
strong  as  for  sands,  sometimes  containing  0.01  per  cent  or  less  of  KCN. 
After  sufficient  agitation  they  are  allowed  to  settle  and  the  solution 
decanted  through  a  siphon  or  through  holes  in  the  side  of  the  tank,  or 
the  whole  mass  may  be  passed  through  filter-presses. 

To  recover  the  gold  the  solution  is  passed  through  a  series  of 
boxes  filled  with  fine  zinc  shavings,  or  in  some  cases  the  solution  is 
agitated  with  zinc  dust.  What  gold  does  not  drop  to  the  bottom  of 
the  zinc  boxes  is  washed  off  the  shavings  at  the  clean  up.  The  gold 
slime  is  screened  to  remove  bits  of  zinc,  and  then  treated  with  dilute 


GOLD  633 

sulphuric  acid  to  remove  fine  zinc,  etc.,  dried,  and  melted  in  graphite 
crucibles  with  borax,  soda,  sand,  etc.  By  another  method  the  slime 
is  mixed  with  litharge  (PbO),  a  reducing  agent,  borax,  etc.,  and  melted 
in  a  small  reverberatory  furnace  to  produce  a  rich  lead  bullion,  which 
is  cupelled  after  running  off  the  slag. 

As  zinc  precipitation  is  less  efficient  for  solutions  containing  very 
small  quantities  of  gold  than  with  larger  quantities,  the  Siemens- 
Halske  electrical  method  has  been  applied  in  South  Africa  to  the 
dilute  solutions  obtained  from  slime  treatment.  The  anodes  are  iron, 
the  cathodes  lead.  When  enough  gold  is  deposited  the  cathodes  are 
melted  and  cupelled.  This  method  has  been  considerably  displaced 
by  the  Betty-Carter  process,  which  uses  a  zinc-lead  couple  obtained 
by  treating  zinc  shavings  (or  zinc  dust)  with  lead  acetate,  whereby 
lead  is  precipitated  on  the  zinc.  To  make  the  action  of  this  couple 
thoroughly  effective,  some  strong  cyanide  solution  is  added  in  the  pre- 
cipitation boxes.  Aluminum  shavings  may  be  used  instead  of  zinc. 

Gold  ores  almost  always  contain  some  silver,  and  silver  ores 
generally  contain  gold ;  and  in  most  processes  the  two  metals  are 
recovered  together  and  subsequently  "  parted." 

For  chlorination  the  ore  is  first  dead-roasted,  because  sulphides, 
arsenides,  etc.,  envelop  particles  of  gold,  and  consume  chlorine  to  no  pur- 
pose. Roasting  converts  them  into  porous  oxides,  which  the  chlorine  gas 
can  easily  penetrate.  If  lime,  copper  minerals,  or  other  substances  are 
present  which  would  absorb  chlorine  after  roasting,  salt  should  be  added  to 
the  charge  before  completing  the  roast ;  this  chloridizes  them  in  a  cheaper 
way,  but  salt  must  be  added  cautiously  and  in  small  amounts,  for  the  gold 
chloride  formed  is  easily  lost  by  volatilization.  The  gold  is  most  com- 
monly chlorinated  in  large  iron  barrels  lined  with  lead,  the  chlorine  being 
generated  by  the  action  of  sulphuric  acid  on  chloride  of  lime.  The  barrel 
is  supported  horizontally  by  a  trunnion  at  each  end,  and  has  a  manhole 
on  the  side.  Water  is  run  into  the  barrel,  the  proper  quantity  of  sulphuric 
acid  added,  then  the  ore  is  charged,  the  chloride  of  lime  being  put  in  last, 
and  the  cover  immediately  fastened  on  securely.  Another  method  con- 
sists in  having  a  lead  pocket  inside  the  barrel  near  the  top,  into  which  the 
acid  is  poured  the  last  thing  before  putting  on  the  cover.  The  object  is 
to  avoid  generating  chlorine  till  the  barrel  is  tightly  closed.  The  barrel 
is  then  revolved  for  \\  to  6  hours,  depending  on  the  ore ;  this  thoroughly 
stirs  the  charge,  giving  the  gas  free  access  to  every  particle,  and  rapidly 
dissolving  the  gold  chloride  (AuCl3).  Silver  chloride  that  may  be  formed, 
and  other  substances  that  would  coat  the  gold  particles  and  thus  hinder 
the  process,  are  removed  by  the  attrition.  When  the  reaction  is  complete, 
a  cock  is  opened  to  discharge  the  excess  of  gas  through  a  pipe  outside  the 
mill,  the  barrel  is  filled  with  water,  revolved  again,  and  the  solution  poured 
upon  a  sand  filter.  The  barrel  is  again  filled  with  water,  revolved,  the 
solution  poured  through  the  filter,  and  then  the  whole  charge  is  emptied 


634  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

upon  the  filter  and  washed  more  if  necessary.  The  solution  is  run  from 
below  the  false  bottom  of  the  filter-tank  to  a  precipitating  vat.  At  several 
large  plants  the  excess  of  chlorine  is  removed  by  passing  S02  from  burning 
brimstone  through  the  solution.  Hydrogen  sulphide  is  then  introduced, 
precipitating  the  gold  as  sulphide,  thus :  — 

2  AuCl3  +  3  H2S  =  Au2S3  +  6  HC1. 

After  settling,  the  liquor  is  passed  through  a  filter-press  to  save  any  sus- 
pended particles  of  Au2S3.  The  precipitate  in  the  vats  accumulated  from 
a  number  of  charges  is  then  filtered  as  dry  as  can  be,  placed  in  iron  trays, 
and  roasted  in  a  muffle  heated  from  the  top.  This  leaves  metallic  gold, 
which  is  melted  in  a  crucible  with  a  little  borax  and  nitre  to  slag  iron  or 
other  impurities. 

The  vat  process  is  older  than  the  above,  and  although  it  is  less  perfect 
and  takes  more  time,  it  is  still  used  in  small  plants.  The  roasted  ore  is 
moistened  with  just  enough  water  to  cling  together  when  pressed  in  the 
hand,  and  yet  to  crumble  easily.  Chlorine,  at  ordinary  temperatures, 
scarcely  attacks  dry  gold  ;  but  if  the  ore  is  too  wet  it  packs  so  hard  that  the 
chlorine  cannot  penetrate.  The  ore  is  then  carefully  charged  on  a  filter- 
bed  of  crushed  quartz  on  a  perforated  false  bottom  in  a  large  wooden  vat 
painted  with  tar  or  asphalt.  When  the  tank  is  charged,  a  cover  is  luted 
on,  or  closed  with  a  water  seal,  and  chlorine  introduced  through  the  false 
bottom.  The  gas  is  commonly  generated  from  salt,  pyrolusite  (Mn02), 
and  sulphuric  acid.  A  small  hole,  left  in  the  cover  for  the  escape  of  air, 
is  closed  when  the  chlorine  comes  from  it  freely ;  then  the  gas  is  passed 
in  for  an  hour  or  two  longer  to  get  complete  saturation  and  produce  a  cer- 
tain pressure.  The  vat  stands  a  day  or  two,  the  chemical  action  being 
much  slower  than  in  the  barrel  with  its  constant  stirring,  and  then  the 
excess  gas  is  allowed  to  escape  outdoors  or  into  a  holder  for  subsequent 
use.  Water  is  then  run  in  to  cover  the  charge  and  is  drawn  out  from  the 
bottom,  a  stream  running  into  the  top  to  maintain  its  level  above  the  ore. 
The  washing  is  continued  till  practically  no  more  gold  is  dissolved.  As  the 
later  washings  are  poor,  it  is  well  to  keep  them  separate  to  be  used  on 
another  batch.  In  this  process  the  precipitation  is  commonly  done  with 
ferrous  sulphate,  yielding  the  gold  as  metal :  — 

2  AuCl3  +  6  FeSO4  =  Au2  +  2  FeCl3  +  2  Fe2(S04)3. 

This  precipitate  does  not  settle  so  well  as  that  obtained  by  the  use  of  H2S. 
The  gold  is  carefully  dried  and  melted  with  borax,  nitre,  etc. 

Liquid  chlorine  has  been  used  for  chlorinating  gold  ores ;  and,  if  cheap 
enough,  convenience  might  lead  to  its  general  adoption.  One  mill  in 
Colorado  in  a  district  where  the  cost  of  power  to  generate  electricity  is  low 
used  to  make  its  chlorine  by  electrolyzing  salt,*  finding  it  cheaper  than  the 
usual  method. 

Various  methods  of  parting  are  in  use.  For  acid  methods,  the 
melted  alloy  is  either  granulated  by  pouring  into  water  or  is  cast  into 
small,  thin  plates.  It  is  then  boiled  with  strong  sulphuric  acid  in 
cast-iron  pots  to  dissolve  the  silver,  leaving  the  gold  as  a  powder. 


GOLD  635 

For  complete  solution  of  the  silver,  the  alloy  must  contain  2  or  3 
times  as  much  of  that  metal  as  of  gold.  The  silver  sulphate  is  held 
in  solution  by  the  hot  acid  ;  if,  after  the  fire  is  withdrawn,  the  temper- 
ature is  lowered  by  adding  cold  acid,  sulphate  crystals  precipitate 
and  help  to  drag  down  the  finely  divided  gold.  After  removing  the 
solution,  the  residue  is  boiled  twice  with  fresh  acid.  The  gold  is 
washed,  first  with  dilute  acid,  next  with  boiling  water  to  remove  the 
last  of  the  silver,  and  is  then  dried  and  melted.  Some  nitre  and  borax 
are  used  in  this  melting,  if  base  metals  are  still  present.  The  silver 
solutions  are  diluted  with  water,  which  at  first  precipitates  silver 
sulphate  that  is  redissolved  by  heating,  and  the  metal  precipitated 
by  metallic  copper.  After  drawing  off  the  copper  sulphate  solution 
the  silver  is  washed  with  hot  water,  dried,  and  melted. 

Nitric  acid  also  dissolves  silver,  leaving  the  gold,  but  is  more 
expensive  than  sulphuric.  The  first  treatment  is  usually  with  acid 
of  1.2  sp.  gr.,  followed  by  a  second  treatment  with  strong  acid  to 
remove  the  last  of  the  silver,  then  after  diluting  the  solution,  the 
silver  is  precipitated  by  salt.  The  silver  chloride  is  reduced  to  metal 
by  granulated  zinc  in  very  dilute  sulphuric  acid. 

2  AgCl  +  Zn  ->  2  Ag  +  ZnCl2. 

The  Miller  process  is  used  in  Australia  for  bullion  that  contains 
too  little  silver  for  acid  parting,  and  where  silver  bullion  with  some 
gold  is  not  available  to  produce  a  suitable  mixture.  The  bullion  is 
melted  in  a  crucible,  and  chlorine  is  passed  into  it  through  clay  tubes. 
At  this  temperature,  chlorine  combines  with  the  silver,  but  not  directly 
with  the  gold,  and  the  silver  chloride  rises  to  the  surface,  leaving 
the  pure  gold.  Chlorides  of  the  base  metals,  except  copper,  pass  off 
as  fumes.  When  the  action  is  completed,  the  silver  chloride  is  poured 
off,  but  carries  with  it  some  small  shots  of  gold.  Some  double  chloride 
of  gold  and  silver  is  contained  in  the  silver  chloride,  due  to  slight 
attack  on  the  gold.  The  gold  is  reduced  from  this .  by  melting  the 
mass  with  sodium  carbonate  and  borax.  The  silver  chloride  is  then 
cast  into  plates,  which  are  laid  in  a  wooden  frame  alternately  with 
zinc  plates  and  connected  to  the  latter  by  strips  of  silver.  The  frame 
is  placed  in  a  zinc  chloride  solution,  and  the  silver  precipitated  electro- 
chemically,  zinc  passing  into  solution. 

WohrwilTs  electrical  process  is  successful  for  parting  gold  bullion 
carrying  but  little  silver.  The  metal  is  cast  into  plates  and  elec- 
trolyzed  in  a  solution  containing  40  to  45  gms.  of  gold  chloride  and 
20  to  50  cc.  of  concentrated  hydrochloric  acid  per  litre.  The  tern- 


636  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

perature  is  kept  at  65°  to  70°  C.  If  the  acid  is  not  present,  free 
chlorine  is  evolved  at  the  anode  without  dissolving  the  gold.  A 
strong  current  (30  amperes  or  more  per  square  foot)  is  used,  and  the 
required  voltage  is  low,  so  the  cost  of  power  is  small.  The  cathodes 
are  pure  gold  sheets,  arranged  in  multiple.  The  silver  is  converted 
to  chloride  and  settles  in  the  slimes.  If  the  bullion  contains  as  much 
as  10  per  cent  silver,  a  crust  of  silver  chloride  forms  on  the  anode 
and  must  be  rubbed  off ;  much  silver  stops  the  action  entirely.  Os- 
mium and  iridium,  if  present,  pass  into  the  slimes  ;  platinum  accumu- 
lates in  the  solution,  and  may  be  precipitated  with  ammonium  chloride. 
In  order  to  keep  a  constant  percentage  of  gold  chloride  in  the  solu- 
tion, some  is  added  periodically.  This  is  necessary  because  a  certain 
weight  of  gold  is  deposited  at  the  anode  for  every  equivalent  of  silver 
that  is  precipitated  or  of  platinum  dissolved.  The  gold  deposited  on 
the  cathodes  is  almost  chemically  pure. 

The  Moebius  electrical  process  is  used  frequently  for  silver  bullion 
low  in  gold.  The  electrolyte  is  a  dilute  solution  of  silver  nitrate  and 
free  nitric  acid  (1  per  cent  or  less  of  each),  and  the  current  is  12  to 
20  amperes  per  square  foot.  The  anodes  and  cathodes  are  arranged 
in  parallel,  the  former  being  hung  in  muslin  bags  to  catch  the  gold 
slime.  The  cathodes  are  silver  plates,  but  the  deposit  does  not  form 
coherently  on  them  and  is  scraped  off  mechanically  to  prevent  short 
circuiting. 

PLATINUM 

Platinum  is  found  chiefly  in  the  metallic  state  in  placer  deposits, 
usually  alloyed  or  associated  with  iridium,  osmium,  etc.,  and  some- 
times accompanies  placer  gold.  It  also  occurs  in  some  copper  and 
nickel  ores,  as  sperrylite  (PtAss). 

After  washing  the  ore  to  separate  sand  and  gravel,  any  gold  is 
removed  by  amalgamation.  The  ore  is  then  heated  with  dilute 
aqua  regia  under  pressure,  the  solution  evaporated,  and  the  residue 
heated  to  125°  C.  to  convert  any  iridium  or  palladium  into  sesqui- 
chlorides,  and  then  dissolved  in  hydrochloric  acid.  Ammonium 
chloride  is  added  to  precipitate  ammonium  platinic  chloride,  which 
is  decomposed  by  strong  ignition  into  platinum  sponge,  chlorine, 
and  ammonium  chloride,  the  two  latter  passing  off.  The  sponge 
may  be  formed  into  bars  or  sheets  by  compressing,  strongly  heating, 
and  then  hammering  or  rolling. 

Platinum  is  often  contained  in  gold  received  at  parting  works. 
It  may  be  recovered  by  dissolving  the  whole  mass  in  aqua  regia, 


MERCURY 


637 


precipitating  the  platinum  by  ammonium  chloride,  and  throwing 
out  the  gold  by  ferrous  sulphate  or  otherwise.  Another  method  is 
to  melt  the  gold  for  2  or  3  hours  with  twice  its  weight  of  acid  sodium 
sulphate.  The  mass  is  poured  out,  cooled,  and  washed  with  hot 
water.  The  gold  is  dried  and  fused  again  for  several  hours  with  a 
small  amount  of  saltpetre.  The  platinum  enters  the  slags,  which 
are  melted  with  litharge  and  charcoal  to  produce  a  platiniferous  lead 
button ;  this  is  cupelled  to  remove  the  lead,  the  remaining  metal 
dissolved  in  aqutt  regia,  and  the  platinum  precipitated  by  ammonium 
chloride. 

In  the  Wohlwill  process  of  parting  gold  and  silver,  platinum  ac- 
cumulates in  the  electrolyte,  and  is  precipitated  as  the  double  chloride 
of  platinum  and  ammonium,  which  is  ignited  as  above. 

Platinum  is  a  soft,  heavy  metal  (sp.  gr.  21.4),  fusing  at  about  1753° 
C.,  and  having  great  resistance  to  corrosion  by  chemical  agents.  Its 
coefficient  of  expansion  is  nearly  the  same  as  that  of  glass,  so  it  can 
be  sealed  into  tubes  and  bulbs  for  chemical  apparatus  and  electrical 
purposes.  When  alloyed  with  a  little  iridium,  its  hardness  and  inert- 
ness are  increased.  Its  largest  uses  are  for  chemical  apparatus,  sul- 
phuric acid  stills  and  contact  mass,  in  electrical  work  and  for  jewelry. 


MERCURY 

Mercury  is  obtained  from  cinnabar  (HgS)  by  a  combined  roasting 
and  distillation.  Lump  ore  is  treated  in  shaft-furnaces  heated  by 
external  fireplaces,  or 
sometimes  the  fuel  is 
mixed  with  the  charge. 
Hand  reverberatory 
furnaces  are  sometimes 
used  for  fine  ore,  but 
this  is  more  often 
treated  in  a  special 
form  of  shaft-furnace, 
shown  in  Fig.  136.* 
Ore  after  drying  on  the 

platform    (P)    goes    to  FIG  13fJ 

the  feed    hopper    (E) ; 

then  slides  down  the  zigzag  path  formed  by  sloping  shelves  (S) ;  hot 
gases  from  the  fireplace  (A)  pass  in  counter-current  movement  to  the 

*  After  Symington,  Mineral  Industry,  Vol.  VII,  585. 


638  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

ore,  between  the  shelves  to  (B)  and  back  to  (C) ;  thence  to  (D),  and 
from  there  into  condensing  chambers  (G).  The  spent  ore  is  with- 
drawn through  (J).  The  excess  of  air  from  the  fireplace  supplies 
oxygen  for  the  reaction,  - 

HgS  +  2  O  =  Hg  +  S02. 

The  mercury  vapor  and  SC>2  are  carried  by  the  draught  into  the 
chambers  (G),  from  which  the  condensed  mercury  passes  through  (L) 
into  the  collecting  troughs  (T). 

In  some  cases  the  mercury  is  condensed  in  a  long  series  of  brick 
or  cement  chambers,  similar  to  those  shown  in  the  figure ;  in  others 
it  passes  through  a  series  of  zigzag  pipes  which  are  externally  cooled 
by  dripping  water.  These  pipes  are  of  iron  (cemented  inside  to  resist 
the  corrosive  action  of  SO2  and  SO3),  or  of  glazed  clay,  or  even  of 
wood.  The  condensed  mercury  is  drawn  off  from  the  bottom  bends 
of  the  pipes.  At  the  end  of  the  condensers  there  is  commonly  a 
suction  fan  to  deliver  the  gases  and  any  uncondensed  fumes  to  the 
chimney.  The  main  purpose  of  this  fan  is  to  insure  a  suction  instead 
of  a  pressure  in  the  whole  apparatus,  and  thus  prevent  the  poisonous 
mercury  vapor  escaping  from  accidental  cracks. 

On  the  walls  of  the  condensers  a  considerable  quantity  of  "  soot  " 
collects,  consisting  largely  of  fine  globules  of  mercury  mixed  with 
carbonaceous  soot,  ore  dust,  mercuric  sulphate,  etc. .  This  is  mixed 
with  lime  or  ashes,  and  is  treated  by  stirring  and  pressure  in  specially 
designed  pans,  whereby  much  of  the  mercury  is  made  to  coalesce 
and  passes  out  through  holes  in  the  bottom  of  the  pan.  The  residue 
in  the  pan  is  returned  to  the  furnaces,  preferably  being  first  formed  into 
bricks. 

ALUMINUM 

Aluminum  is  produced  by  electrolyzing  alumina  (A^Os)  in  a 
fused  bath  of  cryolite  (Al2Na6Fi2)  in  large  rectangular  iron  pots  with 
thick  carbon  lining.  The  pot  itself  forms  the  cathode,  while  several 
large  graphite  rods  suspended  in  the  bath  serve  as  anodes.  To  start 
the  process,  the  anodes  are  lowered  into  contact  with  the  pot,  and 
powdered  cryolite  is  gradually  introduced  and  melted  by  the  heat  of 
the  arc ;  when  a  large  enough  bath  is  formed,  the  anodes  are  drawn 
J  to  1  inch  away  from  the  lining  of  the  pot.  Some  alumina  is  then 
stirred  in,  and  small  pieces  of  carbon  (old  electrodes)  placed  on  the 
surface  to  prevent  loss  of  heat  by  radiation.  The  resistance  of  the 
cryolite  bath  is  quite  high,  but  drops  when  the  alumina  is  added,  so 


ALUMINUM  639 

that  the  voltage  of  the  cell  is  10  or  less.  A  subsequent  rise  indicates 
that  more  alumina  is  needed  in  the  bath,  since  alumina  and  not  alumi- 
num fluoride  is  decomposed.  Each  anode  carries  250  to  300  amperes, 
and  if  a  short  circuit  increases  this,  the  copper  rod,  to  which  the  anode 
is  fastened,  becomes  very  hot.  The  process  is  continuous,  and  at 
proper  intervals  the  metal  is  ladled  or  siphoned  out.  The  oxgyen 
liberated  at  the  anode  oxidizes  the  latter. 

The  quality  of  the  product  depends  on  the  purity  of  the  alumina 
used.  The  best  grades  are  99.5  to  99.9  per  cent  pure.  The  poorer 
grades,  made  from  unpurified  bauxite,  contain  94  to  96  per  cent 
aluminum,  the  rest  being  iron  and  silicon. 

Bauxite  (hydrated  oxide  of  alumina  with  more  or  less  iron)  is  the 
chief  source  of  the  alumina  as  detailed  on  p.  283  (Bayers'  process) ; 
cryolite  (p.  113)  may  also  supply  a  little. 

Aluminum  is  a  rather  soft  white  metal,  of  low  specific  gravity 
(2.56),  melting  at  655°  C.  It  is  not  readily  oxidized  by  the  air,  nor 
is  it  corroded  by  common  organic  acids,  and  hence  is  suitable  for  cook- 
ing vessels.  It  alloys  readily  with  copper,  tin,  zinc,  and  nickel ;  the 
bronzes  containing  it  are  stronger  and  less  readily  corroded  than 
ordinary  copper  alloys.  It  is  also  used  to  deoxidize  steel  in  casting, 
thus  improving  the  quality  of  the  castings.  It  is,  however,  difficult 
to  solder,  a  fact  which  has  limited  its  uses  very  much. 

Aluminum  alloys  with  copper,  nickel,  zinc,  etc.,  are  made  direct  as 
follows  :  a  rectangular  chest  of  fire-brick  is  lined  with  charcoal  which  has 
been  treated  with  limewater  to  coat  the  particles  with  lime.  Large  carbon 
electrodes  pass  through  opposite  ends  of  the  chest  and  nearly  meet  in  the 
centre.  A  mixture  of  alumina  and  carbon  is  packed  around  the  electrodes, 
and  strips  of  copper  or  whatever  metal  is  to  be  used  for  alloy  are  laid  in  the 
mixture.  A  cover  of  small  charcoal  is  put  in  and  a  brick  cover  luted  over 
all.  The  electric  current  heats  the  charge,  and  the  electrodes  are  then 
gradually  drawn  apart  so  as  to  heat  all  parts  of  the  chest.  This  move- 
ment of  the  electrodes  is  accomplished  automatically  by  a  shunt  circuit 
which  operates  the  vibrating  armature  of  an  electromagnet,  after  the 
manner  of  the  automatic  feed  of  an  arc  lamp,  and  thus  maintains  a  constant 
strength  of  current.  The  aluminum  appears  to  be  produced,  not  by  elec- 
trolysis, but  by  the  reducing  action  of  the  carbon  at  the  extremely  high 
temperature  of  the  electric  arc,  for  the  process  is  as  successful  with  an 
alternating  as  with  a  direct  current. 


640  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

NICKEL 

Practically  all  the  world's  nickel  comes  from  the  nickeliferous 
pyrrhotite  (Fe9Sio)  of  the  Sudbury  district,  Ontario,  and  the  garnier- 
ite  (hydrated  silicate  of  magnesia,  nickel,-  and  iron)  produced  in  New 
Caledonia.  Some  sulphides,  arsenides,  and  antimonides  of  nickel, 
e.g.  nickel  blend,  NiS,  kupfernickel,  NiAs,  etc.,  are  found  in  Saxony 
and  Bohemia.  The  Sudbury  ore  contains  chalcopyrite  (CuFeS2), 
and  the  average  assay  is  about  2  per  cent  each  of  Ni  and  Cu. 

The  ores  are  heap-roasted,  and  smelted  for  matte  (sulphide  of 
nickel,  copper,  and  iron)  and  slag  in  blast-furnaces  like  those  used  in 
ordinary  copper  smelting,  p.  613.  Most  of  the  iron  is  later  removed 
from  the  matte  in  converters  (see  p.  615),  leaving  a  product  with 
about  80  per  cent  Ni  +  Cu  and  nearly  20  per  cent  S.  Oxide  and  sul- 
phide of  nickel  do  not  react  to  give  metal  as  in  the  case  of  ordinary 
copper  matte  (Cu2S  +  2  CuO  =  4  Cu  +  SO2).  Hence  metallic  nickel 
cannot  be  produced  in  the  converter ;  it  would  all  pass  into  oxide  (pro- 
vided the  charge  did  not  freeze).  In  the  Orford  process  the  80  per 
cent  matte  is  smelted  in  blast-furnaces  with  salt-cake  (Na2SO4)  and 
coke;  the  salt-cake  is  reduced  to  Na2S.  When  the  resulting  matte 
settles  and  cools,  the  NiS  is  found  at  the  bottom,  while  the  Cu2S,  FeS, 
and  Na2S  are  largely  combined  in  "  tops,"  these  two  products  being 
easily  broken  apart.  If  the  tops  are  left  to  weather,  their  Na2S  changes 
to  NaOH;  and  upon  melting  with  another  portion  of  nickel-copper 
matte,  the  caustic  passes  again  into  Na2S,  and  another  separation  of 
NiS  is  obtained.  The  bottoms  may  require  a  second  smelting  with 
salt-cake  to  remove  the  remaining  iron  and  copper.  The  nearly 
pure  NiS  is  dead-roasted,  and  the  resulting  NiO  is  reduced  to  metal 
by  fusing  with  charcoal  in  graphite  crucibles. 

In  the  Mond  process,  the  Bessemerized  matte,  nearly  free  from 
iron,  is  dead-roasted,  crushed  to  pass  a  60-mesh  screen,  and  treated 
with  warm  dilute  sulphuric  acid,  which  dissolves  much  of  the  copper 
and  a  little  nickel.  The  residue  is  sent  through  a  reducing  tower 
which  is  25  feet  high,  contains  14  hollow  shelves,  and  has  mechanical 
rabbles  to  move  the  ore  from  one  shelf  to  the  next.  The  upper  seven 
shelves  are  heated  to  250°  C.  by  burning  producer  gas  inside  of  them. 
Water  gas  is  passed  through  the  furnace  in  contact  with  the  ore,  and 
reduces  the  NiO  to  nickel.  The  lower  seven  shelves  are  cooled  by 
passing  water  through  them,  and  the  ore  is  brought  to  50°  C.  It  then 
goes  to  a  volatilizing  tower  (similar  to  the  reducer,  but  not  arranged 
for  heating),  through  which  carbon  monoxide  is  passed.  This  forms 


NICKEL  641 

nickel  carbonyl  (NiC4O4),  which  is  volatile  and  passes  through  a 
filter  to  remove  dust,  and  then  into  a  decomposing  cylinder  filled  with 
granules  of  nickel  and  maintained  at  200°  C.  by  passing  hot  air  through 
internal  flues.  The  Ni(CO)4  decomposes  at  this  temperature,  de- 
positing its  metal  on  the  particles  already  present,  while  the  CO  is 
removed  by  a  fan  and  returned  to  the  volatilizer.  The  grains  of 
nickel  are  continuously  but  slowly  withdrawn  from  the  bottom  of  the 
decomposer  and  screened,  the  small  particles  being  sent  back.  Care 
is  used  that  the  temperature  of  the  reducing  tower  does  not  get  much 
above  250°  C. ;  at  higher  temperatures  Fe2Os  is  reduced  to  iron,  which 
forms  a  carbonyl  in  the  volatilizer,  to  be  carried  along  with  the  nickel 
carbonyl  and  deposit  its  metal  in  the  decomposing  tower.  The  ore 
from  the  volatilizer  returns  to  the  reducing  tower,  and  the  cycle 
between  these  two  must  be  repeated  several  times  to  obtain  a  satis- 
factory extraction. 

In  the  Browne  electrolytic  process,  the  copper-nickel  matte  is 
crushed  to  1  mm.,  given  a  dead  roast,  and  then  reduced  by  charcoal 
in  a  reverberatory  furnace  to  metallic  nickel  and  copper;  half  of 
this  is  cast  into  anodes,  the  other  half  is  granulated  in  water.  The 
granules  are  chloridized  in  a  "  shot  tower  "  by  treating  with  water, 
chlorine,  and  a  little  hydrochloric  acid,  producing  NiC^,  Cu2Cl2,  and 
a  little  FeCl2.  Common  salt  is  also  used  to  dissolve  the  Cu2Cl2. 
This  solution  serves  as  electrolyte  for  the  anodes ;  copper  and  any 
silver  deposit  on  the  cathode,  while  nickel  remains  in  solution.  For 
all  the  nickel  dissolved  from  the  anodes,  a  molecular  equivalent  of 
copper  deposits  on  the  cathodes ;  hence  the  electrolyte  becomes 
gradually  impoverished  in  copper;  and  when  the  solution  finally 
flows  out  of  the  tanks,  it  contains  only  1  part  of  copper  to  80  of  nickel. 
This  copper  is  precipitated  by  Na2S  and  returned  to  the  roasting  fur- 
nace. The  small  quantity  of  FeCk  is  then  oxidized  with  chlorine 
gas,  and  Fe(OH)3  precipitated  by  adding  NaOH.  The  decanted 
solution  is  continuously  evaporated  in  a  special  furnace  until  the  NaCl 
separates;  and  the  remaining  hot  solution  of  NiCl2  is  electrolyzed, 
using  insoluble  anodes  (Acheson  graphite),  which  are  enclosed  in  po- 
rous clay  tubes,  open  at  the  bottom  to  permit  free  circulation  of  the 
electrolyte.  Of  the  chlorine  collected  in  these  tubes  a  small  portion 
is  used  to  oxidize  FeCl2,  as  mentioned  above,  but  most  of  it  passes 
to  the  "  shot  tower  "  to  chloridize  a  fresh  supply  of  metal.  The 
NaCl  from  the  evaporator  is  also  returned  to  the  shot  tower.  The 
HC1  added  to  the  latter  makes  up  for  the  chlorine  lost  in  the  process. 
The  hydrogen  escapes  from  the  tower  to  waste.  An  average  analysis 

2T 


642  OUTLINES    OF   INDUSTRIAL   CHEMISTRY 

of  Mond  nickel  is :  98.32  per  cent  Ni,  0.064  per  cent  Cu,  0.513  per 
cent  Fe,  0.914  per  cent  C,  0.058  per  cent  S,  and  0.034  per  cent  Si. 
Orford  nickel  averages  about  98.6  per  cent  Ni,  0.3  per  cent  Cu,  0.7 
per  cent  Fe,  0.2  per  cent  C,  0.08  per  cent  S,  and  0.05  per  cent  Si. 
The  Mond  and  Orford  products  are  pure  enough  for  steel  manufac- 
ture and  nickel  plating. 

To  obtain  nickel  from  garnierite,  the  latter  is  smelted  in  a  low 
blast-furnace,  either  with  the  calcium  sulphide  waste  from  Leblanc 
soda  manufacture,  or  with  gypsum  (CaSO4,  2  H2O),  which  is  reduced 
to  CaS  by  the  coke.  The  calcium  sulphide  reacts  with  nickel  sili- 
cate to  form  nickel  sulphide  and  calcium  silicate.  As  the  ore  con- 
tains considerable  iron,  some  ferrous  sulphide  is  also  formed  and 
enters  the  matte ;  the  various  silicates  unite  to  form  the  slag.  After 
the  gravity  separation  of  the  matte  and  slag,  the  former  is  either 
treated  in  converters,  or  is  roasted  and  then  smelted  with  sand  (in 
a  blast  or  reverberatory  furnace)  to  slag  the  iron  and  leave  a  second 
matte  containing  much  nickel  and  little  iron.  As  no  copper  is  present 
to  need  separation,  this  matte  is  dead-roasted,  and  reduced  to  metallic 
nickel  by  melting  with  charcoal  in  graphite  crucibles. 

Nickel  is  a  hard,  lustrous,  white  metal  which  fuses  at  1484°  C. ; 
its  specific  gravity  is  8.9.  It  takes  a  high  polish  and  is  stable  in  dry 
air ;  when  exposed  to  damp  it  tarnishes,  but  it  is  not  attacked  by  al- 
kalies. Cast  nickel  contains  carbon  and  is  not  malleable.  Its  elec- 
trical conductivity  is  less  than  that  of  iron,  and  some  of  its  alloys  are 
much  used  in  electrical  work.  It  is  extensively  used  for  plating  iron 
and  other  metals  by  electrodeposition.  The  nickel  coinage  consists 
of  one  part  nickel  to  three  parts  copper.  Over  60  per  cent  of  the 
nickel  now  refined  goes  into  nickel-steel.  Steel  containing  from  1\ 
to.3|  per  cent  of  nickel  has  unusual  strength  and  elasticity.  Invar, 
a  steel  with  about  36  per  cent  of  nickel,  has  practically  no  coefficient 
of  expansion  with  heat.  Monel  metal,  an  alloy  made  by  the  direct  re- 
duction of  copper-nickel  matte,  is  stronger  than  ordinary  steel  and 
has  valuable  acid-resisting  properties.  Because  of  its  great  coloring 
power,  nickel  is  used  to  make  silver-white  alloys  with  copper  or  with 
copper  and  zinc  (e.g.  German  silver). 


SODIUM 


643 


SODIUM 

Sodium  is  produced  from  fused  caustic  soda  by  the  Castner  elec- 
trolytic process.  In  Fig.  137  *  the  caustic  (A)  is  fused  by  gas  jets 
(G).  The  current  passes  from  the  iron 
anode  (F)  to  the  cathode  (H) ;  and,  after 
the  process  is  under  way,  the  current  sup- 
plies enough  heat  to  keep  the  bath  fused. 
Oxygen  is  liberated  at  the  anode,  and  both 
sodium  and  hydrogen  at  the  cathode.  The 
metal,  being  lighter  than  the  electrolyte, 
rises  into  the  covered  receiver  (C)  from 
which  it  is  ladled  out,  or  it  may  run  out 
continuously  through  a  suitably  arranged 
pipe,  while  hydrogen  escapes  through  the  cover ;  the  oxygen  escapes 
around  the  outside  of  the  receiver.  To  prevent  combination  of  the 
oxygen  with  the  sodium  as  they  rise,  a  diaphragm  of  wire  gauze  is  sus- 
pended from  the  receiver  and  surrounds  the  cathode ;  also  the  inner 
diameter  of  the  receiver  is  larger  than  the  outer  diameter  of  the  cathode. 
As  the  decomposition  proceeds,  fresh  caustic  is  introduced  through  (P). 

The  chief  uses  of  sodium  are  for  the  manufacture  of  peroxide  and 
cyanide,  and  in  the  preparation  of  certain  coal-tar  products. 


FIG.  137. 


ARSENIC 

There  is  little  demand  for  metallic  arsenic,  its  chief  use  being  to 
harden  lead  used  for  making  shot,  to  which  it  gives  a  spherical  shape. 
Less  than  1  per  cent  of  arsenic  is  added,  and  this  is  often  reduced 
from  As2O3  in  contact  with  molten  lead,  under  a  cover  of  charcoal. 

Metallic  arsenic  is  obtained  from  mispickel  (FeAsS)  by  a  system 
of  retorts  and  condensers  resembling  those  used  in  the  distillation 
of  zinc,  but  much  smaller.  The  process  is  a  simple  decomposition 
according  to  the  equation,  FeAsS  =  FeS  +  As. 

The  chief  metallurgical  product  is  white  arsenic  (AssOs),  which  is 
used  in  the  manufacture  of  orpiment,  realgar,  Paris  green,  Scheele's 
green,  lead  arsenate  and  other  agricultural  sprays,  etc.  Its  chief 
sources  are  mispickel  and  the  flue  dust  that  results  from  roasting  and 
smelting  certain  lead,  copper,  and  tin  ores.  This  flue  dust  is  charged 
into  a  reverberatory  furnace,  preferably  gas  fired  to  prevent  discolor- 
ing the  product,  and  the  As2O3  resublimed. 

*  C.  F.  Chandler,  Mineral  Industry,  Vol.  IX  (1901),  764. 


ANTIMONY 

Antimony  is  used  to  make  hard  lead  for  type-metal,  for  machinery 
bearings,  for  fans,  blowers,  and  other  apparatus  used  in  chemical 
works,  etc. ;  it  is  alloyed  with  copper  and  tin  for  similar  purposes, 
and  for  pewter  and  Britannia  ware.  A  good  deal  of  antimonial  lead 
is  obtained  in  working  up  the  skimmings  from  softening  furnaces  in 
lead  refineries ;  but  unalloyed  antimony  comes  from  stibnite,  Sb2Sa. 
The  ore  is  ground  moderately  fine  and  is  either  roasted  to  oxide,  which 
is  then  reduced  by  charcoal  in  crucibles,  or  the  SbzSs  is  reduced  directly 
by  metallic  iron,  thus :  — 

Sb2S3  +  3  Fe  =  2  Sb  +  3  FeS. 

Wrought-iron  scrap  and  turnings  (often  tinned  iron  scrap)  and 
ore,  together  with  common  salt  or  salt-cake,  are  mixed  and  charged 
into  crucibles,  each  holding  60  pounds  or  more,  a  sizable  ball  of  the 
scrap  iron  placed  on  top  of  each,  and  a  number  of  the  crucibles  lowered 
into  a  long,  narrow  reverberatory,  through  holes  in  the  roof.  The 
salt-cake  serves  to  flux  the  gangue  minerals  in  the  ore,  and  also  to 
give  a  good  separation  of  the  comparatively  heavy  ferrous  sulphide 
from  the  reduced  antimony.  When  fusion  is  complete,  the  crucibles 
are  removed  and  their  contents  poured  into  cast-iron  moulds.  As 
an  excess  of  iron  is  used,  in  order  to  certainly  reduce  all  the  antimony, 
the  product  contains  several  per  cent  of  iron;  this  is  removed  by  a 
second  melting  with  a  small  quantity  of  clean  stibnite  liquated  from 
the  ore  by  a  moderate  heat.  This  leaves  a  little  sulphur  in  the  prod- 
uct, to  be  removed  by  a  third  fusion  with  some  potash  or  soda.  The 
mass  is  then  poured  into  moulds  and  allowed  to  cool  slowly  before 
breaking  off  the  cover  of  flux.  When  the  work  is  successfully  done,  the 
surface  of  the  antimony  has  a  distinct  crystalline  or  "  starred  " 
appearance. 


644 


BISMUTH  645 

BISMUTH 

Bismuth  is  found  in  Saxony,  Bohemia,  England,  Peru,  Chili,  and 
Australia,  either  as  native  metal  or  in  connection  with  silver,  cobalt, 
nickel,  and  arsenic  ores.  Bismuth  glance  (Bi2S3)  and  bismuth  ochre 
(61203)  are  also  found  associated  as  ofes  to  some  extent. 

The  ores  are  commonly  roasted  to  remove  sulphur  and  part  of 
the  arsenic,  and  then  may  be  reduced  by  fusing  in  crucibles  with 
coal,  iron,  and  flux;  by  this  a  speiss  is  formed,  containing  nickel, 
cobalt,  iron,  and  arsenic,  and  beneath  this  layer  is  the  metallic  bis- 
muth. The  gangue  minerals  mostly  pass  into  the  slag  which  forms 
the  top  layer.  The  speiss  has  a  higher  melting  point  than  metallic 
bismuth,  and  as  soon  as  it  solidifies  on  cooling,  the  bismuth  is  tapped 
off.  The  crude  metal  is  then  liquated  on  a  slightly  inclined  iron  plate, 
at  a  very  moderate  heat,  a  pure  bismuth  flowing  away  from  the  asso- 
ciated impurities,  which  remain  on  the  plate  as  dross;  or  the  anti- 
mony, arsenic,  etc.,  may  be  removed  by  fusion  with  soda  and  nitre, 
the  impurities  passing  into  the  slag.  Oxidized  ores  are  sometimes 
reduced  by  fusion  with  coal  or  iron,  in  crucibles  or  in  reverberatory 
furnaces.  Formerly  the  ores  were  liquated  in  slightly  inclined  iron 
tubes,  but  the  yield  was  not  very  good.  A  wet  process  of  extraction 
is  sometimes  used  for  carbonate  and  oxide  ores,  and  for  litharge  ob- 
tained by  cupelling  argentiferous  lead  containing  bismuth  in  the 
Pattinson  process  (p.  622) ;  this  consists  in  dissolving  in  hydrochloric 
acid  and  precipitating  the  metal  by  inserting  metallic  iron  in  the  solu- 
tion ;  or  the  solution  is  poured  into  water  and  the  precipitated  oxy- 
chloride  is  dried,  after  washing,  and  reduced  with  charcoal. 

Bismuth  is  a  reddish  white,  crystalline,  and  brittle  metal,  melting 
at  about  260°  C.  Its  specific  gravity  is  9.82,  the  hardness  between 
2  and  2.5,  and  the  metal  is  but  little  attacked  by  atmospheric  agencies. 
It  forms  easily  fusible  alloys  with  lead,  tin,  and  cadmium  (Newton's, 
Rose's,  and  Woods's  metal).  The  commercial  metal  usually  contains 
small  quantities  of  silver,  lead,  copper,  iron,  arsenic,  and  sulphur. 
These  are  removed  by  remelting  with  fluxes  in  crucibles,  or  by  other 
special  treatment,  before  the  metal  is  suitable  for  pharmaceutical 
purposes.  The  basic  nitrate  (subnitrate)  finds  considerable  use  in 
medicine  as  an  internal  remedy  in  case  of  stomach  and  intestinal  irri- 
tation, and  as  powder  for  external  application  to  ulcerated  skin  and 
mucous  surfaces. 


646  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

MAGNESIUM 

Magnesium  is  practically  all  produced  by  the  direct  electrolytic 
reduction  of  fused  carnallite  *  (KC1,  MgCy,  to  which  some  common 
salt  or  fluorspar  is  added  as  flux.  The  iron  crucible  is  made  the 
negative  electrode.  Details  ef  the  process  have  not  been  made 
public,  and  the  industry  is  in  the  control  of  a  few  firms. 

The  metal  is  used  in  pyrotechnics  and  as  "  flash  powder  "  and  ribbon 
for  photographic  purposes.  It  is  a  valuable  deoxidizer  in  casting 
copper  alloys,  especially  Monel  metal,  and  its  use  is  steadily  increasing. 

An  alloy  of  magnesium  with  aluminum  is  on  the  market,  under 
the  name  "  magnalium."  It  is  a  silver-white,  very  light  metal,  and 
is  coming  into  use  in  aviation. 

Magnesium  is  a  silver-white  metal,  having  a  specific  gravity  of 
1.74,  and  melting  at  about  750°  C.  It  oxidizes  slowly  in  the  air,  and 
is  attacked  by  hot  water. 

ALLOYS 

While  the  properties  of  many  alloys,  such  as  strength,  hardness, 
etc.,  have  been  known  for  a  great  while,  their  true  nature  was  not 
appreciated  till  the  microscope  and  pyrometer  were  brought  to  the 
aid  of  chemical  analysis  and  mechanical  testing.  The  microscopical 
examination  of  small  sections  that  have  been  carefully  polished,  and 
then  etched  with  suitable  reagents,  shows  that  the  physical  constitu- 
tion of  a  metal  or  alloy  exhibits  in  a  very  marked  way  the  effects  of 
mechanical  or  heat  treatment,  and  often  explains  clearly  the  influence 
of  minute  quantities  of  an  impurity.  A  pyrometer  inserted  in  a  metal 
alloy  that  is  allowed  to  cool  often  shows  a  temporary  halt  in  the  cooling. 
This  indicates  that  one  portion  of  the  metal  is  solidifying  and  giving  out 
its  latent  heat  of  fusion ;  the  cooling  then  continues  till  the  whole  mass 
is  solid.  These  two  lines  of  investigation  have  developed  the  modern 
science,  metallography,  which  has  shown  that  some  alloys  are  definite 
compounds,  some  are  solid  solutions  of  one  metal  in  another,  some  are 
mere  mechanical  mixtures,  and  others  are  combinations  of  these 
conditions. 

The  important  metals  used  for  ordinary  alloys  are  copper,  lead, 
zinc,  and  tin ;  of  minor  importance  are  nickel,  aluminum,  antimony, 
bismuth,  etc.  Iron  alloys  will  not  be  discussed  here,  but  nickel,  chro- 
mium, tungsten,  etc.,  are  important  in  connection  with  steel.  Alloys 
are  often  harder  and  stronger  than  either  of  the  constituent  metals. 

*  Magnesium  chloride  residue  from  the  salt  industry  is  also  said  to  be  used. 


ALLOYS  647 

The  preparation  of  alloys  requires  care  and  skill.  The  least  fusible 
metal  is  melted  first  and  the  more  fusible  added  later,  unless  the  former 
is  used  in  only  a  small  amount.  Sometimes  the  heaviest  metal  is 
added  last  to  prevent  it  settling  to  the  bottom.  Thorough  stirring 
with  a  graphite,  wooden,  or  iron  rod  is  necessary  before  casting.  To 
prevent  oxidation,  it  is  often  necessary  to  cover  the  metal  with  fine 
charcoal.  When  dealing  with  a  volatile  metal,  such  as  zinc,  care  must 
be  used  not  to  have  too  high  a  temperature,  and  not  to  keep  the  alloy 
hot  too  long. 

Following  are  a  few  of  the  important  alloys  :  — 

Brass  is  an  alloy  of  copper  and  zinc,  but  small  quantities  of  lead, 
tin,  etc.,  are  sometimes  added,  either  intentionally  or  because  the  raw 
materials  are  not  pure.  It  is  harder  and  stronger  than  either  copper 
or  zinc,  and  works  much  better  in  a  lathe  or  other  cutting  machine ; 
but  it  is  not  so  ductile  as  the  metals  composing  it.  Copper,  though 
possessing  highly  desirable  physical  properties  (ductility,  strength, 
etc.),  cannot  be  successfully  cast  owing  to  oxidation ;  the  cuprous  oxide 
formed  is  soluble  in  the  metal  itself  and  causes  brittleness  and  blow- 
holes. By  the  addition  of  an  electropositive  metal  this  oxide  can  be 
removed,  zinc  being  most  frequently  used,  a  large  excess  giving  the 
best  result.  Common  yellow  metal,  or  Muntz  metal,  contains  about 
60  per  cent  copper  with  40  per  cent  zinc.  When  intended  for  turning, 
drilling,  or  other  cutting  processes,  the  addition  of  about  2  per  cent 
lead  is  advantageous ;  but  for  rolling  or  hammering,  lead  should  be 
absent,  as  it  causes  the  metal  to  crack. 

Bronze  is  usually  understood  to  be  copper  alloyed  with  tin  up  to 
25  or  30  per  cent,  but  zinc  is  often  present,  and  sometimes  other  metals, 
to  produce  the  desired  qualities.  It  is  used  for  a  variety  of  purposes, 
such  as  machine  parts,  bells,  statues,  medals,  etc.  The  metal  oxidizes 
easily  during  melting,  and  the  tin  is  insufficiently  electropositive  to 
reduce  the  cuprous  oxide  formed.  By  adding  more  electropositive 
elements,  such  as  aluminum,  phosphorus,  or  silicon,  in  small  amounts, 
the  oxide  is  more  effectively  removed,  and  a  homogeneous  dense  and 
strong  product  is  obtained.  Aluminum  bronze  contains  from  2  to  10 
per  cent  aluminum;  phosphor-bronze  contains  from  0.25  to  about 
2.50  per  cent  of  phosphorus  alloyed  as  tin  phosphide.  Ordinary 
bronze  is  rather  brittle ;  but,  if  heated,  and  quickly  cooled  in  water,  it 
becomes  quite  malleable. 

Bearing  metal  or  Babbit  metal,  which  is  largely  used  for  ma- 
chinery bearings,  usually  contains  88.9  per  cent  of  tin,  7.4  per  cent  of 
antimony  and  3.7  per  cent  of  copper. 


648  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

Solders  are  used  as  a  convenient  means  of  uniting  metals  and  must 
melt  at  a  lower  temperature  than  the  metals  to  be  joined.  The 
ordinary  plumber's  or  soft  solder  consists  of  tin  and  lead  in  varying 
proportions.  The  hard  solders  for  uniting  copper,  brass,  etc.,  contain 
copper  and  zinc,  with  occasionally  a  little  tin.  Silver  solder  is  mostly 
silver,  with  a  little  copper  and  zinc ;  and  gold  solder  is  gold,  with  a  little 
copper  and  silver. 

Type  metal  usually  contains  70  to  80  per  cent  of  lead,  20  to  25 
per  cent  of  antimony,  sometimes  a  little  tin,  and  occasionally  copper. 
The  antimony,  etc.,  give  the  necessary  hardness,  and  cause  the  metal 
to  expand  on  cooling  so  as  to  fill  the  moulds  perfectly  and  give  sharp 
impressions.  More  than  25  per  cent  antimony  makes  the  metal  too 
brittle  and  too  hard. 

Aluminum  alloys  are  very  useful  where  light  weight  is  important, 
and  some  of  them  are  also  very  strong. 

Fusible  Alloys.  —  The  melting  temperature  of  an  alloy  is  usually 
less  than  the  average  of  its  component  metals,  and  often  less  than  the 
melting  temperature  of  its  most  fusible  constituent.  For  example, 
the  most  fusible  alloy  of  copper  and  silver,  Cu2Aga  (28  per  cent  Cu,  72 
per  cent  Ag),  melts  at  770°  C.,  while  copper  melts  only  at  1084°  C., 
and  silver  at  960°  C.  Some  alloys,  however,  are  less  fusible  than  either 
constituent ;  SbAl  does  not  melt  till  it  reaches  1080°  C.,  which  is  more 
than  400°  above  either  of  its  metals.  The  most  fusible  commercial 
alloys  are  those  used  for  fusible  plugs  on  automatic  sprinklers  for  fire 
protection;  there  are  several  of  bismuth,  lead,  and  tin  that  melt 
between  90°  and  100°  C.  With  50  per  cent  bismuth,  27  per  cent  lead, 
13  per  cent  tin,  and  10  per  cent  cadmium,  the  melting  point  is  about 
60°  C.  Sodium  and  potassium,  united  in  molecular  proportions,  melt 
at  4J°  C.,  their  individual  fusing  points  being  95°  and  60°. 

Coins.  —  The  United  States  standard  for  gold  and  silver  coins  is 
90  per  cent  of  these  metals,  the  rest  being  copper ;  the  pure  metals  are 
too  soft  to  withstand  wear.  The  standard  in  some  countries  contains 
a  little  less  copper  than  the  above.  The  United  States  standard  for 
nickels  is  75  per  cent  copper  and  25  per  cent  nickel ;  for  one-cent  pieces, 
95  per  cent  copper,  2|  per  cent  tin,  and  2^  per  cent  zinc. 

REFERENCES 

Metallurgy  of  Steel.     Howe,  New  York,  1890. 
Copper  Smelting.     Peters,  New  York,  1895. 
Aluminium.     Richards,  Philadelphia,  1896. 

Introduction   to   the   Study   of    Metallurgy.     Roberts-Austen,   London, 
1902. 


ALLOYS  649 

Text-book  of  Mineralogy.     Dana,  New  York. 

Manufacture  and  Properties  of  Iron  and  Steel.     Campbell,  New  York, 

1903. 

Metallurgy  of  Lead.     Collins,  London,  1899. 
Metallurgy  of  Iron.     Turner,  London,  1900. 
Metallurgy  of  Lead.     Hofman,  New  York,  1901. 
Metallurgy  of  Silver.     Collins,  London,  1900. 
Metallurgy  of  Gold.     Rose,  London,  1902. 
Metallurgy  of  Zinc  and  Cadmium.     Ingalls,  New  York,  1903. 
Metallurgy  of  Steel.     Harbord,  London,  1904. 
Handbook    of    Metallurgy.     Schnabel,    translated    by    Louis.     2   vols., 

London,  1905. 

General  Metallurgy.     Hofman,  New  York,  1913. 

Transactions  of  the  American  Institute  of  Mining  Engineers.     New  York. 
Engineering  and  Mining  Journal.     New  York. 
Transactions  of  the  Institute  of  Mining  and  Metallurgy.     London. 
Metallographist.     Boston. 
Metallurgie.     Halle,  Germany. 
Mineral  Industry.     New  York. 
Mineral   Resources   of   the   United    States.     U.    S.    Geological   Survey. 

Washington. 

Mines  and  Minerals.     Scranton. 
Metallurgical  and  Chemical  Engineering.    New  York. 


INDEX 


"Abraumsalze,"  158. 

Absinthe,  463. 

Absorption  machines  (refrigeration),  24. 

Acetate  of  lime,  "brown"  and  "gray," 

304. 

Acetates,  308. 
Acetone,  305. 
Acetylene,  324. 
Acid,  acetic,  306. 

acetic,  glacial,  307. 

arsenic,  269. 

arsenious,  269. 

boric,  260. 

"chamber,"  62. 

citric,  518. 

hydrochloric,  88. 

hydrosulphurous,  61. 

hyposulphurous,  60. 

lactic,  467. 

muriatic,  88. 

nitric,  137. 

nitrosulphuric,  63. 

oleic,  350. 

oxalic  (as  assistant),  518. 

palmitic,  350,  381. 

pyroligneous,  301,  304. 

stearic,  350,  381. 

sulphuric,  62. 

sulphuric  fuming,  82. 

tannic,  518.  . 

tartaric,  518. 

Acid  Bessemer  process,  605. 
Acid  dyes,  535. 
"Acid  egg,"  73. 
Acker's  electrolytic  cell,  130. 
Acrolein,  350. 
Adsorption,  29,  530. 
"After  treatment"  in  dyeing,  532. 
Agar  agar,  400. 
Aged  black,  544. 

Agitator  for  petroleum  refining,  341. 
Air-gas,  325. 
Air-lift  pump,  74. 
Alcohol,  456. 

"denatured,"  460. 

methyl,  305. 

"proof,"  460. 

rectified,  459. 


Ale,  455. 
Alizarin,  524. 
Alkali  cellulose,  490. 
Alkali  waste,  99. 

Chance-Glaus  process  for  treatment 
of,  105. 

Mond's  process  for  treatment  of,  104. 

Parnell-Simpson  process  for,  111. 

Shaffner-Helbig  process  for,  105. 
Alkaline  process  for  corn  starch,  402. 
Alloys,  646. 
Alum,  285. 

chrome,  288. 

iron,  288. 

"neutral,"  287. 

potassium,  287. 

Roman,  286. 

slate,  286. 

sodium,  287. 

Alumina,  Bayer's  process  for,  283. 
Aluminum,  638. 

acetate,  308. 

alloys,  639. 

salts  as  mordants,  513. 

sulphate,  282,  513. 
Alundum,  267. 
Alunite,  286. 

Amalgamation  process  for  gold,  630. 
Amber,  394. 
Amberite,  484. 
American  vermilion,  243. 
Amide  powder,  475. 
Ammonia,  150. 

Frank  and  Caro  process  for,  150. 

from  animal  refuse,  153. 

from  peat,  153. 

Haber  process  for,  150. 

Serpek  process  for,  151. 
Ammoniacum,  398. 
Ammonia-soda  process,  107. 
Ammonium  carbonate,  155. 

chloride,  154. 

sulphate,  154. 

sulphocyanide,  291. 
Amorphous  phosphorus,  258. 
Amylodextrin,  402. 
Amyloid,  488. 
Aniline  black,  543. 
Annatto,  526. 
Annealing  oven  for  glass,  204,  205. 


651 


652 


INDEX 


Anthracene  oil,  329,  332. 
Anthracite,  34. 
Antimony,  644. 

orange,  242. 

red,  245. 

salts  as  mordants,  516. 
"Anti-scale"  preparations,  51. 
Apatite,  167. 
Archil,  525. 
Argol,  442. 
Arrack,  463. 
Arrastra,  628. 
Arrowroot,  410. 
Arsenic  compounds,  269. 

glass,  269. 
Arsenious  acid,  269. 
Artificial  dyestuffs,  526. 

graphite,  265. 

indigo,  522. 

leather,  583. 

silk,  496. 
Arum,  411. 
Asafostida,  398. 
Asphalt,  347. 
Asphaltene,  347. 
"Assistant"  (in  dyeing),  532. 
Astatki,  as  fuel,  38,  343. 
Attar  of  roses,  391. 
Auxochromes,  527. 
"Available"  chlorine,  134. 
Azides  as  detonators,  484. 
Azo  blue,  545. 
Azo  dyes  (insoluble),  544. 


B 


Babbitt  metal,  647. 
Bacteria,  436. 

"Badische"    contact    process    for    sul- 
phuric acid,  80. 
''Bagasse"  421. 
Bag-filter,  15. 

for  sugar,  430. 
Bakelite,  585. 
Balata  (rubber),  589. 
Ballastite,  484. 
Ball  clay,  213. 
Balling  furnace,  95. 
Ball  mill,  187. 
Balsams,  398. 

Barbier's  tower  system  for  acid,  78. 
Barium  hydroxide,  268. 

peroxide,  272. 
Barkometer,  577. 
Barytes  as  pigment,  230. 
Basic  Bessemer  process  for  steel,  607. 
Basic  dyes,  533. 
"Bating"  of  skins,  576. 
Baudelot  cooler,  452. 
Baume  hydrometer,  26. 
Bauxite  as  source  of  alumina,  639. 


Bayer's  process  for  alumina,  283. 

"Beaming"  of  skins,  576. 

Beating  engine  for  paper-pulp,  559. 

Bee-hive  coke  oven,  35. 

Beer,  444. 

Beeswax,  369. 

"  Beer-fall,"  452. 

Beet  sugar,  425. 

"Bell"  electrolytic  cell,  129. 

Bengal  isinglass,  400. 

Benzine  distillate  from  petroleum,  340. 

Benzoin,  398. 

Benzol,  330. 

Berlin  blue,  233. 

Bessemer  converter  for  steel,  605, 

for  copper,  615. 

Betty-Carter  process  for  gold  precipi- 
tation, 633. 

"Biscuit"  (of  pottery),  216. 
Bismuth,  645. 
"Bittern,"  85. 
Bituminous  coal,  33. 
Black-ash,  97. 

Black  liquor  (pyro  iron),  309. 
Black  pigments,  247. 
Blanc  fixe,  230. 

Blanket  (on  printing  machine),  548. 
Blast-furnace  for  iron,  601. 

for  copper,  613. 
Blast-furnace  slag,  as  cement  material, 

181. 

Blau  gas,  324. 
Bleach  liquor,  131. 
Bleaching,  501. 

of  cotton,  501. 

of  hemp,  509. 

of  jute,  509. 

of  linen,  508. 

of  paper  pulp,  562. 

of  silk,  512. 

of  wool,  510. 
Bleaching  powder,  132. 
Block  printing,  546. 
Blood  as  fertilizer,  165. 
"Bloom"  in  mineral  oils,  342. 
Blotting  paper,  565. 
"Blown  oils,"  362. 
"Blow-ups"  for  sugar  liquor,  429. 
Blubber  oils,  364. 
Blue  glass,  208. 

pigments,  231. 
"Blue  powder,"  624. 
"Bluestone,"  280. 
Blue  vitriol,  280. 
Bock  beer,  455. 
Boetius  furnace  for  glass,  200. 
"Boiled  oil,"  357. 
"Boiled-off"  liquor,  494. 
"Boiled-off  "  silk,  494. 
Boiler  scale,  50. 
Bombonnes,  90, 


INDEX 


653 


Bone-black,  165,  248,  311,  417. 
Bone-char,  165,  311,  417. 

filter,  416. 

"  revivifying,"  418. 
Bone-glue,  570. 
Bone  meal,  165. 

oil,  311. 
Bones,  as  fertilizer,  165. 

distillation  of,  311. 
Borax,  261. 
Boric  acid,  260. 

Boussingault's  process  for  oxygen,  275. 
"Bosh"  (of  blast-furnace),  603. 
"Bouquet"  of  wine,  441. 
"Bran  drench"  for  skins,  577. 
Brandy,  462. 
Brass,  647. 
Brazil  wood,  524. 
Bremen  blue,  235. 
Brewing,  444. 
Brewing-kettle,  451. 
Bricks,  220. 
Brimstone,  roll,  57. 
Erin's  process  for  oxygen,  275. 
British  gum,  412. 
Bromine,  249. 
Bronze,  647. 
Brown  coal,  33. 

pigments,  246. 

powder,  475. 

Browne  process  for  nickel,  641. 
Brunswick  green,  236. 
Bueb's  process  for  cyanide,  289. 
Burgundy  pitch,  394. 
Butter  fat,  367. 
Butterine,  368. 


Cacoa-butter,  366. 
Cadmium,  625. 

yellow,  240. 
Calcerone,  55. 
Calcination,  21. 
Calcium  bisulphite,  60. 

carbide,  266. 

cyanamide,  164,  267. 
Caliche,  145. 

"Calorisator"  for  beet  juice,  425. 
Campbell  open-hearth  furnace,  608. 
Camphor,  389. 

artificial,  389. 
Camwood,  524. 
Canaigre,  521. 
Candles,  380. 
Candle  power  of  gas,  323. 
Cane  sugar,  420. 
Caoutchouc,  586. 
Carbolic  oil,  328,  329,  331. 
Carbonating  tower,  108. 
Carbonation  of  beet  sugar  liquor,  426. 


Carbon  black,  247. 
disulphide,  297. 
tetrachloride,  298. 
"Carbonizing"  of  vegetable  fibres,  499, 

501. 

Carborundum,  264. 
Carburettor  for  water-gas,  312. 
Carmichael's  electrolytic  cell,  126. 
Carmine  (lake),  245. 
Carnallite,  160. 
Carnauba  wax,  370. 
Carter's  process  for  white  lead,  226. 
Cast-iron  still  for  sulphuric  acid,  76. 
Castner's  electrolytic  cell,  128. 

sodium  process,  643. 
"Catalytic     processes"     for    sulphuric 

acid,  79. 
"Catch-all,"  6. 
Catechu,  519. 
Caustic  potash,  162. 
soda,  101,  111. 

soda,  Loewig's  process  for,  102. 
soda,  electrolytic  processes  for,  124. 
Celluloid,  479,  584. 
Cellulose,  487. 
nitrate,  475. 
Cement,  181. 

burning,  182,  185. 
dry  process  of  making,  184. 
kilns,  185,  187. 
Portland,  183,  189. 
pozzuolanic,  181. 
slag,  181. 
testing,  191. 

wet  process  of  making,  184. 
Cementation  process  for  steel,  609. 
Centre-bit,  336. 
Centrifugal  machine,  18. 

sugar,  429. 

Ceramic  industries,  212. 
Ceramics,  215. 
Ceresine,  347. 
Chamber  acid,  62,  66. 
"Chamber  crystals,"  64. 
Chamber  process  for  white  lead,  225. 
Chamois  leather,  581. 
Champagne,  443. 
Chance-Glaus   process   for   tank-waste, 

105. 

"  Chaptalized"  wine,  443. 
Charcoal,  34. 

oven-retorts  for,  302. 
Chardonnet-Lehner  artificial  silk,  496. 
Chemical  pulp,  555. 
Chemical  theory  of  dyeing,  529. 

of  tanning,  583. 

"Chemick,"  in  bleaching,  502,  505. 
Chestnut  extract,  520. 
Chili  saltpetre,  145. 
China  clay,  212. 
grass,  492, 


654 


INDEX 


Chinese  blue,  234. 

red,  243. 

vermilion,  244. 

wax,  369. 

white,  229. 
Chip  casks,  453. 
Chlorates,  135. 
"  Chloride  of  lime,"  132. 
Chloridizing  roast,  594. 
Chlorination  of  gold  ores,  633. 
Chlorine  industry,  115. 
Chlorine,  Deacon's  process  for,  118. 

Donald's  process  for,  122. 

Dunlop's  process  for,  121. 

electrolytic  process  for,  124. 

Mond's  process  for,  123. 

Schloesing  process  for,  121. 

Weldon's  apparatus  for,  117. 

Weldon-Pechiney  process  for,  123. 
Chondrin,  568. 
Chrome  alum,  288. 

greens,  236. 

orange,  239. 

red,  239,  243. 

tannage,  580. 

yellows,  238,  545. 
Chromium  salts  as  mordants,  513. 
Chromogens,  527. 
Chromophores,  527. 
Cider,  444. 

vinegar,  466. 
Cinnabar,  637. 

Clark's  process  of  water  purification,  50. 
Claus  sulphur  kiln,  106. 
Clay,  analysis,  214. 

ball,  213. 

"fat,"  213. 

fire,  213. 

primary,  212. 

secondary,  212. 
Closed  pots  for  glass,  201. 
Coal  gas,  314. 
Coal-tar,  327. 

dyestuffs,  527. 
Cobalt  blue,  235. 
Cochineal,  525. 
Cocoanut  fibre,  492. 
Coffey  still,  12. 
Coin  alloys,  648. 
Coke,  35. 
Coke  tower,  90. 
"Cold  test"  for  oils,  345. 
Collagen  (in  skins),  572. 
Collodion,  479. 

Colloidal  substances  in  water,  48. 
Colloids,  28,  30. 
Colophony,  393. 

Color  mixing  for  textile  printing,  548. 
Colored  glass,  207. 

leather,  579. 
Combination  tannage,  580. 


Compound  glass,  207. 
"Compound  lard,"  360,  367. 
Compression   machines    (refrigeration) , 

23. 

"  Concentrated  alum,"  282. 
Concentrates,  593. 
Concentration  of  ores,  593. 

of  sulphuric  acid,  74. 
Concrete  sugar,  423. 
Condensers  for  gas  works,  317. 
"Conditioning"  of  silk,  493. 

of  wool,  498. 

Contact  process  for  sulphuric  acid,  79. 
Converter  for  glucose  making,  414. 
Copal,  395. 
Copper,  611. 

converting,  615. 

smelting,  611,  613. 
Copper-arsenic  greens,  238. 
Copper  greens,  237. 

leaching  processes,  616. 

refining,  617. 

salts  as  mordants,  516. 

smelting,  611,  613. 
Copperas,  279. 
Copperas  vat  for  indigo,  543. 
Coprolites,  168. 
Cordite,  483. 
Coriin  (in  skin),  572. 
Corium  (of  skin) ,  572. 
Corn  oil,  360. 
.  starch,  402. 
Cornish  stone,  218. 
Cotton,  487. 
"Cotton-ball,"  262. 
Cotton  bleaching,  501. 

dyeing  with  acid  dyes,  536. 

dyeing  with  aniline  black,  544. 

dyeing  with  azo  dyes,  544. 

dyeing  with  basic  dyes,  534. 

dyeing  with  direct  dyes,  533. 

dyeing  with  indigo,  542. 

dyeing  with  ingrain  dyes,  543. 

dyeing  with  mineral  dyes,  545. 

dyeing  with  mordant  dyes,  537. 

dyeing  with  sulphide  dyes,  540. 

mercerizing  of,  489. 
Cotton-seed  "foots,"  360. 

oil,  360. 

stearin,  360. 
Coupler's  still,  12. 
"Coupling"  in  dyeing,  533. 
"Crabbing"  of  mixed  wool  goods,  510. 
"Cracking"  of  oils,  340. 
"Crazing"  of  pottery  glaze,  219. 
Cream  of  tartar,  442. 
Creosote  oil  from  coal-tar,  329,  332. 

from  wood-tar,  310. 
Crown  filler,  231. 

glass,  206. 
Crucible  of  blast-furnace,  602. 


INDEX 


655 


Crucible  process  for  steel,  609. 

Crutcher  for  soap,  376. 

Cryolite  soda  process,  113. 

Crystallization,  19. 

Cudbear,  525. 

Cupellation,  622. 

Curcuma,  526. 

Currying,  579. 

Cut  glass,  206. 

Cutch,  519. 

Cyanides,  289. 

Cyanide  process  for  gold,  631. 

"Cyan  salt,"  294. 

Cylinder  machine  for  paper,  564. 

Cylinder  oil,  343.      . 


D 


Dammar,  395. 

"Dandy  roll"  for  paper  machine,  565. 

Date  palm  sugar,  420. 

Deacon's  process  for  chlorine,  118. 

"Dead  oil,"  330. 

"Dead  roasted"  ore,  594. 

Decoction  method  of  mashing,  450. 

Defecation  of  sugar-cane  juice,  422. 

of  sugar-beet  juice,  426. 
"Degras,"  581,  583. 
Dephlegmation,  11. 
Depilation  process  for  skins,  575. 
Destructive  distillation  of  bones,  311. 

of  wood,  301. 
"Detonation,"  470. 
Deville's  process  for  oxygen,  276. 
"Devitrification"  of  glass,  196. 
Devulcanization  of  rubber,  589. 
Dextrin,  402,  412. 
Dextrose,  413,  418. 
Diastase,  445. 
Dietzsch  kiln,  185. 
Diffusion  method  of  sugar  extraction, 

422,  425. 

Digesters  for  wood  pulp,  555,  557. 
"Dippel's  oil,"  311. 
Direct  dyes,  532. 

"Discharge"  for  textile  printing,  549. 
Disperse  system,  28. 
Displacement  process  of  nitration,  478. 
"Dissolved  bone,"  165. 
Distillation,  9. 

of  wood,  301. 
Distilled  liquors,  456. 
Divi-divi,  520. 

"Doctor"  (on  printing  machine),  547. 
Donald's  process  for  chlorine,  122. 
Dongola  process  for  leather,  580. 
"Downcomer"  of  blast-furnace,  601. 
Down-draught  kiln  for  pottery,  217. 
"Dragon's  blood,"  395. 
"Driers"  for  boiled  oil,  357. 
"Drips"  for  sulphuric  acid  chamber,  71. 


"  Drying"  of  oils,  351. 

Dunlop's  process  for  chlorine,  117,  121. 

Durgen  system  for  corn  starch,  403. 

Dwight-Lloyd  sintering  machine,  600. 

Dyed  blacks,  544. 

Dyeing,  methods  of,  530. 

theories  of,  529. 
Dyes,  acid,  535. 

acid-mordant,  539. 

adjective,  528. 

basic,  533. 

direct,  528,  532. 

ingrain,  543. 

mineral,  545. 

monogenetic,  528. 

poly  genetic,  528. 

substantative,  528. 

sulphide,  540. 

vat,  541. 
Dynamite,  481. 


E 


Eau  de  Javelle,  131. 

de  Labarraque,  131. 
Ebonite,  591. 
Ecru  silk,  494. 
Edge-runner,  352. 
Elaidin  test  of  oils,  355. 
Electric  furnace  products,  264. 
Electrical   methods   for   steel   making, 

610. 
Electrolysis  apparatus,  Acker's,  130. 

bell,  129. 

Carmichael's,  126. 

Castner's,  128. 

"gravity,"  129. 

Griesheim-Elektron,  127. 

Hargreaves-Bird,  126. 

Le  Sueur,  126. 

Rhodin,  129. 

Townsend,  127. 

Whiting,  128. 
Electrolytic  methods  for  chlorine  and 

caustic  soda,  124. 
Elemi,  397. 

Emerald  green  (pigment),  238. 
Enamel,  209,  219. 
Encaustic  tiles,  218. 
Enfleurage,  387,  388. 
"Engine  sized"  paper,  563. 
Engobe  (glaze),  219. 
Enzymes,  435. 
Epsom  salts,  161. 
Equilibrium  relationships  over  carbon, 

40. 

Eria  silk,  495. 
Esparto,  492,  561. 
Essential  oils,  387. 
Ethiops  mineral,  244. 
Euphorbium,  399. 


656 


INDEX 


Evaporation,  3. 

by  multiple  effeot,  6. 
Evaporators,  Kestner's,  7. 

Lillie,  8. 

multiple  effect,  6. 

Yaryan,  6. 

Exhauster,  for  gas,  317. 
Explosives,  470. 
"  Extract"  in  beer,  454. 
Extraction  process  for  oils,  353. 
Extraction  of  juice  from  sugar-cane,  421. 
Extracts  (tannin),  521. 


Faience,  217. 

"Fat"  clay,  213. 

"Fat"  lime,  175. 

Fatty  oils,  349. 

Feldmann's  ammonia  apparatus,  152. 

"Felting"  of  wool,  498. 

Fermentation,  435. 

bottom,  441,  452. 

top,  441,  453. 

vacuum,  454. 
Ferric  nitrate,  148. 
Ferromanganese,  606. 
Ferrous  acetate,  309. 

nitrate,  148. 

sulphate,  279. 
Fertilizers,  164. 
Fibres,  487. 

animal,  492. 

vegetable,  487. 
Fibroine  of  silk,  492. 
Filtration,  14. 

bone-char,  416. 

sand,  19. 
Filter-press,  15. 
Fire  brick,  221. 

clay,  213. 

"Fire-test"  for  oils,  344. 
"First  sugar,"  423. 
Fish  glue,  570. 

oils,  363. 

Fish-scrap,  as  fertilizer,  166. 
"  Flash  point"  of  oils,  344. 
Flavine,  526. 
Flax,  490. 

"Floaters"  in  glass  furnace,  200. 
Flowers  of  sulphur,  57. 
Forcite,  483. 

Fourdrinier  machine  for  paper,  564. 
Fractional  condensation,  10. 
Frankincense,  399. 
Frasch  method  of  mining  sulphur,  57. 

process  for  caustic  soda,  111. 
French  column,  12. 

"Friction  coating"  (rubber  cloth),  591. 
Fuels,  32. 

gaseous,  38. 

liquid,  38. 


Fuller-Lehigh  mill,  189. 
Fulminates,  484. 
Fumcroles,  260. 
Fuming  acid,  nitric,  141. 

sulphuric,  82. 
Furnace,  balling  (black-ash),  95. 

Campbell  open-hearth,  608. 

glass,  199. 

muffle,  21. 

reverberate ry,  21. 

revolving,  22,  598. 

Ropp  (mechanical),  596. 

shaft,  22. 

Siemens'  regenerative,  44. 

White-Howell,  598. 
Fusel  oil,  458,  461. 
Fusible  alloys,  648. 
Fustic,  526. 


Galalith,  586. 

Galbanum,  399. 

Galland  process  for  malting,  447. 

"Gallized"  wine,  443. 

Galls,  519. 

Galvanizing,  625. 

Gambier,  520. 

Gamboge,  241,  399. 

Garbage  as  fertilizer,  166. 

Gas,  air,  325. 

analyses,  325. 

blast-furnace,  43. 

Blau,  324. 

coal,  39. 

Mond,  43. 

natural,  38. 

oil,  323. 

producer,  41. 

purifying,  320. 

purifying  Feld  process,  321. 
Gas  liquor,  151,  322. 
Gas  producer,  Siemens',  42. 

Taylor's,  42. 
Gay-Lussac  tower,  71. 
Gelatine,  568,  570. 

dynamite,  483. 
Gelis  process  for  ammonium  sulphocya- 

nide,  290. 

Giant  powder,  482. 
Gin,  462. 
Glass,  196. 

amber,  207. 

annealing,  204. 

black,  209. 

blue,  208. 

colored,  207. 

furnaces,  199. 

"gall,"  203. 

green,  207. 

iridescent,  209. 


INDEX 


657 


Glass  —  Continued. 

"milk,"  208. 

"opal,"  208. 

pots,  201. 

process  of  making,  202. 

red,  208. 

refining,  203. 

"tough,"  207. 

violet,  208. 

yellow,  207. 

Glatz  process  for  glycerine,  385. 
Glauber's  salt,  93,  161. 
.  Glazes,  219. 
Glover  tower,  70. 
Glucose,  412,  418. 
Glue,  568. 

Gluten  from  starch,  404,  407. 
Glutin,  568. 
Glycerides  in  oils,  349. 
Glycerine,  384. 

chemically  pure,  385. 

crude,  385. 

Glatz  process  for,  385. 

Van  Ruymbeke  process,  384. 
Gold,  630. 

"Grainer"  process  for  salt,  86. 
"Graining"  soap,  375. 

morocc*o  leather,  582. 
Granulator  for  sugar,  432. 
Grape  sugar,  413,  414. 
Graphite,  artificial,  265. 

as  pigment,  248. 

"Gravity"  cell  for  electrolysis,  129. 
"Green"  malt,  446. 
"Green"  oil,  332. 
Green  pigments,  236. 
"Green"  starch,  405. 
Green  vitriol,  279. 
Griffin  mill,  188. 
Griesheim-Elektron     electrolytic     cell, 

127. 
Grillo-Schroeder    contact    process    for 

sulphuric  acid,  81. 
"Grog,"  213. 

Griineberg-Blum  ammonia  still,  152. 
Guaiacum,  396. 
Guano,  r67. 
Guayule  (rubber),  586. 
Guignet's  green,  237. 
Gum,  399. 

acacia,  399. 

Arabic,  399. 

Senegal,  399. 

tragacanth,  400. 
Gum-resins,  398. 
Guncotton,  475. 
Gunpowder,  471. 
Gutta  percha,  591. 
Guttman's    apparatus   for   nitric    acid, 

138. 
Gypsum,  193. 

2u 


Hand  frame  for  paper  making,  564. 
"Handling"  of  hides  in  tanning,  578. 
Hard  rubber,  591. 
Hardness,  temporary,  of  water,  49. 

permanent,  of  water,  50. 
Hargreaves-Robinson      salt-cake      pro- 
cess, 92. 

Hargreaves-Bird  electrolytic  cell,  126. 
Hart's  apparatus  for  nitric  acid,  139. 
Hasenbach-Clemm  contact  process,  81. 
Hasenclever-Deacon  process,  120. 
Haubold  washing  machine,  502. 
Heap  roasting  of  ores,  599. 
Hemlock  bark  as  tannin  source,  520. 
Hemp,  491. 

bleaching,  509. 

Manila,  492. 

oil,  359. 

Hermite  bleaching  process,  508. 
Herreshoff  pyrites  burner,  68. 
Hide  substance,  573. 
Hides  for  leather,  573. 
"High  wines,"  458. 
Hoffmann  furnace,  185. 
"Hollander"  for  paper  pulp,  559. 
Honey,  413. 
"Hop-back,"  451. 
Hydraulic  lime,  178,  182. 

main,  316. 

.press,  353. 

Hydrochloric  acid,  88. 
Hydrogen  peroxide,  272. 

bleaching,  508,  512. 
Hydrogenation  of  oils,  351. 
Hydrolysis  of  fats,  351. 

of  starch,  413. 
Hydrometer,  specific  gravity,  25. 

Baume's,  26. 

Twaddell's,  26. 

Hydrosulphite  vat  for  indigo,  542. 
Hypochlorites,  131. 
Hyraldite,  61. 


Iceland  moss,  400. 
Illuminating  gas,  312. 

(water  gas),  312. 
India  rubber,  586. 
Indian  red  (pigment),  243. 

yellow  (pigment),  241. 
Indigo,  235,  521. 

artificial,  522. 

carmine,  522. 

extract,  522. 

vats,  541. 

Infusion  method  of  mashing,  449. 
Ingrain  colors,  543. 
Invar,  642. 


658 


INDEX 


Iodine,  252. 

Iodine  value  of  oils,  355. 

Irish  moss,  400. 

Iron,  601. 

alum,  288. 

buff,  515,  545. 

reds,  243. 
Isinglass,  571. 
Ivory  black, .  247. 


Japan,  358. 
Japan  wax,  367. 
"Jars,"  336. 
Jute,  491. 

bleaching,  509. 


Kainite,  161. 

Kaolin,  212. 

Kauri,  395. 

Kelp,  113,  252. 

"Kemp,"  in  wool,  498. 

Kent  mill,  189. 

Keratine,  498,  572. 

Kermes,  526. 

Kerosene  from  petroleum,  339. 

Kessler's  acid  concentrator,  76. 

Kestner's  acid  elevator,  73. 

evaporator,  7. 
Khaki,  545. 

Kier  for  cotton  bleaching,  504. 
Kieserite,  160,  161. 
Kilns,  22. 

Dietzsch,  185. 

Hoffmann  ring,  185. 

pottery,  217. 

revolving,  22,  187. 
Kino,  520. 

Kips  (for  leather),  573. 
Kirschwasser,  463. 
Koechlin's  bleaching  process,  507. 
Kremnitz  process  for  white  lead,  227. 
Kumiss,  444. 


Lac,  396. 

dye,  396,  525. 

"stick,"  396. 
Lactic  acid,  467. 
Lager  beer,  455. 
Laid  paper,  565. 
Lake,  black,  248. 

carmine,  245. 

cochineal,  246. 

Florentine,  246. 

madder,  246. 

yellow,  246. 


Lampblack,  247. 
Lanolin,  370. 
Lard,  367. 

oil,  365. 

"Layers"  for  hides  in  tanning,  578. 
Lead,  619. 
Lead  acetate,  309. 

arsenate,  270. 

chambers  for  acid  making,  70. 

chromate,  239,  243. 

glass,  197. 

nitrate,  147. 

oxide,  241,  242. 

plaster,  379. 

refining,  621. 

smelting,  619. 
Leaf  filter,  17. 
"  Lean"  clay,  213. 
Leather,  572. 
Leblanc  soda  process,  94. 
"Lehr"  for  glass  annealing,  204. 
Le  Sueur  electrolytic  cell,  126. 
"Level"  dyeing,  532. 
Levigation,  2. 
Levulose,  413. 
Lignite,  33. 
Light  oil  from  coal-tar,  328,  330. 

from  wood-tar,  309. 
Lillie  evaporator,  8. 
Lima  wood,  524. 
Lime,  175. 

air-slaked,  178. 

hydrated,  179. 

hydraulic,  178,  182. 

"lean"  or  "poor,"  175. 
"Lime  boil"  in  bleaching,  504. 
Lime  glass,  197. 
Lime  kilns,  175. 
Liming  of  skins,  575. 
Lind6  process  for  oxygen,  277. 
Linen,  490. 

bleaching,  508. 
Linseed  oil,  357. 
Linseed-oil  varnish,  397. 
Liqueur,  463. 
Liquid  glue,  570. 
Litharge,  241. 
Lithopone,  230. 
Litmus,  525. 
Liver  oils,  364. 
Lixivia tion,  2. 

Shank's  process  for,  98. 
Loaf  sugar,  433. 

Loewig's  process  for  caustic  soda,  102. 
Logwood,  523. 

Longmaid  process  for  copper,  617. 
Lowe  process  for  water-gas,  312. 
"Low  wines,"  461. 
Liickow  process  for  white  lead,  228. 
Lunar  caustic,  149. 
Lunge-Rohrman  plate  tower,  91. 


INDEX 


659 


Lyddite,  485. 

"Lye  boils"  in  bleaching,  505. 

M 

Madder,  524. 

bleach,  503. 

flowers,  524. 

lake,  246. 

style  (textile  printing),  550. 
Magnalium,  646. 
Magnesium,  646. 
Maize  oil,  360. 
Majolica,  217. 

Malachite  green  (pigment),  237. 
Maletra  burner  (pyrites),  68. 
Maltha,  347. 
Malting,  445. 
Manganese  brown,  545. 

steel,  610. 
Manila  hemp,  492. 
Maple  sugar,  420. 
Market  bleach,  506. 
Martin's  process  for  wheat  starch,  407. 
Mashing,  448. 
"Masse  cuite,"  423. 
"Massicot,"  241. 
Mastic,  394. 
Matches,  258. 

Mather-Thompson  process,  507. 
Matte,  611. 

Maumene  test  for  oils,  355. 
McDougal  roasting  furnace,  596. 
Mechanical  pulp  (wood),  554. 

theory  of  dyeing,  529. 
Melinite,  485. 
Melter  for  sugar,  429. 
Menthol,  390. 
Mercerizing,  489. 
Mercury,  637. 
Metallurgy,  593. 
Methyl  alcohol,  305. 
Methylated  spirit,  460. 
Military  explosives,  485. 
Milk  glass,  208. 
Miller  process  for  "parting"  gold  and 

silver,  635. 

Milner's  process  for  white  lead,  227. 
Mimosa  bark  as  tannin  source,  521. 
Mineral  dyes,  545. 
Mineral  oils,  334. 
Mining  powders,  475. 
Mirrors,  209. 
Moebius  process  for  "parting"  bullion, 

636. 
Molasses,  from  cane  sugar,  424,  425. 

beet  sugar,  427. 

recovery  of  sugar  from,  427. 
Molybdenum  steel,  610. 
Mond's  chlorine  process,  123. 

nickel  reduction  process,  640. 


process  for  tank-waste,  104. 

producer  gas,  43. 
Monell  process  for  steel,  609. 
Monel  metal,  642. 
Mordant  dyes,  536. 
Mordants,  512. 
Morocco  leather,  582. 
Mortar,  179. 
Moulds,  435. 
Mountain  blue,  235. 

green,  237. 
Muffle  furnace,  22. 

roaster,  89. 

Multiple  effect  evaporation,  6. 
Muriatic  acid,  91. 
Muriate  of  tin,  516. 
Muscovado  sugar,  423. 
Musk,  artificial,  395. 
"Must,"  440. 
Myrabolans,  520. 
Myrrh,  399. 

N 

Nankin  yellow,  545. 
Naphtha,  330. 
Naphthalene,  332. 
-Natural  dyestuffs,  521. 
Natural  gas,  38. 
"Neutral  oils,"  342. 
Neutralizer  for  glucose  making,  415. 
Nickel,  640. 

steel,  610. 

"Nigre"  from  soap,  376. 
Nitrates,  145. 

ammonium,  147. 

barium,  149. 

ferric,  148. 

ferrous,  148. 

lead,  147. 

potassium,  146. 

silver,  149. 

sodium,  145. 

strontium,  149. 
"Nitrate  of  iron,"  148. 
Nitre-cake,  138. 
Nitre  pot,  67. 
Nitric  acid,  137. 

Birkeland-Eyde  process  for,  142. 

Bradley-Love  joy  process  for,  142. 

fuming,  141. 

Guttmann's  apparatus,  138. 

Hart's  apparatus,  139. 

Pauling's  process,  144. 

Rhenania  process,  140. 

Schoenherr  process,  143. 

Valentiner's  process,  140. 
Nitrocellulose,  475. 
Nitrogelatine,  483. 
Nitrogenous  waste  as  fertilizer,  166. 
Nitroglycerine,  479. 


660 


INDEX 


Nitrolim,  267. 
Nitrosulphonic  acid,  65. 
Nitrosylsulphuric,  acid,  63. 
"Nitrous  vitriol,"  72. 
Nut-galls,  519. 

O 

Oak  bark  as  tannin  source,  520. 

Oil  of  vitfiol,  62. 

Oil  tannage,  581. 

Oil  testing  (mineral  oils),  344. 

(fatty  oils),  354. 
On  well  drilling,  336. 
Oil,  almond  (essential),  390. 

bergamot,  390. 

blackfish,  365. 

blubber,  364. 

cajaput,  390. 

cassia,  391. 

castor,  361. 

cedar,  390. 

chamomile,  390. 

Chinese  wood,  357. 

cinnamon,  391. 

clove,  391. 

cocoanut,  366. 

cod-liver,  364. 

colza,  361. 

corn,  360. 

cotton-seed,  360. 

earthnut,  362. 

eucalyptus,  391. 

fish,  363. 

geranium,  391. 

Gingili,  361. 

hemp,  359. 

lard,  365. 

lavender,  391. 

lemon,  391. 

linseed,  357. 

liver,  364. 

maize,  360. 

menhaden,  363. 

mustard,  391. 

neat's-foot,  365. 

"oleo,"  365. 

olive,  362. 

origanum,  392. 

palm,  366. 

palm-nut,  366. 

peanut,  362. 

peppermint,  391. 

pogy,  363. 

poppy,  359. 

porpoise,  364. 

rape-seed,  361. 

rose,  391. 

rue,  392. 

sassafras,  392. 

sesame,  361. 


shark-liver,  364. 

soja  bean,  359. 

sperm,  368. 

spike,  391. 

sunflower,  359. 

tallow,  365. 

thyme,  392. 

train,  364. 

tung,  359. 

turpentine,  388. 

whale,  364. 

wintergreen,  392. 

wormwood,  392. 
Oils,  drying,  357. 

marine  animal,  363. 

non-drying,  362. 

semi-drying,  359. 

terrestrial  animal,  365. 
Olein,  350,  382. 
Oleomargarine,  368. 
Oleo-resins,  398. 
Olibanum,  399. 
Opal  glass,  208. 

Open-hearth  process  for  steel,  607. 
Orange  mineral,  241. 
"Ore-dressing,"  593. 
"Ore-hearth"  for  lead  smelting,  621. 
Orford  process  for  nickel  reduction,  640. 
Origanum,  392. 

Orleans  process  for  vinegar,  464. 
Orpiment,  240. 
Oven,  bee-hive,  35. 

Otto-Hoffmann,  36. 

Semet-Solvay,  37. 

Simon-Carves,  36. 

Oxidation  style  (textile  printing),  550. 
Oxidizing  roast  for  ores,  594. 
Oxygen,      Brin-Boussingault      process, 
275. 

Deville's  process,  276. 

Linde  process,  277. 

Tessie  du  Motay  process,  276. 

by  electrolysis  of  water,  277. 
Ozokerite,  346. 


Palmitin,  350. 

Pan  process  for  salt,  85. 

Paper,  554. 

Paper  making,  562. 

Paraffine  oils,  342. 

Paranitraniline  red,  545. 

Parchment,  582. 

paper,  565. 
Paris  green,  238. 

Parnell-Simpson  process  for  alkali,  111. 
Parkes'   process  for  desilverizing  lead, 

621. 

"Parting,"  gold  and  silver,  634. 
"Pasteurizing,"  442. 


INDEX 


661 


Patent  leather,  579,  582. 
Patio  process  for  silver,  628. 
Pattinson's    process    for    desilverizing 

lead,  622. 

Pauli's  process  for  "tank-liquor,"  99. 
Pauli-Fremery  artificial  silk,  497. 
Pearlash,  156. 
Pearl  sago,  410. 
Peat,  33. 

Pebble  powder,  474. 
Perborates,  263. 
Perchlorates,  135. 
Permanganates,  299. 
Permutite   process   for  water   purifica- 
tion, 52. 

Pernambuco  wood,  524. 
Peroxide,  barium,  270. 

hydrogen,  270. 

sodium,  271. 
Persian  berry,  526. 
Petrolene  (in  asphalt),  347. 
Petroleum,  composition  of,  335. 

crude,  338. 

industry,  334. 

refining,  339. 
Phenol,  331. 
Phlobaphenes,  577. 
Phosphate  rock,  168. 
Phosphatic  slag,  171. 
Phosphorites  as  fertilizer,  167. 
Phosphorus,  256. 

amorphous,  258. 
Physical  theory  of  tanning,  583. 
"Pickling"  of  timber  and  wood,  332. 
Picrates,  484. 
Pig-iron,  604. 
Pigments,  222. 

black,  247. 

blue,  231. 

brown,  246. 

green,  236. 

orange,  241. 

red,  242. 

yellow,  238. 

Pigment  style  (textile  printing),  549. 
Pipe-column,  78. 
Pitch  from  coal-tar,  333. 
"Pitching"  (before  fermenting  a  wort), 

452. 

Placers,  630. 
Plantation  rubber,  587. 
Plaster  of  Paris,  193. 
Plastics,  584. 
Plate  glass,  204. 
Plate  tower  (Lunge),  77. 
Platinum,  636. 
"Plumping"  of  hides,  574. 
Pneumatic  malting,  447. 
Pontianak,  586. 
Porcelain,  215. 
Porter,  455. 


Portland  cement,  183. 
Potash,  caustic,  162. 

from  alunite,  158. 

from  seaweed,  158. 

industry,  156. 
Potassium,  bichromate,  162. 

bromide,  251. 

carbonate,  162. 

chlorate,  135. 

chloride,  162. 

cyanide,  294. 

ferricyanide,  293. 

ferrocyanide,  292. 

nitrate,  146. 

permanganate,  299. 

persulphate,  136. 

sulphate,  161. 
Potato  starch,  408. 
Pozzuolanic  cements,  181. 
Press-cake    from    oil    industry    as    fer- 
tilizer, 166. 
Pressed  glass,  206. 
Primary  clay,  212. 
"Priming,"  of  boiler  water,  51. 
Printing  paper,  565. 
Producer  gas,  41. 
"Proof  spirit,"  460. 
Proof  stick,  431. 
Prussian  blue,  233,  546. 
"Puering"  of  skins,  576. 
Pulke,  444. 
"Pulled"  wool,  498. 
Purification  of  water,  48. 
Purifiers  for  gas,  320. 
Purpurpine,  524. 
"Putrid  soak"  for  hides,  574. 
Pyknometer,  27. 
Pyrites  burners,  67. 

Herreshoff,  68. 

Maletra,  68. 

Spence,  68. 

Wedge,  69. 

Pyroligneous  acid,  304. 
Pyroxyline,  479. 

Q 

Quebracho  extract,  521. 
Quercitron,  526. 

Quick  cook  system  for  wood  pulp,  557. 
"Quick"  vinegar  process,  465. 


Rack-a-rock,  485. 

Rags  as  paper  stock,  561. 

Ramie,  492. 

Rape-seed  oil,  361. 

Raschen's  process  for  cyanide,  290. 

Realgar,  245. 

"Reclaimed"  rubber,  589. 


662 


INDEX 


Rectification  of  alcohol,  459. 
Rectifier,  12. 

Recuperative  heating,  44. 
Red  glass,  208. 

lead,  242. 

ochre,  243. 

phosphorus,  258. 

pigments,  242. 

prussiate  of  potash,  293. 
"Red  liquor,"  308. 
"Red  oil," '382. 
Reduced  oil,  343. 

Reese  River  process  for  silver,  629. 
Refrigeration,  23. 
Regenerative  heating,  42. 
Relation    of    constitution    to    color    of 

dyes,  527. 

Rendering  of  fats  by  steam,  354. 
Resins,  393. 

"Resist,"  for  textile  printing,  549,  551. 
Retting  of  flax,  490. 
Reverberatory  furnace,  21. 
Reversion  of  superphosphate,  170. 
Revivifying  of  bone-char,  418. 
Rhenania  process  for  nitric  acid,  140. 
Ricks  for  evaporating  brine,  4,  84. 
Roasting,  21. 

of  ores,  594. 
Roburite,  485. 
Rock  salt,  83. 

Roller  (machine)  printing,  547. 
Roman  alum,  286. 

cements,  182. 
Rongalite,  61. 

Ropp  roasting  furnace,  596. 
Rosendale  cement,  182. 
Rosin,  393. 

grease,  394. 

oil,  394. 

soap,  373. 

spirit,  393. 

"Rosin  change"  for  laundry  soaps,  376. 
Rouge,  243. 
Rubber,  586. 

cement,  591. 

compounding,  588. 

"devulcanized,"  590. 

"reclaimed,"  589. 

substitutes,  589. 
Rum,  463. 
Russian  leather,  582. 

petroleum,  343. 


Safety  explosives,  482. 
Safety  matches,  259. 
"Saggars"  for  pottery,  216. 
Sago,  410. 

Saladin  system  of  malting,  448. 
Salammoniac,  154. 


Salsoda,  100. 
Sal  volatile,  155. 
Salt,  83. 
Salt-cake,  92. 

furnaces,  88. 

"Salt  glaze"  for  pottery,  216. 
Saltpetre,  146. 

"Salt  water"  in  glass  furnace,  203. 
Sandarac,  394. 
Sand-filters,  19. 
Sand-lime  bricks,  180. 
Saponification  of  fats,  351,  381. 

by  acid,  382. 

by  lime,  381. 

by  Twitchell's  process,  381. 

value,  355. 
Sappan  wood,  524. 
Self-hardening  steel,  610. 
Semet-Solvay  coke  oven,  37. 
"Seneca  oil,"  335. 
Separator,  6. 
Sepia,  247. 
Sericine,  492. 
Sesame  oil,  361. 
Sewage  as  fertilizer,  173. 
Shaft  furnaces,  22. 

for  zinc  ores,  599. 
Shale  oil  industry,  345. 
Shank's  lixiviation  process,  97. 
Shellac,  396. 
Shimose,  485. 

"Shivering"  of  pottery,  220. 
"Short  flame  burning,"  22. 
Siemens'  gas  producer,  42. 
Siemens-Halske    electrical    method    of 

gold  precipitation,  633. 
Siemens'  regenerative  furnace,  43. 
Sienna,  240. 
"Silent  spirit,"  459. 
Silk,  492. 

artificial,  496. 

bleaching,  512. 

"boiled-off,"  494. 

dyeing,  532,  534,  536,  539. 

ecru,  494. 

glue,  492. 

souple,  494. 

tussah,  495. 

wild,  495. 
Silver,  628. 

nitrate,  149. 

Simon-Carves  coke  oven,  36. 
"Singeing"  of  cotton  cloth,  503. 
Sisal,  492. 

Sizing  of  paper,  563. 
Skins,  572. 

"Skipping"  of  sugar,  431. 
"Skivers,"  579. 
"Slabber"  for  soap,  377. 
Slag  cement,  181. 
Slag  fertilizer,  171. 


INDEX 


663 


"Slip"  (prepared  clay),  215. 
Slow-cook  sulphite  process  for  wood- 
pulp,  558. 
Smalt,  234. 

Smokeless  powder,  483. 
Soap,  372. 

"boiled-down,"  377. 

Castile,  373,  378. 

"cold-process,"  374,  375. 

laundry,  375. 

milled,  378. 

mottled,  378. 

"olein,"  373. 

powder,  379. 

remelted,  378. 

scouring,  379. 

soft,  373. 

toilet,  378. 

transparent,  378. 
Soap  frames,  376. 
Soap  kettles,  374. 
Soda-ash,  100,  110. 
Soda,  ammonia  process  for,  107. 

cryolite  process  for,  113. 

crystals,  100. 

industries,  94. 

Leblanc  process  for,  94. 

process  for  wood-pulp,  555. 
Sodium,  643. 

acetate,  309. 

arsenate,  270. 

arsenite,  270. 

bicarbonate,  100,  111. 

bisulphite,  59. 

carbonate,  100. 

chlorate,  136. 

bromide,  251. 

hydrosulphite,  60. 

hyposulphite,  61. 

nitrate,  145. 

peroxide,  273. 

thiosulphate,  61. 
"Sod  oil,"  581. 
Soffioni,  260. 
Soft  sugars,  433. 
Soft  water,  47. 
Solar  salt,  84. 
Solder,  648. 
Sole  leather,  578. 

Solid  solution  theory  of  dyeing,  529. 
"Solidified  bromine,"  251. 
Souple  silk,  494. 
"Sour"  in  bleaching,  505. 
Sour  process  for  wheat  starch,  407. 
Spanish  grass,  561. 
"Sparger,"  450. 
Special  steels,  610. 
Specific  gravity,  25. 
Spence's  burner  for  sulphide  ore,  68. 
Spermaceti,  369. 
Spiegeleisen,  606. 


Spindle  oils,  343. 

Spirit,  "methylated,"  460. 

"proof,"  460.  . 

"silent,"  459. 

varnishes,  397. 
Spirits  of  turpentine,  388. 
Splitting  of  skins,  579. 
Sprengel  explosives,  485. 
"Spueing,"  of  leather,  574. 
"Staking,"  of  leather,  580. 
Stamp  mill,  630. 
Starch,  401. 

arrowroot,  410. 

cassava,  411. 

corn,  402,  406. 

"green,"  405. 

potato,  408. 

rice,  409. 

sago,  410. 

wheat,  407. 
Stassfurt  salts,  158. 
Steam  black,  544. 

Steam  style  for  textile  printing,  549. 
Stearin,  350. 
Steel,  604,  605. 

Bessemer,  605. 

cementation,  609. 

crucible,  609. 

open-hearth,  607. 
Stick  lac,  396. 
Still,  Coffey,  12. 

Coupier,  12. 

French  column,  12. 
Stills,  for  chlorine,  116. 
Stockholm  tar,  310. 
Stoneware,  216. 
Stout,  455. 

Stoves,  for  heating  blast,  603. 
"Stoving"  of  wool,  511. 
"Strike  pan,"  for  sugar,  423. 
Strontium  nitrate,  149. 

process  for  recovery  of   sugar  from 

beet  molasses,  427. 
"Stuffing"  of  leather,  579. 
Style  (in  textile  printing),  549. 
Sublimation,  14. 
"Sublimed"  white  lead,  229. 
Sucrose,  420. 
"Sugar  of  lead,"  309. 
Sugar  refining,  428. 
Suint,  157,  500. 

Sulphate  process  for  wood-pulp,  558. 
Sulphates,  279. 
Sulphatizing  roast,  594. 
Sulphite  process  for  wood-pulp,  555. 
Sulphur,  55. 

Glaus  kiln  for,  108. 

derivatives,  58. 

Tromblee-Paull  burner,  59. 

Wise  burner  for,  58. 
Sulphur  dyes,  540. 


664 


INDEX 


Sulphuric  acid,  62. 

cast-iron  stills  for,  76. 

catalytic  processes,  79. 

concentration  of,  74. 

diagram  of  manufacture,  66. 

fuming,  82. 

glass  stills  for,  75. 

Kessler's  apparatus,  76. 

platinum  stills,  75. 

reactions  for,  63. 

silica  dishes  for  concentration  of,  74. 
Sumach,  519. 
Sunflower  oil,  359. 
"Superheater"  for  water-gas  carburet- 

ting,  312. 
"Superphosphate,"  169. 

double,  171. 
Surface  phenomena,  28. 
Suspenders  for  tanning  hides,  577. 
"Sweating,"  of  hides,  575. 
"Sweet  waters"  (glycerine),  383,  384. 


Tallow,  367. 

bone,  367. 
Tangential  chambers   (sulphuric  acid), 

70. 

Tank  furnace,  for  glass,  200. 
"Tank  liquor,"  98. 
"Tankage,"  166. 
Tank  waste,  103. 
Tannin,  518. 
Tanning  processes,  577. 

with  oils,  581. 
Tapioca,  411. 
Tar-stills,  327. 

for  petroleum  residuum,  341. 
Tawing  of  skins,  579. 
Terra  alba,  231. 
Terra  cotta,  220. 
Terra  verde,  238. 
Terrestrial  animal  oils,  365. 
Tessie  du   Motay  process  for  oxygen, 

276. 

Testing  of  cement,  191. 
Testing  of  oils,  344,  354. 
Textile  industry,  487. 
Textile  printing,  546. 
Thelan's  pan,  100,  110. 
Thenard's  process  for  white  lead,  226. 
Thickening    agents    (textile    printing), 

548. 

Thymol,  390. 
Tiles,  218. 
Tin,  626. 

salts  as  mordants,  516. 
"Tin  spirits,"  516. 
Tinkal,  261. 
Tissue  paper,  565. 
Tourills  for  acid  condensation,  90. 


Townsend  electrolytic  cell,  127. 
Tragacanth,  400. 

Tromblee-Paull  sulphur  burner,*  59. 
Tube-mill,  188. 
"Tub-sizing"  (of  paper),  563. 
Turkey-red  bleach,  506. 
"Turkey-red  oil,"  362. 
Turkey-red  on  cotton,  537. 
Turmeric,  526. 
Turpentine  varnish,  397. 
Tussah  silk,  495,  512. 
Tuyeres  of  blast-furnace,  601. 
Twaddell's  hydrometer,  26. 
Type-metal,  648. 


Udells,  252. 
Ultramarine,  231. 

blue,  232. 

green,  232. 

red,  233. 

violet,  233. 
Umber,  246. 

Ungumming  of  silk,  494. 
Unhairing  process  for  skins,  575. 
"Union"  goods  in  dyeing,  533. 
Up-draught  kilns,  217. 
Upper  leather,  578. 


"Vacuum  process"  for  beer,  454. 

Valentiner's  nitric  acid  process,  140. 

Valonia,  520. 

Vandyke  brown,  246. 

Van  Ruymbeke  process  for  glycerine, 

384. 

Varec,  as  source  of  iodine,  252. 
Varnishes,  397. 
Vaseline,  343. 
Vegetable  drying  oils,  357. 

non-drying  oils,  362. 

semi-drying  oils,  359. 

oils,  obtaining  from   various   sources, 

352. 

Vellum,  582. 
Venetian  red,  243. 
Verdigris,  237. 
Vermilion,  244. 
Vermilionettes,  245. 
Vinasse,  157. 
Vinegar,  463. 

cider,  466. 

malt,  466. 

"mother  of,"  464. 

spirit,  466. 

wine,  466. 
Violet  glass,  208. 
Viscose,  490. 

silk,  497. 


INDEX 


665 


Vitrified  tiles,  218. 
Vitriol,  blue,  280. 

green,  279. 

oil  of,  62. 

white,  281. 
Vulcanite,  591. 
Vulcanization  of  rubber,  588. 
Vulcanized  fibre,  566. 

W 

Wash  leather,  583. 
Washing  machine  for  cotton,  503. 
Washoe  process  for  silver,  629. 
Water,  46. 

alkaline,  47. 

hard,  47. 

purification  of,  48. 

saline,  47. 

soft,  47. 
Water-gas,  39,  312. 

theoretical  composition  of,  40. 
Water-glass,  271. 
"Water  marks"  in  paper,  565. 
Wattle,  as  tannin  source,  521. 
Waxes,  368. 

Wedge  furnace  for  sulphide  ores,  69. 
Wedgwood  ware,  216. 
"Weissbier,"  455. 

Weldon's  apparatus  for  chlorine,  117. 
"Weldon  mud,"  118. 
Weldon-Pechiney  process  for  chlorine, 

123. 

Westphal's  balance,  28. 
Whiskey,  461. 

Irish,  462. 

Scotch,  462. 

White-Howell  roasting  furnace,  598. 
White  arsenic,  269. 

lead,  223. 

pigments,  223. 

vitriol,  281. 

zinc,  229. 
Whiting,  231. 

Whiting's  electrolytic  cell,  128. 
Wilkinson  process  for  water-gas,  314. 
Willesden  paper,  566. 
Window  glass,  205,  210. 
Wine,  440. 


artificial,  443. 

"diseases"  of,  442. 
Wise  sulphur  burner,  58. 
Woad  vat  for  indigo,  541. 
Wohlwill  electrical  method  of  "parting' 

bullion,  635. 
Wood,  as  fuel,  32. 

destructive  distillation  of,  301. 

pulp,  554. 

spirit,  305. 

tar,  309. 

vinegar,  304,  307. 
Wool,  497. 

bleaching,  510. 

dyeing,  532,  534,  535,  538,  639,  541. 

grease,  369,  499. 

scouring,  499. 

"stoving,"  511. 
Wort,  450. 
"Wove"  paper,  565. 
Wrapping  paper,  565. 
Writing  paper,  565. 
Wrought  iron,  604. 


Yaryan  evaporator,  6. 
Yeast,  436. 

compressed,  439. 

"wild,"  438. 
Yellow  glass,  207. 

ochre,  240. 

phosphorus,  257. 

pigments,  238. 

"prussiate  of  potash,"  292. 
Yorkshire  grease,  500. 
Young  fustic,  526. 


Zinc,  623. 

chromate,  239. 

dust,  624. 

oxide,  229. 

retorts  for  distillation  of,  623. 

sulphide,  230. 

white,  229. 

Zinc-lime  vat  for  indigo  dyeing,  542. 
Zones  in  the  blast  furnace,  602. 


Printed  in  the  United  States  of  America. 


o 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


AN  INITIAL  FINE  OP  25  CENTS 

WILL  BE  ASSESSED  FOR  FAILURE  TO  RETURN 
THIS  BOOK  ON  THE  DATE  DUE.  THE  PENALTY 
WILL  INCREASE  TO  SO  CENTS  ON  THE  FOURTH 
DAY  AND  TO  $1.OO  ON  THE  SEVENTH  DAY 
OVERDUE. 


FEB    14   1940 


'"    JO  . 


JUM  8  1941 


MAR   12  1948 


1966  76 


LD  21-100m-7,'39(402s) 


YC  ^920  • 


THE  UNIVERSITY  OF  CALIFORNIA  iflBRARY 


